MERGE ... WHEN NOT MATCHED BY SOURCE

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
new file mode 100644
index b87ad5c..1482ede
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -396,8 +396,8 @@
     originally matched appears later in the list of actions.
     On the other hand, if the row is concurrently updated or deleted so
     that the join condition fails, then <command>MERGE</command> will
-    evaluate the condition's <literal>NOT MATCHED</literal> actions next,
-    and execute the first one that succeeds.
+    evaluate the condition's <literal>NOT MATCHED [BY TARGET]</literal>
+    actions next, and execute the first one that succeeds.
     If <command>MERGE</command> attempts an <command>INSERT</command>
     and a unique index is present and a duplicate row is concurrently
     inserted, then a uniqueness violation error is raised;
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
new file mode 100644
index 0995fe0..8ef121a
--- a/doc/src/sgml/ref/merge.sgml
+++ b/doc/src/sgml/ref/merge.sgml
@@ -33,7 +33,8 @@ USING <replaceable class="parameter">dat
 <phrase>and <replaceable class="parameter">when_clause</replaceable> is:</phrase>
 
 { WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
-  WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
+  WHEN NOT MATCHED BY SOURCE [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
+  WHEN NOT MATCHED [BY TARGET] [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
 
 <phrase>and <replaceable class="parameter">merge_insert</replaceable> is:</phrase>
 
@@ -70,7 +71,9 @@ DELETE
    from <replaceable class="parameter">data_source</replaceable> to
    <replaceable class="parameter">target_table_name</replaceable>
    producing zero or more candidate change rows.  For each candidate change
-   row, the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal>
+   row, the status of <literal>MATCHED</literal>,
+   <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>
    is set just once, after which <literal>WHEN</literal> clauses are evaluated
    in the order specified.  For each candidate change row, the first clause to
    evaluate as true is executed.  No more than one <literal>WHEN</literal>
@@ -226,16 +229,37 @@ DELETE
       At least one <literal>WHEN</literal> clause is required.
      </para>
      <para>
+      The <literal>WHEN</literal> clause may specify <literal>WHEN MATCHED</literal>,
+      <literal>WHEN NOT MATCHED BY SOURCE</literal>, or
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>.
+      Note that the <acronym>SQL</acronym> standard only defines
+      <literal>WHEN MATCHED</literal> and <literal>WHEN NOT MATCHED</literal>
+      (which is defined to mean no matching target row).
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> is an extension to the
+      <acronym>SQL</acronym> standard, as is the option to append
+      <literal>BY TARGET</literal> to <literal>WHEN NOT MATCHED</literal>, to
+      make its meaning more explicit.
+     </para>
+     <para>
       If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
-      and the candidate change row matches a row in the
+      and the candidate change row matches a row in the source to a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
      </para>
      <para>
-      Conversely, if the <literal>WHEN</literal> clause specifies
-      <literal>WHEN NOT MATCHED</literal>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> and the candidate change
+      row represents a row in the
+      <replaceable class="parameter">target_table_name</replaceable> that does
+      not match a source row, the <literal>WHEN</literal> clause is executed
+      if the <replaceable class="parameter">condition</replaceable> is
+      absent or it evaluates to <literal>true</literal>.
+     </para>
+     <para>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>
       and the candidate change row does not match a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
@@ -257,7 +281,10 @@ DELETE
      <para>
       A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
       in both the source and the target relations. A condition on a
-      <literal>WHEN NOT MATCHED</literal> clause can only refer to columns from
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> clause can only refer to
+      columns from the target relation, since by definition there is no matching
+      source row. A condition on a <literal>WHEN NOT MATCHED [BY TARGET]</literal>
+      clause can only refer to columns from
       the source relation, since by definition there is no matching target row.
       Only the system attributes from the target table are accessible.
      </para>
@@ -382,8 +409,10 @@ DELETE
       <literal>WHEN MATCHED</literal> clause, the expression can use values
       from the original row in the target table, and values from the
       <literal>data_source</literal> row.
-      If used in a <literal>WHEN NOT MATCHED</literal> clause, the
-      expression can use values from the <literal>data_source</literal>.
+      If used in a <literal>WHEN NOT MATCHED BY SOURCE</literal> clause, the
+      expression can only use values from the original row in the target table.
+      If used in a <literal>WHEN NOT MATCHED [BY TARGET]</literal> clause, the
+      expression can only use values from the <literal>data_source</literal>.
      </para>
     </listitem>
    </varlistentry>
@@ -452,8 +481,9 @@ MERGE <replaceable class="parameter">tot
        <orderedlist>
         <listitem>
          <para>
-          Evaluate whether each row is <literal>MATCHED</literal> or
-          <literal>NOT MATCHED</literal>.
+          Evaluate whether each row is <literal>MATCHED</literal>,
+          <literal>NOT MATCHED BY SOURCE</literal>, or
+          <literal>NOT MATCHED [BY TARGET]</literal>.
          </para>
         </listitem>
         <listitem>
@@ -528,7 +558,8 @@ MERGE <replaceable class="parameter">tot
   <para>
    If a <literal>WHEN</literal> clause omits an <literal>AND</literal>
    sub-clause, it becomes the final reachable clause of that
-   kind (<literal>MATCHED</literal> or <literal>NOT MATCHED</literal>).
+   kind (<literal>MATCHED</literal>, <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>).
    If a later <literal>WHEN</literal> clause of that kind
    is specified it would be provably unreachable and an error is raised.
    If no final reachable clause is specified of either kind, it is
@@ -619,6 +650,23 @@ WHEN MATCHED THEN
    temporary table recently loaded into the database.
   </para>
 
+  <para>
+   Update <literal>wine</literal> based on a replacement wine list, inserting
+   rows for any new stock, updating modified stock entries, and deleting any
+   wines not present in the new list.
+<programlisting>
+MERGE INTO wines w
+USING new_wine_list s
+ON s.winename = w.winename
+WHEN NOT MATCHED BY TARGET THEN
+  INSERT VALUES(s.winename, s.stock)
+WHEN MATCHED AND w.stock != s.stock THEN
+  UPDATE SET stock = s.stock
+WHEN NOT MATCHED BY SOURCE THEN
+  DELETE;
+</programlisting>
+  </para>
+
  </refsect1>
 
  <refsect1>
@@ -627,7 +675,10 @@ WHEN MATCHED THEN
     This command conforms to the <acronym>SQL</acronym> standard.
   </para>
    <para>
-    The WITH clause and <literal>DO NOTHING</literal> action are extensions to
+    The WITH clause, <literal>BY SOURCE</literal> and
+    <literal>BY TARGET</literal> qualifiers to
+    <literal>WHEN NOT MATCHED</literal>, and
+    <literal>DO NOTHING</literal> action are extensions to
     the <acronym>SQL</acronym> standard.
   </para>
  </refsect1>
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
new file mode 100644
index 4cec12a..ed538e5
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -142,7 +142,6 @@ transform_MERGE_to_join(Query *parse)
 {
 	RangeTblEntry *joinrte;
 	JoinExpr   *joinexpr;
-	JoinType	jointype;
 	int			joinrti;
 	List	   *vars;
 
@@ -152,20 +151,10 @@ transform_MERGE_to_join(Query *parse)
 	/* XXX probably bogus */
 	vars = NIL;
 
-	/*
-	 * When any WHEN NOT MATCHED THEN INSERT clauses exist, we need to use an
-	 * outer join so that we process all unmatched tuples from the source
-	 * relation.  If none exist, we can use an inner join.
-	 */
-	if (parse->mergeUseOuterJoin)
-		jointype = JOIN_RIGHT;
-	else
-		jointype = JOIN_INNER;
-
 	/* Manufacture a join RTE to use. */
 	joinrte = makeNode(RangeTblEntry);
 	joinrte->rtekind = RTE_JOIN;
-	joinrte->jointype = jointype;
+	joinrte->jointype = parse->mergeJoinType;
 	joinrte->joinmergedcols = 0;
 	joinrte->joinaliasvars = vars;
 	joinrte->joinleftcols = NIL;	/* MERGE does not allow JOIN USING */
@@ -189,7 +178,7 @@ transform_MERGE_to_join(Query *parse)
 	 * Create a JOIN between the target and the source relation.
 	 */
 	joinexpr = makeNode(JoinExpr);
-	joinexpr->jointype = jointype;
+	joinexpr->jointype = parse->mergeJoinType;
 	joinexpr->isNatural = false;
 	joinexpr->larg = (Node *) makeNode(RangeTblRef);
 	((RangeTblRef *) joinexpr->larg)->rtindex = parse->resultRelation;
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
new file mode 100644
index 137b283..1a4e13e
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -157,15 +157,14 @@ preprocess_targetlist(PlannerInfo *root)
 			/*
 			 * Add resjunk entries for any Vars used in each action's
 			 * targetlist and WHEN condition that belong to relations other
-			 * than target.  Note that aggregates, window functions and
-			 * placeholder vars are not possible anywhere in MERGE's WHEN
-			 * clauses.  (PHVs may be added later, but they don't concern us
-			 * here.)
+			 * than target.  Note that aggregates and window functions are not
+			 * possible anywhere in MERGE's WHEN clauses, but PlaceHolderVars
+			 * may have been added by subquery pullup.
 			 */
 			vars = pull_var_clause((Node *)
 								   list_concat_copy((List *) action->qual,
 													action->targetList),
-								   0);
+								   PVC_INCLUDE_PLACEHOLDERS);
 			foreach(l2, vars)
 			{
 				Var		   *var = (Var *) lfirst(l2);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index 63b4baa..95531ab
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -273,6 +273,7 @@ static Node *makeRecursiveViewSelect(cha
 	struct SelectLimit *selectlimit;
 	SetQuantifier setquantifier;
 	struct GroupClause *groupclause;
+	MergeMatchKind mergematch;
 	MergeWhenClause *mergewhen;
 	struct KeyActions *keyactions;
 	struct KeyAction *keyaction;
@@ -512,6 +513,7 @@ static Node *makeRecursiveViewSelect(cha
 %type <onconflict> opt_on_conflict
 %type <mergewhen>	merge_insert merge_update merge_delete
 
+%type <mergematch> merge_when_tgt_matched merge_when_tgt_not_matched
 %type <node>	merge_when_clause opt_merge_when_condition
 %type <list>	merge_when_list
 
@@ -740,11 +742,11 @@ static Node *makeRecursiveViewSelect(cha
 
 	SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
-	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
+	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SOURCE SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRIP_P
 	SUBSCRIPTION SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
 
-	TABLE TABLES TABLESAMPLE TABLESPACE TEMP TEMPLATE TEMPORARY TEXT_P THEN
+	TABLE TABLES TABLESAMPLE TABLESPACE TARGET TEMP TEMPLATE TEMPORARY TEXT_P THEN
 	TIES TIME TIMESTAMP TO TRAILING TRANSACTION TRANSFORM
 	TREAT TRIGGER TRIM TRUE_P
 	TRUNCATE TRUSTED TYPE_P TYPES_P
@@ -12260,49 +12262,59 @@ merge_when_list:
 		;
 
 merge_when_clause:
-			WHEN MATCHED opt_merge_when_condition THEN merge_update
+			merge_when_tgt_matched opt_merge_when_condition THEN merge_update
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN merge_delete
+			| merge_when_tgt_matched opt_merge_when_condition THEN merge_delete
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN merge_insert
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN merge_insert
 				{
-					$6->matched = false;
-					$6->condition = $4;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $6;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = true;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $3;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = false;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $4;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
 		;
 
+merge_when_tgt_matched:
+			WHEN MATCHED					{ $$ = MERGE_WHEN_MATCHED; }
+			| WHEN NOT MATCHED BY SOURCE	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_SOURCE; }
+		;
+
+merge_when_tgt_not_matched:
+			WHEN NOT MATCHED				{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+			| WHEN NOT MATCHED BY TARGET	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+		;
+
 opt_merge_when_condition:
 			AND a_expr				{ $$ = $2; }
 			|						{ $$ = NULL; }
@@ -16961,6 +16973,7 @@ unreserved_keyword:
 			| SIMPLE
 			| SKIP
 			| SNAPSHOT
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -16979,6 +16992,7 @@ unreserved_keyword:
 			| SYSTEM_P
 			| TABLES
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
@@ -17555,6 +17569,7 @@ bare_label_keyword:
 			| SMALLINT
 			| SNAPSHOT
 			| SOME
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -17578,6 +17593,7 @@ bare_label_keyword:
 			| TABLES
 			| TABLESAMPLE
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
diff --git a/src/backend/parser/parse_merge.c b/src/backend/parser/parse_merge.c
new file mode 100644
index 3844f2b..997b7e2
--- a/src/backend/parser/parse_merge.c
+++ b/src/backend/parser/parse_merge.c
@@ -43,9 +43,9 @@ static void setNamespaceVisibilityForRTE
  * Make appropriate changes to the namespace visibility while transforming
  * individual action's quals and targetlist expressions. In particular, for
  * INSERT actions we must only see the source relation (since INSERT action is
- * invoked for NOT MATCHED tuples and hence there is no target tuple to deal
- * with). On the other hand, UPDATE and DELETE actions can see both source and
- * target relations.
+ * invoked for NOT MATCHED [BY TARGET] tuples and hence there is no target
+ * tuple to deal with). On the other hand, UPDATE and DELETE actions can see
+ * both source and target relations, unless invoked for NOT MATCH BY SOURCE.
  *
  * Also, since the internal join node can hide the source and target
  * relations, we must explicitly make the respective relation as visible so
@@ -61,7 +61,7 @@ setNamespaceForMergeWhen(ParseState *pst
 	targetRelRTE = rt_fetch(targetRTI, pstate->p_rtable);
 	sourceRelRTE = rt_fetch(sourceRTI, pstate->p_rtable);
 
-	if (mergeWhenClause->matched)
+	if (mergeWhenClause->matchKind == MERGE_WHEN_MATCHED)
 	{
 		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
 			   mergeWhenClause->commandType == CMD_DELETE ||
@@ -73,11 +73,25 @@ setNamespaceForMergeWhen(ParseState *pst
 		setNamespaceVisibilityForRTE(pstate->p_namespace,
 									 sourceRelRTE, true, true);
 	}
-	else
+	else if (mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
 	{
 		/*
-		 * NOT MATCHED actions can't see target relation, but they can see
-		 * source relation.
+		 * NOT MATCHED BY SOURCE actions can see the target relation, but they
+		 * can't see the source relation.
+		 */
+		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
+			   mergeWhenClause->commandType == CMD_DELETE ||
+			   mergeWhenClause->commandType == CMD_NOTHING);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 targetRelRTE, true, true);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 sourceRelRTE, false, false);
+	}
+	else	/* mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_TARGET */
+	{
+		/*
+		 * NOT MATCHED [BY TARGET] actions can't see target relation, but they
+		 * can see source relation.
 		 */
 		Assert(mergeWhenClause->commandType == CMD_INSERT ||
 			   mergeWhenClause->commandType == CMD_NOTHING);
@@ -98,7 +112,9 @@ transformMergeStmt(ParseState *pstate, M
 	Query	   *qry = makeNode(Query);
 	ListCell   *l;
 	AclMode		targetPerms = ACL_NO_RIGHTS;
-	bool		is_terminal[2];
+	bool		is_terminal[3];
+	bool		left_join;
+	bool		right_join;
 	Index		sourceRTI;
 	List	   *mergeActionList;
 	Node	   *joinExpr;
@@ -127,10 +143,12 @@ transformMergeStmt(ParseState *pstate, M
 	 */
 	is_terminal[0] = false;
 	is_terminal[1] = false;
+	is_terminal[2] = false;
+	left_join = false;
+	right_join = false;
 	foreach(l, stmt->mergeWhenClauses)
 	{
 		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
-		int			when_type = (mergeWhenClause->matched ? 0 : 1);
 
 		/*
 		 * Collect action types so we can check target permissions
@@ -155,14 +173,33 @@ transformMergeStmt(ParseState *pstate, M
 		/*
 		 * Check for unreachable WHEN clauses
 		 */
-		if (mergeWhenClause->condition == NULL)
-			is_terminal[when_type] = true;
-		else if (is_terminal[when_type])
+		if (is_terminal[mergeWhenClause->matchKind])
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
 					 errmsg("unreachable WHEN clause specified after unconditional WHEN clause")));
+		if (mergeWhenClause->condition == NULL)
+			is_terminal[mergeWhenClause->matchKind] = true;
+
+		/* Is left/right/full outer join required? */
+		if (mergeWhenClause->commandType != CMD_NOTHING)
+		{
+			if (mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+				left_join = true;
+			if (mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_TARGET)
+				right_join = true;
+		}
 	}
 
+	/* Join type required */
+	if (left_join && right_join)
+		qry->mergeJoinType = JOIN_FULL;
+	else if (left_join)
+		qry->mergeJoinType = JOIN_LEFT;
+	else if (right_join)
+		qry->mergeJoinType = JOIN_RIGHT;
+	else
+		qry->mergeJoinType = JOIN_INNER;
+
 	/*
 	 * Set up the MERGE target table.  The target table is added to the
 	 * namespace below and to joinlist in transform_MERGE_to_join, so don't
@@ -251,15 +288,19 @@ transformMergeStmt(ParseState *pstate, M
 	foreach(l, stmt->mergeWhenClauses)
 	{
 		MergeWhenClause *mergeWhenClause = lfirst_node(MergeWhenClause, l);
+		MergeMatchKind matchKind = mergeWhenClause->matchKind;
 		MergeAction *action;
 
 		action = makeNode(MergeAction);
 		action->commandType = mergeWhenClause->commandType;
-		action->matched = mergeWhenClause->matched;
 
-		/* Use an outer join if any INSERT actions exist in the command. */
-		if (action->commandType == CMD_INSERT)
-			qry->mergeUseOuterJoin = true;
+		/*
+		 * For planning and execution purposes, MATCHED and NOT MATCHED BY
+		 * SOURCE actions are handled the same, since they each must match
+		 * target rows.  Thus we need only note whether the action is NOT
+		 * MATCHED [BY TARGET].
+		 */
+		action->matched = matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET;
 
 		/*
 		 * Set namespace for the specific action. This must be done before
@@ -280,6 +321,50 @@ transformMergeStmt(ParseState *pstate, M
 											EXPR_KIND_MERGE_WHEN, "WHEN");
 
 		/*
+		 * If we are doing a left or full join that includes target-only rows
+		 * (NOT MATCHED BY SOURCE), add additional WHEN conditions to each
+		 * action to test if the source row matches.
+		 *
+		 * This distinguishes NOT MATCHED BY SOURCE actions (identified by a
+		 * "source IS NOT DISTINCT FROM NULL" clause) from MATCHED actions
+		 * (identified by a "source IS DISTINCT FROM NULL" clause).
+		 *
+		 * Additionally, a "source IS DISTINCT FROM NULL" clause is required
+		 * for NOT MATCHED [BY TARGET] actions in case the executor attempts
+		 * to invoke such an action for a concurrently deleted target row that
+		 * ends up matching neither source nor target.
+		 */
+		if (left_join)
+		{
+			bool		src_null;
+			NullTest   *ntest;
+
+			/* Make a "source IS [NOT] DISTINCT FROM NULL" clause */
+			src_null = matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE;
+
+			ntest = makeNode(NullTest);
+
+			ntest->arg = (Expr *) makeVar(sourceRTI,
+										  InvalidAttrNumber,
+										  RECORDOID,
+										  -1,
+										  InvalidOid,
+										  0);
+			ntest->nulltesttype = src_null ? IS_NULL : IS_NOT_NULL;
+			ntest->argisrow = false;
+			ntest->location = -1;
+
+			/* Combine it with the action's WHEN condition */
+			if (action->qual == NULL)
+				action->qual = (Node *) ntest;
+			else
+				action->qual =
+					(Node *) makeBoolExpr(AND_EXPR,
+										  list_make2(ntest, action->qual),
+										  -1);
+		}
+
+		/*
 		 * Transform target lists for each INSERT and UPDATE action stmt
 		 */
 		switch (action->commandType)
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
new file mode 100644
index 34bc640..e9636c8
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -159,7 +159,7 @@ typedef struct Query
 								 * also USING clause for MERGE */
 
 	List	   *mergeActionList;	/* list of actions for MERGE (only) */
-	bool		mergeUseOuterJoin;	/* whether to use outer join */
+	JoinType	mergeJoinType;		/* MERGE target to source join type */
 
 	List	   *targetList;		/* target list (of TargetEntry) */
 
@@ -1586,6 +1586,14 @@ typedef struct CommonTableExpr
 	 ((Query *) (cte)->ctequery)->targetList : \
 	 ((Query *) (cte)->ctequery)->returningList)
 
+/* MATCHED/NOT MATCHED specification for MergeWhenClause */
+typedef enum MergeMatchKind
+{
+	MERGE_WHEN_MATCHED,
+	MERGE_WHEN_NOT_MATCHED_BY_SOURCE,
+	MERGE_WHEN_NOT_MATCHED_BY_TARGET
+} MergeMatchKind;
+
 /*
  * MergeWhenClause -
  *		raw parser representation of a WHEN clause in a MERGE statement
@@ -1595,7 +1603,7 @@ typedef struct CommonTableExpr
 typedef struct MergeWhenClause
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *condition;		/* WHEN conditions (raw parser) */
@@ -1611,7 +1619,8 @@ typedef struct MergeWhenClause
 typedef struct MergeAction
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	bool		matched;		/* true if target matches (input matchKind is
+								 * MATCHED or NOT MATCHED BY SOURCE) */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *qual;			/* transformed WHEN conditions */
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
new file mode 100644
index 957ee18..fd94b0b
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -391,6 +391,7 @@ PG_KEYWORD("skip", SKIP, UNRESERVED_KEYW
 PG_KEYWORD("smallint", SMALLINT, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("snapshot", SNAPSHOT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("some", SOME, RESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("source", SOURCE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("sql", SQL_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("stable", STABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("standalone", STANDALONE_P, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -414,6 +415,7 @@ PG_KEYWORD("table", TABLE, RESERVED_KEYW
 PG_KEYWORD("tables", TABLES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablesample", TABLESAMPLE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablespace", TABLESPACE, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("target", TARGET, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temp", TEMP, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("template", TEMPLATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temporary", TEMPORARY, UNRESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/test/regress/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index 6c8a18f..e99623a
--- a/src/test/regress/expected/merge.out
+++ b/src/test/regress/expected/merge.out
@@ -71,6 +71,15 @@ WHEN MATCHED THEN
 ERROR:  syntax error at or near "INSERT"
 LINE 5:  INSERT DEFAULT VALUES;
          ^
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
+ERROR:  syntax error at or near "INSERT"
+LINE 5:  INSERT DEFAULT VALUES;
+         ^
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -107,6 +116,15 @@ WHEN NOT MATCHED THEN
 ERROR:  syntax error at or near "UPDATE"
 LINE 5:  UPDATE SET balance = 0;
          ^
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
+ERROR:  syntax error at or near "UPDATE"
+LINE 5:  UPDATE SET balance = 0;
+         ^
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -271,6 +289,22 @@ SELECT * FROM target ORDER BY tid;
 (4 rows)
 
 ROLLBACK;
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   4 |      40
+(1 row)
+
+ROLLBACK;
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -738,6 +772,19 @@ SELECT * FROM wq_target;
    1 |      -1
 (1 row)
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+ERROR:  invalid reference to FROM-clause entry for table "s"
+LINE 3: WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+                                       ^
+DETAIL:  There is an entry for table "s", but it cannot be referenced from this part of the query.
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
  balance | sid 
@@ -923,6 +970,45 @@ SELECT * FROM target ORDER BY tid;
 (3 rows)
 
 ROLLBACK;
+-- UPSERT with UPDATE/DELETE not matched
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE DELETE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  BEFORE INSERT ROW trigger row: (4,40)
+NOTICE:  BEFORE DELETE ROW trigger row: (2,20)
+NOTICE:  BEFORE UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  AFTER INSERT ROW trigger row: (4,40)
+NOTICE:  AFTER DELETE ROW trigger row: (2,20)
+NOTICE:  AFTER UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER DELETE STATEMENT trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |       0
+   3 |      10
+   4 |      40
+(3 rows)
+
+ROLLBACK;
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -1436,6 +1522,50 @@ WHEN NOT MATCHED AND s.a < 20 THEN
                ->  Seq Scan on ex_mtarget t (actual rows=49 loops=1)
 (12 rows)
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=54
+   ->  Merge Left Join (actual rows=54 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=100
+   ->  Merge Full Join (actual rows=100 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index 98fe104..c641214
--- a/src/test/regress/sql/merge.sql
+++ b/src/test/regress/sql/merge.sql
@@ -51,6 +51,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN MATCHED THEN
 	INSERT DEFAULT VALUES;
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -75,6 +81,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN NOT MATCHED THEN
 	UPDATE SET balance = 0;
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -213,6 +225,18 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -497,6 +521,17 @@ WHEN NOT MATCHED AND s.balance = 100 THE
 	INSERT (tid) VALUES (s.sid);
 SELECT * FROM wq_target;
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
+
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
 MERGE INTO wq_target t
@@ -624,6 +659,25 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- UPSERT with UPDATE/DELETE not matched
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -916,6 +970,20 @@ WHEN MATCHED AND t.a >= 30 AND t.a <= 40
 WHEN NOT MATCHED AND s.a < 20 THEN
 	INSERT VALUES (a, b)');
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
new file mode 100644
index b87ad5c..1482ede
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -396,8 +396,8 @@
     originally matched appears later in the list of actions.
     On the other hand, if the row is concurrently updated or deleted so
     that the join condition fails, then <command>MERGE</command> will
-    evaluate the condition's <literal>NOT MATCHED</literal> actions next,
-    and execute the first one that succeeds.
+    evaluate the condition's <literal>NOT MATCHED [BY TARGET]</literal>
+    actions next, and execute the first one that succeeds.
     If <command>MERGE</command> attempts an <command>INSERT</command>
     and a unique index is present and a duplicate row is concurrently
     inserted, then a uniqueness violation error is raised;
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
new file mode 100644
index 0995fe0..8ef121a
--- a/doc/src/sgml/ref/merge.sgml
+++ b/doc/src/sgml/ref/merge.sgml
@@ -33,7 +33,8 @@ USING <replaceable class="parameter">dat
 <phrase>and <replaceable class="parameter">when_clause</replaceable> is:</phrase>
 
 { WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
-  WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
+  WHEN NOT MATCHED BY SOURCE [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
+  WHEN NOT MATCHED [BY TARGET] [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
 
 <phrase>and <replaceable class="parameter">merge_insert</replaceable> is:</phrase>
 
@@ -70,7 +71,9 @@ DELETE
    from <replaceable class="parameter">data_source</replaceable> to
    <replaceable class="parameter">target_table_name</replaceable>
    producing zero or more candidate change rows.  For each candidate change
-   row, the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal>
+   row, the status of <literal>MATCHED</literal>,
+   <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>
    is set just once, after which <literal>WHEN</literal> clauses are evaluated
    in the order specified.  For each candidate change row, the first clause to
    evaluate as true is executed.  No more than one <literal>WHEN</literal>
@@ -226,16 +229,37 @@ DELETE
       At least one <literal>WHEN</literal> clause is required.
      </para>
      <para>
+      The <literal>WHEN</literal> clause may specify <literal>WHEN MATCHED</literal>,
+      <literal>WHEN NOT MATCHED BY SOURCE</literal>, or
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>.
+      Note that the <acronym>SQL</acronym> standard only defines
+      <literal>WHEN MATCHED</literal> and <literal>WHEN NOT MATCHED</literal>
+      (which is defined to mean no matching target row).
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> is an extension to the
+      <acronym>SQL</acronym> standard, as is the option to append
+      <literal>BY TARGET</literal> to <literal>WHEN NOT MATCHED</literal>, to
+      make its meaning more explicit.
+     </para>
+     <para>
       If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
-      and the candidate change row matches a row in the
+      and the candidate change row matches a row in the source to a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
      </para>
      <para>
-      Conversely, if the <literal>WHEN</literal> clause specifies
-      <literal>WHEN NOT MATCHED</literal>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> and the candidate change
+      row represents a row in the
+      <replaceable class="parameter">target_table_name</replaceable> that does
+      not match a source row, the <literal>WHEN</literal> clause is executed
+      if the <replaceable class="parameter">condition</replaceable> is
+      absent or it evaluates to <literal>true</literal>.
+     </para>
+     <para>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>
       and the candidate change row does not match a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
@@ -257,7 +281,10 @@ DELETE
      <para>
       A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
       in both the source and the target relations. A condition on a
-      <literal>WHEN NOT MATCHED</literal> clause can only refer to columns from
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> clause can only refer to
+      columns from the target relation, since by definition there is no matching
+      source row. A condition on a <literal>WHEN NOT MATCHED [BY TARGET]</literal>
+      clause can only refer to columns from
       the source relation, since by definition there is no matching target row.
       Only the system attributes from the target table are accessible.
      </para>
@@ -382,8 +409,10 @@ DELETE
       <literal>WHEN MATCHED</literal> clause, the expression can use values
       from the original row in the target table, and values from the
       <literal>data_source</literal> row.
-      If used in a <literal>WHEN NOT MATCHED</literal> clause, the
-      expression can use values from the <literal>data_source</literal>.
+      If used in a <literal>WHEN NOT MATCHED BY SOURCE</literal> clause, the
+      expression can only use values from the original row in the target table.
+      If used in a <literal>WHEN NOT MATCHED [BY TARGET]</literal> clause, the
+      expression can only use values from the <literal>data_source</literal>.
      </para>
     </listitem>
    </varlistentry>
@@ -452,8 +481,9 @@ MERGE <replaceable class="parameter">tot
        <orderedlist>
         <listitem>
          <para>
-          Evaluate whether each row is <literal>MATCHED</literal> or
-          <literal>NOT MATCHED</literal>.
+          Evaluate whether each row is <literal>MATCHED</literal>,
+          <literal>NOT MATCHED BY SOURCE</literal>, or
+          <literal>NOT MATCHED [BY TARGET]</literal>.
          </para>
         </listitem>
         <listitem>
@@ -528,7 +558,8 @@ MERGE <replaceable class="parameter">tot
   <para>
    If a <literal>WHEN</literal> clause omits an <literal>AND</literal>
    sub-clause, it becomes the final reachable clause of that
-   kind (<literal>MATCHED</literal> or <literal>NOT MATCHED</literal>).
+   kind (<literal>MATCHED</literal>, <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>).
    If a later <literal>WHEN</literal> clause of that kind
    is specified it would be provably unreachable and an error is raised.
    If no final reachable clause is specified of either kind, it is
@@ -619,6 +650,23 @@ WHEN MATCHED THEN
    temporary table recently loaded into the database.
   </para>
 
+  <para>
+   Update <literal>wine</literal> based on a replacement wine list, inserting
+   rows for any new stock, updating modified stock entries, and deleting any
+   wines not present in the new list.
+<programlisting>
+MERGE INTO wines w
+USING new_wine_list s
+ON s.winename = w.winename
+WHEN NOT MATCHED BY TARGET THEN
+  INSERT VALUES(s.winename, s.stock)
+WHEN MATCHED AND w.stock != s.stock THEN
+  UPDATE SET stock = s.stock
+WHEN NOT MATCHED BY SOURCE THEN
+  DELETE;
+</programlisting>
+  </para>
+
  </refsect1>
 
  <refsect1>
@@ -627,7 +675,10 @@ WHEN MATCHED THEN
     This command conforms to the <acronym>SQL</acronym> standard.
   </para>
    <para>
-    The WITH clause and <literal>DO NOTHING</literal> action are extensions to
+    The WITH clause, <literal>BY SOURCE</literal> and
+    <literal>BY TARGET</literal> qualifiers to
+    <literal>WHEN NOT MATCHED</literal>, and
+    <literal>DO NOTHING</literal> action are extensions to
     the <acronym>SQL</acronym> standard.
   </para>
  </refsect1>
diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
new file mode 100644
index 651ad24..005da8d
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -898,8 +898,16 @@ ExecInitPartitionInfo(ModifyTableState *
 			action_state = makeNode(MergeActionState);
 			action_state->mas_action = action;
 
-			/* And put the action in the appropriate list */
-			if (action->matched)
+			/*
+			 * Put the action in the appropriate list.
+			 *
+			 * Note that the executor treats WHEN NOT MATCHED BY SOURCE
+			 * actions in exactly the same way as WHEN MATCHED actions, since
+			 * they both match the target (see ExecMerge).  Thus both types go
+			 * in the "matched" list.  Only WHEN NOT MATCHED BY TARGET actions
+			 * go in the "not matched" list.
+			 */
+			if (action->matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET)
 				list = &leaf_part_rri->ri_matchedMergeAction;
 			else
 				list = &leaf_part_rri->ri_notMatchedMergeAction;
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
new file mode 100644
index 687a542..339ba68
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -24,13 +24,15 @@
  *		values plus row-locating info for UPDATE and MERGE cases, or just the
  *		row-locating info for DELETE cases.
  *
- *		MERGE runs a join between the source relation and the target
- *		table; if any WHEN NOT MATCHED clauses are present, then the
- *		join is an outer join.  In this case, any unmatched tuples will
- *		have NULL row-locating info, and only INSERT can be run. But for
- *		matched tuples, then row-locating info is used to determine the
- *		tuple to UPDATE or DELETE. When all clauses are WHEN MATCHED,
- *		then an inner join is used, so all tuples contain row-locating info.
+ *		MERGE runs a join between the source relation and the target table.
+ *		If any WHEN NOT MATCHED [BY TARGET] clauses are present, then the join
+ *		is an outer join that might output tuples without a matching target
+ *		tuple.  In this case, any unmatched target tuples will have NULL
+ *		row-locating info, and only INSERT can be run.  But for matched
+ *		target tuples, the row-locating info is used to determine the tuple
+ *		to UPDATE or DELETE.  When all clauses are WHEN MATCHED or WHEN NOT
+ *		MATCHED BY SOURCE, all tuples produced by the join will include a
+ *		matching target tuple, so all tuples contain row-locating info.
  *
  *		If the query specifies RETURNING, then the ModifyTable returns a
  *		RETURNING tuple after completing each row insert, update, or delete.
@@ -2695,6 +2697,20 @@ ExecMerge(ModifyTableContext *context, R
 	bool		matched;
 
 	/*-----
+	 * Note that as far as the executor is concerned, WHEN NOT MATCHED BY
+	 * SOURCE actions are treated exactly the same as WHEN MATCHED actions,
+	 * since both match target tuples.  They are distinguished from one
+	 * another by a qual that tests if the source tuple is NULL, but the
+	 * executor knows nothing about the contents of the merge action quals.
+	 * Thus WHEN MATCHED and WHEN NOT MATCHED BY SOURCE actions are stored
+	 * together in the same "matched" list.  In the case of concurrent updates
+	 * and rechecks discussed below, the target tuple might be modified, but
+	 * not the source tuple, and so there is no danger of a WHEN MATCHED case
+	 * becoming a WHEN NOT MATCHED BY SOURCE case, or vice versa.  Thus, in
+	 * the dicussion that follows "MATCHED" means "matched by target", and
+	 * should be taken to include both WHEN MATCHED and WHEN NOT MATCHED BY
+	 * SOURCE, while "NOT MATCHED" means NOT MATCHED BY TARGET.
+	 *
 	 * If we are dealing with a WHEN MATCHED case (tupleid is valid), we
 	 * execute the first action for which the additional WHEN MATCHED AND
 	 * quals pass.  If an action without quals is found, that action is
@@ -3257,8 +3273,14 @@ ExecInitMerge(ModifyTableState *mtstate,
 			 * We create two lists - one for WHEN MATCHED actions and one for
 			 * WHEN NOT MATCHED actions - and stick the MergeActionState into
 			 * the appropriate list.
+			 *
+			 * Note that the executor treats WHEN NOT MATCHED BY SOURCE
+			 * actions in exactly the same way as WHEN MATCHED actions, since
+			 * they both match the target (see ExecMerge).  Thus both types go
+			 * in the "matched" list.  Only WHEN NOT MATCHED BY TARGET actions
+			 * go in the "not matched" list.
 			 */
-			if (action_state->mas_action->matched)
+			if (action->matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET)
 				list = &resultRelInfo->ri_matchedMergeAction;
 			else
 				list = &resultRelInfo->ri_notMatchedMergeAction;
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
new file mode 100644
index cfb314e..264fa3f
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -142,6 +142,9 @@ transform_MERGE_to_join(Query *parse)
 {
 	RangeTblEntry *joinrte;
 	JoinExpr   *joinexpr;
+	ListCell   *lc;
+	bool		src_only_tuples;
+	bool		tgt_only_tuples;
 	JoinType	jointype;
 	int			joinrti;
 	List	   *vars;
@@ -153,12 +156,32 @@ transform_MERGE_to_join(Query *parse)
 	vars = NIL;
 
 	/*
-	 * When any WHEN NOT MATCHED THEN INSERT clauses exist, we need to use an
-	 * outer join so that we process all unmatched tuples from the source
-	 * relation.  If none exist, we can use an inner join.
+	 * Work out what kind of join is required.  If there any WHEN NOT MATCHED
+	 * BY SOURCE/TARGET clauses, an outer join is required so that we process
+	 * all unmatched tuples from the source and/or target relations.
+	 * Otherwise, we can use an inner join.
 	 */
-	if (parse->mergeUseOuterJoin)
+	src_only_tuples = false;
+	tgt_only_tuples = false;
+	foreach(lc, parse->mergeActionList)
+	{
+		MergeAction *action = lfirst_node(MergeAction, lc);
+
+		if (action->commandType != CMD_NOTHING)
+		{
+			if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+				tgt_only_tuples = true;
+			if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_TARGET)
+				src_only_tuples = true;
+		}
+	}
+
+	if (src_only_tuples && tgt_only_tuples)
+		jointype = JOIN_FULL;
+	else if (src_only_tuples)
 		jointype = JOIN_RIGHT;
+	else if (tgt_only_tuples)
+		jointype = JOIN_LEFT;
 	else
 		jointype = JOIN_INNER;
 
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
new file mode 100644
index c6d747b..027d2be
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -157,15 +157,14 @@ preprocess_targetlist(PlannerInfo *root)
 			/*
 			 * Add resjunk entries for any Vars used in each action's
 			 * targetlist and WHEN condition that belong to relations other
-			 * than target.  Note that aggregates, window functions and
-			 * placeholder vars are not possible anywhere in MERGE's WHEN
-			 * clauses.  (PHVs may be added later, but they don't concern us
-			 * here.)
+			 * than target.  Note that aggregates and window functions are not
+			 * possible anywhere in MERGE's WHEN clauses, but PlaceHolderVars
+			 * may have been added by subquery pullup.
 			 */
 			vars = pull_var_clause((Node *)
 								   list_concat_copy((List *) action->qual,
 													action->targetList),
-								   0);
+								   PVC_INCLUDE_PLACEHOLDERS);
 			foreach(l2, vars)
 			{
 				Var		   *var = (Var *) lfirst(l2);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index a013838..dbe0089
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -273,6 +273,7 @@ static Node *makeRecursiveViewSelect(cha
 	struct SelectLimit *selectlimit;
 	SetQuantifier setquantifier;
 	struct GroupClause *groupclause;
+	MergeMatchKind mergematch;
 	MergeWhenClause *mergewhen;
 	struct KeyActions *keyactions;
 	struct KeyAction *keyaction;
@@ -512,6 +513,7 @@ static Node *makeRecursiveViewSelect(cha
 %type <onconflict> opt_on_conflict
 %type <mergewhen>	merge_insert merge_update merge_delete
 
+%type <mergematch> merge_when_tgt_matched merge_when_tgt_not_matched
 %type <node>	merge_when_clause opt_merge_when_condition
 %type <list>	merge_when_list
 
@@ -740,11 +742,11 @@ static Node *makeRecursiveViewSelect(cha
 
 	SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
-	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
+	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SOURCE SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRIP_P
 	SUBSCRIPTION SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
 
-	TABLE TABLES TABLESAMPLE TABLESPACE TEMP TEMPLATE TEMPORARY TEXT_P THEN
+	TABLE TABLES TABLESAMPLE TABLESPACE TARGET TEMP TEMPLATE TEMPORARY TEXT_P THEN
 	TIES TIME TIMESTAMP TO TRAILING TRANSACTION TRANSFORM
 	TREAT TRIGGER TRIM TRUE_P
 	TRUNCATE TRUSTED TYPE_P TYPES_P
@@ -12260,49 +12262,59 @@ merge_when_list:
 		;
 
 merge_when_clause:
-			WHEN MATCHED opt_merge_when_condition THEN merge_update
+			merge_when_tgt_matched opt_merge_when_condition THEN merge_update
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN merge_delete
+			| merge_when_tgt_matched opt_merge_when_condition THEN merge_delete
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN merge_insert
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN merge_insert
 				{
-					$6->matched = false;
-					$6->condition = $4;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $6;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = true;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $3;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = false;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $4;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
 		;
 
+merge_when_tgt_matched:
+			WHEN MATCHED					{ $$ = MERGE_WHEN_MATCHED; }
+			| WHEN NOT MATCHED BY SOURCE	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_SOURCE; }
+		;
+
+merge_when_tgt_not_matched:
+			WHEN NOT MATCHED				{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+			| WHEN NOT MATCHED BY TARGET	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+		;
+
 opt_merge_when_condition:
 			AND a_expr				{ $$ = $2; }
 			|						{ $$ = NULL; }
@@ -16961,6 +16973,7 @@ unreserved_keyword:
 			| SIMPLE
 			| SKIP
 			| SNAPSHOT
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -16979,6 +16992,7 @@ unreserved_keyword:
 			| SYSTEM_P
 			| TABLES
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
@@ -17555,6 +17569,7 @@ bare_label_keyword:
 			| SMALLINT
 			| SNAPSHOT
 			| SOME
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -17578,6 +17593,7 @@ bare_label_keyword:
 			| TABLES
 			| TABLESAMPLE
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
diff --git a/src/backend/parser/parse_merge.c b/src/backend/parser/parse_merge.c
new file mode 100644
index 611dfce..fca2bd9
--- a/src/backend/parser/parse_merge.c
+++ b/src/backend/parser/parse_merge.c
@@ -43,9 +43,9 @@ static void setNamespaceVisibilityForRTE
  * Make appropriate changes to the namespace visibility while transforming
  * individual action's quals and targetlist expressions. In particular, for
  * INSERT actions we must only see the source relation (since INSERT action is
- * invoked for NOT MATCHED tuples and hence there is no target tuple to deal
- * with). On the other hand, UPDATE and DELETE actions can see both source and
- * target relations.
+ * invoked for NOT MATCHED [BY TARGET] tuples and hence there is no target
+ * tuple to deal with). On the other hand, UPDATE and DELETE actions can see
+ * both source and target relations, unless invoked for NOT MATCH BY SOURCE.
  *
  * Also, since the internal join node can hide the source and target
  * relations, we must explicitly make the respective relation as visible so
@@ -61,7 +61,7 @@ setNamespaceForMergeWhen(ParseState *pst
 	targetRelRTE = rt_fetch(targetRTI, pstate->p_rtable);
 	sourceRelRTE = rt_fetch(sourceRTI, pstate->p_rtable);
 
-	if (mergeWhenClause->matched)
+	if (mergeWhenClause->matchKind == MERGE_WHEN_MATCHED)
 	{
 		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
 			   mergeWhenClause->commandType == CMD_DELETE ||
@@ -73,11 +73,25 @@ setNamespaceForMergeWhen(ParseState *pst
 		setNamespaceVisibilityForRTE(pstate->p_namespace,
 									 sourceRelRTE, true, true);
 	}
-	else
+	else if (mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
 	{
 		/*
-		 * NOT MATCHED actions can't see target relation, but they can see
-		 * source relation.
+		 * NOT MATCHED BY SOURCE actions can see the target relation, but they
+		 * can't see the source relation.
+		 */
+		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
+			   mergeWhenClause->commandType == CMD_DELETE ||
+			   mergeWhenClause->commandType == CMD_NOTHING);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 targetRelRTE, true, true);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 sourceRelRTE, false, false);
+	}
+	else	/* mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_TARGET */
+	{
+		/*
+		 * NOT MATCHED [BY TARGET] actions can't see target relation, but they
+		 * can see source relation.
 		 */
 		Assert(mergeWhenClause->commandType == CMD_INSERT ||
 			   mergeWhenClause->commandType == CMD_NOTHING);
@@ -98,7 +112,8 @@ transformMergeStmt(ParseState *pstate, M
 	Query	   *qry = makeNode(Query);
 	ListCell   *l;
 	AclMode		targetPerms = ACL_NO_RIGHTS;
-	bool		is_terminal[2];
+	bool		is_terminal[3];
+	bool		tgt_only_tuples;
 	Index		sourceRTI;
 	List	   *mergeActionList;
 	Node	   *joinExpr;
@@ -125,12 +140,13 @@ transformMergeStmt(ParseState *pstate, M
 	/*
 	 * Check WHEN clauses for permissions and sanity
 	 */
-	is_terminal[0] = false;
-	is_terminal[1] = false;
+	is_terminal[MERGE_WHEN_MATCHED] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
+	tgt_only_tuples = false;
 	foreach(l, stmt->mergeWhenClauses)
 	{
 		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
-		int			when_type = (mergeWhenClause->matched ? 0 : 1);
 
 		/*
 		 * Collect action types so we can check target permissions
@@ -155,12 +171,22 @@ transformMergeStmt(ParseState *pstate, M
 		/*
 		 * Check for unreachable WHEN clauses
 		 */
-		if (mergeWhenClause->condition == NULL)
-			is_terminal[when_type] = true;
-		else if (is_terminal[when_type])
+		if (is_terminal[mergeWhenClause->matchKind])
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
 					 errmsg("unreachable WHEN clause specified after unconditional WHEN clause")));
+		if (mergeWhenClause->condition == NULL)
+			is_terminal[mergeWhenClause->matchKind] = true;
+
+		/*
+		 * Test if we have a WHEN NOT MATCHED BY SOURCE action that processes
+		 * unmatched tuples from the target relation.  If so, additional WHEN
+		 * conditions are added below to differentiate the various match
+		 * kinds.
+		 */
+		if (mergeWhenClause->commandType != CMD_NOTHING &&
+			mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+			tgt_only_tuples = true;
 	}
 
 	/*
@@ -255,11 +281,7 @@ transformMergeStmt(ParseState *pstate, M
 
 		action = makeNode(MergeAction);
 		action->commandType = mergeWhenClause->commandType;
-		action->matched = mergeWhenClause->matched;
-
-		/* Use an outer join if any INSERT actions exist in the command. */
-		if (action->commandType == CMD_INSERT)
-			qry->mergeUseOuterJoin = true;
+		action->matchKind = mergeWhenClause->matchKind;
 
 		/*
 		 * Set namespace for the specific action. This must be done before
@@ -280,6 +302,51 @@ transformMergeStmt(ParseState *pstate, M
 											EXPR_KIND_MERGE_WHEN, "WHEN");
 
 		/*
+		 * If there any WHEN NOT MATCHED BY SOURCE actions that require
+		 * unmatched tuples from the target relation to be processed, add
+		 * additional WHEN conditions to every action to check that tuples
+		 * from the source match or do not match, as necessary.
+		 *
+		 * This distinguishes NOT MATCHED BY SOURCE actions (identified by a
+		 * "source IS NOT DISTINCT FROM NULL" clause) from MATCHED actions
+		 * (identified by a "source IS DISTINCT FROM NULL" clause).
+		 *
+		 * Additionally, a "source IS DISTINCT FROM NULL" clause is required
+		 * for NOT MATCHED [BY TARGET] actions in case the executor attempts
+		 * to invoke such an action for a concurrently deleted target row that
+		 * ends up matching neither source nor target.
+		 */
+		if (tgt_only_tuples)
+		{
+			bool		src_null;
+			NullTest   *ntest;
+
+			/* Make a "source IS [NOT] DISTINCT FROM NULL" clause */
+			src_null = action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE;
+
+			ntest = makeNode(NullTest);
+
+			ntest->arg = (Expr *) makeVar(sourceRTI,
+										  InvalidAttrNumber,
+										  RECORDOID,
+										  -1,
+										  InvalidOid,
+										  0);
+			ntest->nulltesttype = src_null ? IS_NULL : IS_NOT_NULL;
+			ntest->argisrow = false;
+			ntest->location = -1;
+
+			/* Combine it with the action's WHEN condition */
+			if (action->qual == NULL)
+				action->qual = (Node *) ntest;
+			else
+				action->qual =
+					(Node *) makeBoolExpr(AND_EXPR,
+										  list_make2(ntest, action->qual),
+										  -1);
+		}
+
+		/*
 		 * Transform target lists for each INSERT and UPDATE action stmt
 		 */
 		switch (action->commandType)
diff --git a/src/backend/utils/misc/queryjumble.c b/src/backend/utils/misc/queryjumble.c
new file mode 100644
index 328995a..8e1baf9
--- a/src/backend/utils/misc/queryjumble.c
+++ b/src/backend/utils/misc/queryjumble.c
@@ -734,7 +734,7 @@ JumbleExpr(JumbleState *jstate, Node *no
 			{
 				MergeAction *mergeaction = (MergeAction *) node;
 
-				APP_JUMB(mergeaction->matched);
+				APP_JUMB(mergeaction->matchKind);
 				APP_JUMB(mergeaction->commandType);
 				JumbleExpr(jstate, mergeaction->qual);
 				JumbleExpr(jstate, (Node *) mergeaction->targetList);
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
new file mode 100644
index 23750ea..9b993f3
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -4216,17 +4216,35 @@ psql_completion(const char *text, int st
 			 TailMatches("USING", MatchAny, MatchAny, "ON", MatchAny, MatchAny, MatchAny, "WHEN"))
 		COMPLETE_WITH("MATCHED", "NOT MATCHED");
 
-	/* Complete ... WHEN [NOT] MATCHED with THEN/AND */
+	/*
+	 * Complete ... WHEN MATCHED and WHEN NOT MATCHED BY SOURCE|TARGET with
+	 * THEN/AND
+	 */
 	else if (TailMatches("WHEN", "MATCHED") ||
-			 TailMatches("WHEN", "NOT", "MATCHED"))
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE|TARGET"))
 		COMPLETE_WITH("THEN", "AND");
 
-	/* Complete ... WHEN MATCHED THEN with UPDATE SET/DELETE/DO NOTHING */
-	else if (TailMatches("WHEN", "MATCHED", "THEN"))
+	/* Complete ... WHEN NOT MATCHED with BY/THEN/AND */
+	else if (TailMatches("WHEN", "NOT", "MATCHED"))
+		COMPLETE_WITH("BY", "THEN", "AND");
+
+	/* Complete ... WHEN NOT MATCHED BY with SOURCE/TARGET */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "BY"))
+		COMPLETE_WITH("SOURCE", "TARGET");
+
+	/*
+	 * Complete ... WHEN MATCHED THEN and WHEN NOT MATCHED BY SOURCE THEN with
+	 * UPDATE SET/DELETE/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE", "THEN"))
 		COMPLETE_WITH("UPDATE SET", "DELETE", "DO NOTHING");
 
-	/* Complete ... WHEN NOT MATCHED THEN with INSERT/DO NOTHING */
-	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN"))
+	/*
+	 * Complete ... WHEN NOT MATCHED [BY TARGET] THEN with INSERT/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "TARGET", "THEN"))
 		COMPLETE_WITH("INSERT", "DO NOTHING");
 
 /* NOTIFY --- can be inside EXPLAIN, RULE, etc */
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
new file mode 100644
index cfeca96..c6617be
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -159,7 +159,6 @@ typedef struct Query
 								 * also USING clause for MERGE */
 
 	List	   *mergeActionList;	/* list of actions for MERGE (only) */
-	bool		mergeUseOuterJoin;	/* whether to use outer join */
 
 	List	   *targetList;		/* target list (of TargetEntry) */
 
@@ -1576,6 +1575,14 @@ typedef struct CommonTableExpr
 	 ((Query *) (cte)->ctequery)->targetList : \
 	 ((Query *) (cte)->ctequery)->returningList)
 
+/* MATCHED/NOT MATCHED specification for WHEN clauses in a MERGE statement */
+typedef enum MergeMatchKind
+{
+	MERGE_WHEN_MATCHED,
+	MERGE_WHEN_NOT_MATCHED_BY_SOURCE,
+	MERGE_WHEN_NOT_MATCHED_BY_TARGET
+} MergeMatchKind;
+
 /*
  * MergeWhenClause -
  *		raw parser representation of a WHEN clause in a MERGE statement
@@ -1585,7 +1592,7 @@ typedef struct CommonTableExpr
 typedef struct MergeWhenClause
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *condition;		/* WHEN conditions (raw parser) */
@@ -1601,7 +1608,7 @@ typedef struct MergeWhenClause
 typedef struct MergeAction
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *qual;			/* transformed WHEN conditions */
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
new file mode 100644
index bb36213..a398153
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -391,6 +391,7 @@ PG_KEYWORD("skip", SKIP, UNRESERVED_KEYW
 PG_KEYWORD("smallint", SMALLINT, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("snapshot", SNAPSHOT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("some", SOME, RESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("source", SOURCE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("sql", SQL_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("stable", STABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("standalone", STANDALONE_P, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -414,6 +415,7 @@ PG_KEYWORD("table", TABLE, RESERVED_KEYW
 PG_KEYWORD("tables", TABLES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablesample", TABLESAMPLE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablespace", TABLESPACE, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("target", TARGET, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temp", TEMP, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("template", TEMPLATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temporary", TEMPORARY, UNRESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/test/regress/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index 6c8a18f..5e15da2
--- a/src/test/regress/expected/merge.out
+++ b/src/test/regress/expected/merge.out
@@ -71,6 +71,15 @@ WHEN MATCHED THEN
 ERROR:  syntax error at or near "INSERT"
 LINE 5:  INSERT DEFAULT VALUES;
          ^
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
+ERROR:  syntax error at or near "INSERT"
+LINE 5:  INSERT DEFAULT VALUES;
+         ^
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -107,6 +116,15 @@ WHEN NOT MATCHED THEN
 ERROR:  syntax error at or near "UPDATE"
 LINE 5:  UPDATE SET balance = 0;
          ^
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
+ERROR:  syntax error at or near "UPDATE"
+LINE 5:  UPDATE SET balance = 0;
+         ^
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -271,6 +289,22 @@ SELECT * FROM target ORDER BY tid;
 (4 rows)
 
 ROLLBACK;
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   4 |      40
+(1 row)
+
+ROLLBACK;
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -738,6 +772,19 @@ SELECT * FROM wq_target;
    1 |      -1
 (1 row)
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+ERROR:  invalid reference to FROM-clause entry for table "s"
+LINE 3: WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+                                       ^
+DETAIL:  There is an entry for table "s", but it cannot be referenced from this part of the query.
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
  balance | sid 
@@ -923,6 +970,45 @@ SELECT * FROM target ORDER BY tid;
 (3 rows)
 
 ROLLBACK;
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE DELETE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  BEFORE INSERT ROW trigger row: (4,40)
+NOTICE:  BEFORE DELETE ROW trigger row: (2,20)
+NOTICE:  BEFORE UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  AFTER INSERT ROW trigger row: (4,40)
+NOTICE:  AFTER DELETE ROW trigger row: (2,20)
+NOTICE:  AFTER UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER DELETE STATEMENT trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |       0
+   3 |      10
+   4 |      40
+(3 rows)
+
+ROLLBACK;
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -1436,6 +1522,50 @@ WHEN NOT MATCHED AND s.a < 20 THEN
                ->  Seq Scan on ex_mtarget t (actual rows=49 loops=1)
 (12 rows)
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=54
+   ->  Merge Left Join (actual rows=54 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=100
+   ->  Merge Full Join (actual rows=100 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index 98fe104..19d9c1e
--- a/src/test/regress/sql/merge.sql
+++ b/src/test/regress/sql/merge.sql
@@ -51,6 +51,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN MATCHED THEN
 	INSERT DEFAULT VALUES;
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -75,6 +81,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN NOT MATCHED THEN
 	UPDATE SET balance = 0;
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -213,6 +225,18 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -497,6 +521,17 @@ WHEN NOT MATCHED AND s.balance = 100 THE
 	INSERT (tid) VALUES (s.sid);
 SELECT * FROM wq_target;
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
+
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
 MERGE INTO wq_target t
@@ -624,6 +659,25 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -916,6 +970,20 @@ WHEN MATCHED AND t.a >= 30 AND t.a <= 40
 WHEN NOT MATCHED AND s.a < 20 THEN
 	INSERT VALUES (a, b)');
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
new file mode 100644
index b87ad5c..1482ede
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -396,8 +396,8 @@
     originally matched appears later in the list of actions.
     On the other hand, if the row is concurrently updated or deleted so
     that the join condition fails, then <command>MERGE</command> will
-    evaluate the condition's <literal>NOT MATCHED</literal> actions next,
-    and execute the first one that succeeds.
+    evaluate the condition's <literal>NOT MATCHED [BY TARGET]</literal>
+    actions next, and execute the first one that succeeds.
     If <command>MERGE</command> attempts an <command>INSERT</command>
     and a unique index is present and a duplicate row is concurrently
     inserted, then a uniqueness violation error is raised;
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
new file mode 100644
index 0995fe0..8ef121a
--- a/doc/src/sgml/ref/merge.sgml
+++ b/doc/src/sgml/ref/merge.sgml
@@ -33,7 +33,8 @@ USING <replaceable class="parameter">dat
 <phrase>and <replaceable class="parameter">when_clause</replaceable> is:</phrase>
 
 { WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
-  WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
+  WHEN NOT MATCHED BY SOURCE [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
+  WHEN NOT MATCHED [BY TARGET] [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
 
 <phrase>and <replaceable class="parameter">merge_insert</replaceable> is:</phrase>
 
@@ -70,7 +71,9 @@ DELETE
    from <replaceable class="parameter">data_source</replaceable> to
    <replaceable class="parameter">target_table_name</replaceable>
    producing zero or more candidate change rows.  For each candidate change
-   row, the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal>
+   row, the status of <literal>MATCHED</literal>,
+   <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>
    is set just once, after which <literal>WHEN</literal> clauses are evaluated
    in the order specified.  For each candidate change row, the first clause to
    evaluate as true is executed.  No more than one <literal>WHEN</literal>
@@ -226,16 +229,37 @@ DELETE
       At least one <literal>WHEN</literal> clause is required.
      </para>
      <para>
+      The <literal>WHEN</literal> clause may specify <literal>WHEN MATCHED</literal>,
+      <literal>WHEN NOT MATCHED BY SOURCE</literal>, or
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>.
+      Note that the <acronym>SQL</acronym> standard only defines
+      <literal>WHEN MATCHED</literal> and <literal>WHEN NOT MATCHED</literal>
+      (which is defined to mean no matching target row).
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> is an extension to the
+      <acronym>SQL</acronym> standard, as is the option to append
+      <literal>BY TARGET</literal> to <literal>WHEN NOT MATCHED</literal>, to
+      make its meaning more explicit.
+     </para>
+     <para>
       If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
-      and the candidate change row matches a row in the
+      and the candidate change row matches a row in the source to a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
      </para>
      <para>
-      Conversely, if the <literal>WHEN</literal> clause specifies
-      <literal>WHEN NOT MATCHED</literal>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> and the candidate change
+      row represents a row in the
+      <replaceable class="parameter">target_table_name</replaceable> that does
+      not match a source row, the <literal>WHEN</literal> clause is executed
+      if the <replaceable class="parameter">condition</replaceable> is
+      absent or it evaluates to <literal>true</literal>.
+     </para>
+     <para>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>
       and the candidate change row does not match a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
@@ -257,7 +281,10 @@ DELETE
      <para>
       A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
       in both the source and the target relations. A condition on a
-      <literal>WHEN NOT MATCHED</literal> clause can only refer to columns from
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> clause can only refer to
+      columns from the target relation, since by definition there is no matching
+      source row. A condition on a <literal>WHEN NOT MATCHED [BY TARGET]</literal>
+      clause can only refer to columns from
       the source relation, since by definition there is no matching target row.
       Only the system attributes from the target table are accessible.
      </para>
@@ -382,8 +409,10 @@ DELETE
       <literal>WHEN MATCHED</literal> clause, the expression can use values
       from the original row in the target table, and values from the
       <literal>data_source</literal> row.
-      If used in a <literal>WHEN NOT MATCHED</literal> clause, the
-      expression can use values from the <literal>data_source</literal>.
+      If used in a <literal>WHEN NOT MATCHED BY SOURCE</literal> clause, the
+      expression can only use values from the original row in the target table.
+      If used in a <literal>WHEN NOT MATCHED [BY TARGET]</literal> clause, the
+      expression can only use values from the <literal>data_source</literal>.
      </para>
     </listitem>
    </varlistentry>
@@ -452,8 +481,9 @@ MERGE <replaceable class="parameter">tot
        <orderedlist>
         <listitem>
          <para>
-          Evaluate whether each row is <literal>MATCHED</literal> or
-          <literal>NOT MATCHED</literal>.
+          Evaluate whether each row is <literal>MATCHED</literal>,
+          <literal>NOT MATCHED BY SOURCE</literal>, or
+          <literal>NOT MATCHED [BY TARGET]</literal>.
          </para>
         </listitem>
         <listitem>
@@ -528,7 +558,8 @@ MERGE <replaceable class="parameter">tot
   <para>
    If a <literal>WHEN</literal> clause omits an <literal>AND</literal>
    sub-clause, it becomes the final reachable clause of that
-   kind (<literal>MATCHED</literal> or <literal>NOT MATCHED</literal>).
+   kind (<literal>MATCHED</literal>, <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>).
    If a later <literal>WHEN</literal> clause of that kind
    is specified it would be provably unreachable and an error is raised.
    If no final reachable clause is specified of either kind, it is
@@ -619,6 +650,23 @@ WHEN MATCHED THEN
    temporary table recently loaded into the database.
   </para>
 
+  <para>
+   Update <literal>wine</literal> based on a replacement wine list, inserting
+   rows for any new stock, updating modified stock entries, and deleting any
+   wines not present in the new list.
+<programlisting>
+MERGE INTO wines w
+USING new_wine_list s
+ON s.winename = w.winename
+WHEN NOT MATCHED BY TARGET THEN
+  INSERT VALUES(s.winename, s.stock)
+WHEN MATCHED AND w.stock != s.stock THEN
+  UPDATE SET stock = s.stock
+WHEN NOT MATCHED BY SOURCE THEN
+  DELETE;
+</programlisting>
+  </para>
+
  </refsect1>
 
  <refsect1>
@@ -627,7 +675,10 @@ WHEN MATCHED THEN
     This command conforms to the <acronym>SQL</acronym> standard.
   </para>
    <para>
-    The WITH clause and <literal>DO NOTHING</literal> action are extensions to
+    The WITH clause, <literal>BY SOURCE</literal> and
+    <literal>BY TARGET</literal> qualifiers to
+    <literal>WHEN NOT MATCHED</literal>, and
+    <literal>DO NOTHING</literal> action are extensions to
     the <acronym>SQL</acronym> standard.
   </para>
  </refsect1>
diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
new file mode 100644
index 651ad24..005da8d
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -898,8 +898,16 @@ ExecInitPartitionInfo(ModifyTableState *
 			action_state = makeNode(MergeActionState);
 			action_state->mas_action = action;
 
-			/* And put the action in the appropriate list */
-			if (action->matched)
+			/*
+			 * Put the action in the appropriate list.
+			 *
+			 * Note that the executor treats WHEN NOT MATCHED BY SOURCE
+			 * actions in exactly the same way as WHEN MATCHED actions, since
+			 * they both match the target (see ExecMerge).  Thus both types go
+			 * in the "matched" list.  Only WHEN NOT MATCHED BY TARGET actions
+			 * go in the "not matched" list.
+			 */
+			if (action->matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET)
 				list = &leaf_part_rri->ri_matchedMergeAction;
 			else
 				list = &leaf_part_rri->ri_notMatchedMergeAction;
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
new file mode 100644
index 687a542..339ba68
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -24,13 +24,15 @@
  *		values plus row-locating info for UPDATE and MERGE cases, or just the
  *		row-locating info for DELETE cases.
  *
- *		MERGE runs a join between the source relation and the target
- *		table; if any WHEN NOT MATCHED clauses are present, then the
- *		join is an outer join.  In this case, any unmatched tuples will
- *		have NULL row-locating info, and only INSERT can be run. But for
- *		matched tuples, then row-locating info is used to determine the
- *		tuple to UPDATE or DELETE. When all clauses are WHEN MATCHED,
- *		then an inner join is used, so all tuples contain row-locating info.
+ *		MERGE runs a join between the source relation and the target table.
+ *		If any WHEN NOT MATCHED [BY TARGET] clauses are present, then the join
+ *		is an outer join that might output tuples without a matching target
+ *		tuple.  In this case, any unmatched target tuples will have NULL
+ *		row-locating info, and only INSERT can be run.  But for matched
+ *		target tuples, the row-locating info is used to determine the tuple
+ *		to UPDATE or DELETE.  When all clauses are WHEN MATCHED or WHEN NOT
+ *		MATCHED BY SOURCE, all tuples produced by the join will include a
+ *		matching target tuple, so all tuples contain row-locating info.
  *
  *		If the query specifies RETURNING, then the ModifyTable returns a
  *		RETURNING tuple after completing each row insert, update, or delete.
@@ -2695,6 +2697,20 @@ ExecMerge(ModifyTableContext *context, R
 	bool		matched;
 
 	/*-----
+	 * Note that as far as the executor is concerned, WHEN NOT MATCHED BY
+	 * SOURCE actions are treated exactly the same as WHEN MATCHED actions,
+	 * since both match target tuples.  They are distinguished from one
+	 * another by a qual that tests if the source tuple is NULL, but the
+	 * executor knows nothing about the contents of the merge action quals.
+	 * Thus WHEN MATCHED and WHEN NOT MATCHED BY SOURCE actions are stored
+	 * together in the same "matched" list.  In the case of concurrent updates
+	 * and rechecks discussed below, the target tuple might be modified, but
+	 * not the source tuple, and so there is no danger of a WHEN MATCHED case
+	 * becoming a WHEN NOT MATCHED BY SOURCE case, or vice versa.  Thus, in
+	 * the dicussion that follows "MATCHED" means "matched by target", and
+	 * should be taken to include both WHEN MATCHED and WHEN NOT MATCHED BY
+	 * SOURCE, while "NOT MATCHED" means NOT MATCHED BY TARGET.
+	 *
 	 * If we are dealing with a WHEN MATCHED case (tupleid is valid), we
 	 * execute the first action for which the additional WHEN MATCHED AND
 	 * quals pass.  If an action without quals is found, that action is
@@ -3257,8 +3273,14 @@ ExecInitMerge(ModifyTableState *mtstate,
 			 * We create two lists - one for WHEN MATCHED actions and one for
 			 * WHEN NOT MATCHED actions - and stick the MergeActionState into
 			 * the appropriate list.
+			 *
+			 * Note that the executor treats WHEN NOT MATCHED BY SOURCE
+			 * actions in exactly the same way as WHEN MATCHED actions, since
+			 * they both match the target (see ExecMerge).  Thus both types go
+			 * in the "matched" list.  Only WHEN NOT MATCHED BY TARGET actions
+			 * go in the "not matched" list.
 			 */
-			if (action_state->mas_action->matched)
+			if (action->matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET)
 				list = &resultRelInfo->ri_matchedMergeAction;
 			else
 				list = &resultRelInfo->ri_notMatchedMergeAction;
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
new file mode 100644
index cfb314e..264fa3f
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -142,6 +142,9 @@ transform_MERGE_to_join(Query *parse)
 {
 	RangeTblEntry *joinrte;
 	JoinExpr   *joinexpr;
+	ListCell   *lc;
+	bool		src_only_tuples;
+	bool		tgt_only_tuples;
 	JoinType	jointype;
 	int			joinrti;
 	List	   *vars;
@@ -153,12 +156,32 @@ transform_MERGE_to_join(Query *parse)
 	vars = NIL;
 
 	/*
-	 * When any WHEN NOT MATCHED THEN INSERT clauses exist, we need to use an
-	 * outer join so that we process all unmatched tuples from the source
-	 * relation.  If none exist, we can use an inner join.
+	 * Work out what kind of join is required.  If there any WHEN NOT MATCHED
+	 * BY SOURCE/TARGET clauses, an outer join is required so that we process
+	 * all unmatched tuples from the source and/or target relations.
+	 * Otherwise, we can use an inner join.
 	 */
-	if (parse->mergeUseOuterJoin)
+	src_only_tuples = false;
+	tgt_only_tuples = false;
+	foreach(lc, parse->mergeActionList)
+	{
+		MergeAction *action = lfirst_node(MergeAction, lc);
+
+		if (action->commandType != CMD_NOTHING)
+		{
+			if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+				tgt_only_tuples = true;
+			if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_TARGET)
+				src_only_tuples = true;
+		}
+	}
+
+	if (src_only_tuples && tgt_only_tuples)
+		jointype = JOIN_FULL;
+	else if (src_only_tuples)
 		jointype = JOIN_RIGHT;
+	else if (tgt_only_tuples)
+		jointype = JOIN_LEFT;
 	else
 		jointype = JOIN_INNER;
 
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
new file mode 100644
index c6d747b..027d2be
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -157,15 +157,14 @@ preprocess_targetlist(PlannerInfo *root)
 			/*
 			 * Add resjunk entries for any Vars used in each action's
 			 * targetlist and WHEN condition that belong to relations other
-			 * than target.  Note that aggregates, window functions and
-			 * placeholder vars are not possible anywhere in MERGE's WHEN
-			 * clauses.  (PHVs may be added later, but they don't concern us
-			 * here.)
+			 * than target.  Note that aggregates and window functions are not
+			 * possible anywhere in MERGE's WHEN clauses, but PlaceHolderVars
+			 * may have been added by subquery pullup.
 			 */
 			vars = pull_var_clause((Node *)
 								   list_concat_copy((List *) action->qual,
 													action->targetList),
-								   0);
+								   PVC_INCLUDE_PLACEHOLDERS);
 			foreach(l2, vars)
 			{
 				Var		   *var = (Var *) lfirst(l2);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index a013838..dbe0089
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -273,6 +273,7 @@ static Node *makeRecursiveViewSelect(cha
 	struct SelectLimit *selectlimit;
 	SetQuantifier setquantifier;
 	struct GroupClause *groupclause;
+	MergeMatchKind mergematch;
 	MergeWhenClause *mergewhen;
 	struct KeyActions *keyactions;
 	struct KeyAction *keyaction;
@@ -512,6 +513,7 @@ static Node *makeRecursiveViewSelect(cha
 %type <onconflict> opt_on_conflict
 %type <mergewhen>	merge_insert merge_update merge_delete
 
+%type <mergematch> merge_when_tgt_matched merge_when_tgt_not_matched
 %type <node>	merge_when_clause opt_merge_when_condition
 %type <list>	merge_when_list
 
@@ -740,11 +742,11 @@ static Node *makeRecursiveViewSelect(cha
 
 	SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
-	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
+	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SOURCE SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRIP_P
 	SUBSCRIPTION SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
 
-	TABLE TABLES TABLESAMPLE TABLESPACE TEMP TEMPLATE TEMPORARY TEXT_P THEN
+	TABLE TABLES TABLESAMPLE TABLESPACE TARGET TEMP TEMPLATE TEMPORARY TEXT_P THEN
 	TIES TIME TIMESTAMP TO TRAILING TRANSACTION TRANSFORM
 	TREAT TRIGGER TRIM TRUE_P
 	TRUNCATE TRUSTED TYPE_P TYPES_P
@@ -12260,49 +12262,59 @@ merge_when_list:
 		;
 
 merge_when_clause:
-			WHEN MATCHED opt_merge_when_condition THEN merge_update
+			merge_when_tgt_matched opt_merge_when_condition THEN merge_update
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN merge_delete
+			| merge_when_tgt_matched opt_merge_when_condition THEN merge_delete
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN merge_insert
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN merge_insert
 				{
-					$6->matched = false;
-					$6->condition = $4;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $6;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = true;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $3;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = false;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $4;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
 		;
 
+merge_when_tgt_matched:
+			WHEN MATCHED					{ $$ = MERGE_WHEN_MATCHED; }
+			| WHEN NOT MATCHED BY SOURCE	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_SOURCE; }
+		;
+
+merge_when_tgt_not_matched:
+			WHEN NOT MATCHED				{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+			| WHEN NOT MATCHED BY TARGET	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+		;
+
 opt_merge_when_condition:
 			AND a_expr				{ $$ = $2; }
 			|						{ $$ = NULL; }
@@ -16961,6 +16973,7 @@ unreserved_keyword:
 			| SIMPLE
 			| SKIP
 			| SNAPSHOT
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -16979,6 +16992,7 @@ unreserved_keyword:
 			| SYSTEM_P
 			| TABLES
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
@@ -17555,6 +17569,7 @@ bare_label_keyword:
 			| SMALLINT
 			| SNAPSHOT
 			| SOME
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -17578,6 +17593,7 @@ bare_label_keyword:
 			| TABLES
 			| TABLESAMPLE
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
diff --git a/src/backend/parser/parse_merge.c b/src/backend/parser/parse_merge.c
new file mode 100644
index d886637..fca2bd9
--- a/src/backend/parser/parse_merge.c
+++ b/src/backend/parser/parse_merge.c
@@ -43,9 +43,9 @@ static void setNamespaceVisibilityForRTE
  * Make appropriate changes to the namespace visibility while transforming
  * individual action's quals and targetlist expressions. In particular, for
  * INSERT actions we must only see the source relation (since INSERT action is
- * invoked for NOT MATCHED tuples and hence there is no target tuple to deal
- * with). On the other hand, UPDATE and DELETE actions can see both source and
- * target relations.
+ * invoked for NOT MATCHED [BY TARGET] tuples and hence there is no target
+ * tuple to deal with). On the other hand, UPDATE and DELETE actions can see
+ * both source and target relations, unless invoked for NOT MATCH BY SOURCE.
  *
  * Also, since the internal join node can hide the source and target
  * relations, we must explicitly make the respective relation as visible so
@@ -61,7 +61,7 @@ setNamespaceForMergeWhen(ParseState *pst
 	targetRelRTE = rt_fetch(targetRTI, pstate->p_rtable);
 	sourceRelRTE = rt_fetch(sourceRTI, pstate->p_rtable);
 
-	if (mergeWhenClause->matched)
+	if (mergeWhenClause->matchKind == MERGE_WHEN_MATCHED)
 	{
 		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
 			   mergeWhenClause->commandType == CMD_DELETE ||
@@ -73,11 +73,25 @@ setNamespaceForMergeWhen(ParseState *pst
 		setNamespaceVisibilityForRTE(pstate->p_namespace,
 									 sourceRelRTE, true, true);
 	}
-	else
+	else if (mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
 	{
 		/*
-		 * NOT MATCHED actions can't see target relation, but they can see
-		 * source relation.
+		 * NOT MATCHED BY SOURCE actions can see the target relation, but they
+		 * can't see the source relation.
+		 */
+		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
+			   mergeWhenClause->commandType == CMD_DELETE ||
+			   mergeWhenClause->commandType == CMD_NOTHING);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 targetRelRTE, true, true);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 sourceRelRTE, false, false);
+	}
+	else	/* mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_TARGET */
+	{
+		/*
+		 * NOT MATCHED [BY TARGET] actions can't see target relation, but they
+		 * can see source relation.
 		 */
 		Assert(mergeWhenClause->commandType == CMD_INSERT ||
 			   mergeWhenClause->commandType == CMD_NOTHING);
@@ -98,7 +112,8 @@ transformMergeStmt(ParseState *pstate, M
 	Query	   *qry = makeNode(Query);
 	ListCell   *l;
 	AclMode		targetPerms = ACL_NO_RIGHTS;
-	bool		is_terminal[2];
+	bool		is_terminal[3];
+	bool		tgt_only_tuples;
 	Index		sourceRTI;
 	List	   *mergeActionList;
 	Node	   *joinExpr;
@@ -125,12 +140,13 @@ transformMergeStmt(ParseState *pstate, M
 	/*
 	 * Check WHEN clauses for permissions and sanity
 	 */
-	is_terminal[0] = false;
-	is_terminal[1] = false;
+	is_terminal[MERGE_WHEN_MATCHED] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
+	tgt_only_tuples = false;
 	foreach(l, stmt->mergeWhenClauses)
 	{
 		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
-		int			when_type = (mergeWhenClause->matched ? 0 : 1);
 
 		/*
 		 * Collect action types so we can check target permissions
@@ -155,12 +171,22 @@ transformMergeStmt(ParseState *pstate, M
 		/*
 		 * Check for unreachable WHEN clauses
 		 */
-		if (is_terminal[when_type])
+		if (is_terminal[mergeWhenClause->matchKind])
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
 					 errmsg("unreachable WHEN clause specified after unconditional WHEN clause")));
 		if (mergeWhenClause->condition == NULL)
-			is_terminal[when_type] = true;
+			is_terminal[mergeWhenClause->matchKind] = true;
+
+		/*
+		 * Test if we have a WHEN NOT MATCHED BY SOURCE action that processes
+		 * unmatched tuples from the target relation.  If so, additional WHEN
+		 * conditions are added below to differentiate the various match
+		 * kinds.
+		 */
+		if (mergeWhenClause->commandType != CMD_NOTHING &&
+			mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+			tgt_only_tuples = true;
 	}
 
 	/*
@@ -255,11 +281,7 @@ transformMergeStmt(ParseState *pstate, M
 
 		action = makeNode(MergeAction);
 		action->commandType = mergeWhenClause->commandType;
-		action->matched = mergeWhenClause->matched;
-
-		/* Use an outer join if any INSERT actions exist in the command. */
-		if (action->commandType == CMD_INSERT)
-			qry->mergeUseOuterJoin = true;
+		action->matchKind = mergeWhenClause->matchKind;
 
 		/*
 		 * Set namespace for the specific action. This must be done before
@@ -280,6 +302,51 @@ transformMergeStmt(ParseState *pstate, M
 											EXPR_KIND_MERGE_WHEN, "WHEN");
 
 		/*
+		 * If there any WHEN NOT MATCHED BY SOURCE actions that require
+		 * unmatched tuples from the target relation to be processed, add
+		 * additional WHEN conditions to every action to check that tuples
+		 * from the source match or do not match, as necessary.
+		 *
+		 * This distinguishes NOT MATCHED BY SOURCE actions (identified by a
+		 * "source IS NOT DISTINCT FROM NULL" clause) from MATCHED actions
+		 * (identified by a "source IS DISTINCT FROM NULL" clause).
+		 *
+		 * Additionally, a "source IS DISTINCT FROM NULL" clause is required
+		 * for NOT MATCHED [BY TARGET] actions in case the executor attempts
+		 * to invoke such an action for a concurrently deleted target row that
+		 * ends up matching neither source nor target.
+		 */
+		if (tgt_only_tuples)
+		{
+			bool		src_null;
+			NullTest   *ntest;
+
+			/* Make a "source IS [NOT] DISTINCT FROM NULL" clause */
+			src_null = action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE;
+
+			ntest = makeNode(NullTest);
+
+			ntest->arg = (Expr *) makeVar(sourceRTI,
+										  InvalidAttrNumber,
+										  RECORDOID,
+										  -1,
+										  InvalidOid,
+										  0);
+			ntest->nulltesttype = src_null ? IS_NULL : IS_NOT_NULL;
+			ntest->argisrow = false;
+			ntest->location = -1;
+
+			/* Combine it with the action's WHEN condition */
+			if (action->qual == NULL)
+				action->qual = (Node *) ntest;
+			else
+				action->qual =
+					(Node *) makeBoolExpr(AND_EXPR,
+										  list_make2(ntest, action->qual),
+										  -1);
+		}
+
+		/*
 		 * Transform target lists for each INSERT and UPDATE action stmt
 		 */
 		switch (action->commandType)
diff --git a/src/backend/utils/misc/queryjumble.c b/src/backend/utils/misc/queryjumble.c
new file mode 100644
index 328995a..8e1baf9
--- a/src/backend/utils/misc/queryjumble.c
+++ b/src/backend/utils/misc/queryjumble.c
@@ -734,7 +734,7 @@ JumbleExpr(JumbleState *jstate, Node *no
 			{
 				MergeAction *mergeaction = (MergeAction *) node;
 
-				APP_JUMB(mergeaction->matched);
+				APP_JUMB(mergeaction->matchKind);
 				APP_JUMB(mergeaction->commandType);
 				JumbleExpr(jstate, mergeaction->qual);
 				JumbleExpr(jstate, (Node *) mergeaction->targetList);
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
new file mode 100644
index 23750ea..9b993f3
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -4216,17 +4216,35 @@ psql_completion(const char *text, int st
 			 TailMatches("USING", MatchAny, MatchAny, "ON", MatchAny, MatchAny, MatchAny, "WHEN"))
 		COMPLETE_WITH("MATCHED", "NOT MATCHED");
 
-	/* Complete ... WHEN [NOT] MATCHED with THEN/AND */
+	/*
+	 * Complete ... WHEN MATCHED and WHEN NOT MATCHED BY SOURCE|TARGET with
+	 * THEN/AND
+	 */
 	else if (TailMatches("WHEN", "MATCHED") ||
-			 TailMatches("WHEN", "NOT", "MATCHED"))
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE|TARGET"))
 		COMPLETE_WITH("THEN", "AND");
 
-	/* Complete ... WHEN MATCHED THEN with UPDATE SET/DELETE/DO NOTHING */
-	else if (TailMatches("WHEN", "MATCHED", "THEN"))
+	/* Complete ... WHEN NOT MATCHED with BY/THEN/AND */
+	else if (TailMatches("WHEN", "NOT", "MATCHED"))
+		COMPLETE_WITH("BY", "THEN", "AND");
+
+	/* Complete ... WHEN NOT MATCHED BY with SOURCE/TARGET */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "BY"))
+		COMPLETE_WITH("SOURCE", "TARGET");
+
+	/*
+	 * Complete ... WHEN MATCHED THEN and WHEN NOT MATCHED BY SOURCE THEN with
+	 * UPDATE SET/DELETE/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE", "THEN"))
 		COMPLETE_WITH("UPDATE SET", "DELETE", "DO NOTHING");
 
-	/* Complete ... WHEN NOT MATCHED THEN with INSERT/DO NOTHING */
-	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN"))
+	/*
+	 * Complete ... WHEN NOT MATCHED [BY TARGET] THEN with INSERT/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "TARGET", "THEN"))
 		COMPLETE_WITH("INSERT", "DO NOTHING");
 
 /* NOTIFY --- can be inside EXPLAIN, RULE, etc */
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
new file mode 100644
index cfeca96..c6617be
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -159,7 +159,6 @@ typedef struct Query
 								 * also USING clause for MERGE */
 
 	List	   *mergeActionList;	/* list of actions for MERGE (only) */
-	bool		mergeUseOuterJoin;	/* whether to use outer join */
 
 	List	   *targetList;		/* target list (of TargetEntry) */
 
@@ -1576,6 +1575,14 @@ typedef struct CommonTableExpr
 	 ((Query *) (cte)->ctequery)->targetList : \
 	 ((Query *) (cte)->ctequery)->returningList)
 
+/* MATCHED/NOT MATCHED specification for WHEN clauses in a MERGE statement */
+typedef enum MergeMatchKind
+{
+	MERGE_WHEN_MATCHED,
+	MERGE_WHEN_NOT_MATCHED_BY_SOURCE,
+	MERGE_WHEN_NOT_MATCHED_BY_TARGET
+} MergeMatchKind;
+
 /*
  * MergeWhenClause -
  *		raw parser representation of a WHEN clause in a MERGE statement
@@ -1585,7 +1592,7 @@ typedef struct CommonTableExpr
 typedef struct MergeWhenClause
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *condition;		/* WHEN conditions (raw parser) */
@@ -1601,7 +1608,7 @@ typedef struct MergeWhenClause
 typedef struct MergeAction
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *qual;			/* transformed WHEN conditions */
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
new file mode 100644
index bb36213..a398153
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -391,6 +391,7 @@ PG_KEYWORD("skip", SKIP, UNRESERVED_KEYW
 PG_KEYWORD("smallint", SMALLINT, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("snapshot", SNAPSHOT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("some", SOME, RESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("source", SOURCE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("sql", SQL_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("stable", STABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("standalone", STANDALONE_P, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -414,6 +415,7 @@ PG_KEYWORD("table", TABLE, RESERVED_KEYW
 PG_KEYWORD("tables", TABLES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablesample", TABLESAMPLE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablespace", TABLESPACE, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("target", TARGET, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temp", TEMP, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("template", TEMPLATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temporary", TEMPORARY, UNRESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/test/regress/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index bc53b21..00cdbe9
--- a/src/test/regress/expected/merge.out
+++ b/src/test/regress/expected/merge.out
@@ -71,6 +71,15 @@ WHEN MATCHED THEN
 ERROR:  syntax error at or near "INSERT"
 LINE 5:  INSERT DEFAULT VALUES;
          ^
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
+ERROR:  syntax error at or near "INSERT"
+LINE 5:  INSERT DEFAULT VALUES;
+         ^
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -107,6 +116,15 @@ WHEN NOT MATCHED THEN
 ERROR:  syntax error at or near "UPDATE"
 LINE 5:  UPDATE SET balance = 0;
          ^
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
+ERROR:  syntax error at or near "UPDATE"
+LINE 5:  UPDATE SET balance = 0;
+         ^
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -271,6 +289,22 @@ SELECT * FROM target ORDER BY tid;
 (4 rows)
 
 ROLLBACK;
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   4 |      40
+(1 row)
+
+ROLLBACK;
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -738,6 +772,19 @@ SELECT * FROM wq_target;
    1 |      -1
 (1 row)
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+ERROR:  invalid reference to FROM-clause entry for table "s"
+LINE 3: WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+                                       ^
+DETAIL:  There is an entry for table "s", but it cannot be referenced from this part of the query.
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
  balance | sid 
@@ -923,6 +970,45 @@ SELECT * FROM target ORDER BY tid;
 (3 rows)
 
 ROLLBACK;
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE DELETE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  BEFORE INSERT ROW trigger row: (4,40)
+NOTICE:  BEFORE DELETE ROW trigger row: (2,20)
+NOTICE:  BEFORE UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  AFTER INSERT ROW trigger row: (4,40)
+NOTICE:  AFTER DELETE ROW trigger row: (2,20)
+NOTICE:  AFTER UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER DELETE STATEMENT trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |       0
+   3 |      10
+   4 |      40
+(3 rows)
+
+ROLLBACK;
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -1436,6 +1522,50 @@ WHEN NOT MATCHED AND s.a < 20 THEN
                ->  Seq Scan on ex_mtarget t (actual rows=49 loops=1)
 (12 rows)
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=54
+   ->  Merge Left Join (actual rows=54 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=100
+   ->  Merge Full Join (actual rows=100 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index fdbcd70..f5dfb2a
--- a/src/test/regress/sql/merge.sql
+++ b/src/test/regress/sql/merge.sql
@@ -51,6 +51,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN MATCHED THEN
 	INSERT DEFAULT VALUES;
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -75,6 +81,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN NOT MATCHED THEN
 	UPDATE SET balance = 0;
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -213,6 +225,18 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -497,6 +521,17 @@ WHEN NOT MATCHED AND s.balance = 100 THE
 	INSERT (tid) VALUES (s.sid);
 SELECT * FROM wq_target;
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
+
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
 MERGE INTO wq_target t
@@ -624,6 +659,25 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -916,6 +970,20 @@ WHEN MATCHED AND t.a >= 30 AND t.a <= 40
 WHEN NOT MATCHED AND s.a < 20 THEN
 	INSERT VALUES (a, b)');
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
new file mode 100644
index b87ad5c..1482ede
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -396,8 +396,8 @@
     originally matched appears later in the list of actions.
     On the other hand, if the row is concurrently updated or deleted so
     that the join condition fails, then <command>MERGE</command> will
-    evaluate the condition's <literal>NOT MATCHED</literal> actions next,
-    and execute the first one that succeeds.
+    evaluate the condition's <literal>NOT MATCHED [BY TARGET]</literal>
+    actions next, and execute the first one that succeeds.
     If <command>MERGE</command> attempts an <command>INSERT</command>
     and a unique index is present and a duplicate row is concurrently
     inserted, then a uniqueness violation error is raised;
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
new file mode 100644
index 0995fe0..8ef121a
--- a/doc/src/sgml/ref/merge.sgml
+++ b/doc/src/sgml/ref/merge.sgml
@@ -33,7 +33,8 @@ USING <replaceable class="parameter">dat
 <phrase>and <replaceable class="parameter">when_clause</replaceable> is:</phrase>
 
 { WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
-  WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
+  WHEN NOT MATCHED BY SOURCE [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
+  WHEN NOT MATCHED [BY TARGET] [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
 
 <phrase>and <replaceable class="parameter">merge_insert</replaceable> is:</phrase>
 
@@ -70,7 +71,9 @@ DELETE
    from <replaceable class="parameter">data_source</replaceable> to
    <replaceable class="parameter">target_table_name</replaceable>
    producing zero or more candidate change rows.  For each candidate change
-   row, the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal>
+   row, the status of <literal>MATCHED</literal>,
+   <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>
    is set just once, after which <literal>WHEN</literal> clauses are evaluated
    in the order specified.  For each candidate change row, the first clause to
    evaluate as true is executed.  No more than one <literal>WHEN</literal>
@@ -226,16 +229,37 @@ DELETE
       At least one <literal>WHEN</literal> clause is required.
      </para>
      <para>
+      The <literal>WHEN</literal> clause may specify <literal>WHEN MATCHED</literal>,
+      <literal>WHEN NOT MATCHED BY SOURCE</literal>, or
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>.
+      Note that the <acronym>SQL</acronym> standard only defines
+      <literal>WHEN MATCHED</literal> and <literal>WHEN NOT MATCHED</literal>
+      (which is defined to mean no matching target row).
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> is an extension to the
+      <acronym>SQL</acronym> standard, as is the option to append
+      <literal>BY TARGET</literal> to <literal>WHEN NOT MATCHED</literal>, to
+      make its meaning more explicit.
+     </para>
+     <para>
       If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
-      and the candidate change row matches a row in the
+      and the candidate change row matches a row in the source to a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
      </para>
      <para>
-      Conversely, if the <literal>WHEN</literal> clause specifies
-      <literal>WHEN NOT MATCHED</literal>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> and the candidate change
+      row represents a row in the
+      <replaceable class="parameter">target_table_name</replaceable> that does
+      not match a source row, the <literal>WHEN</literal> clause is executed
+      if the <replaceable class="parameter">condition</replaceable> is
+      absent or it evaluates to <literal>true</literal>.
+     </para>
+     <para>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>
       and the candidate change row does not match a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
@@ -257,7 +281,10 @@ DELETE
      <para>
       A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
       in both the source and the target relations. A condition on a
-      <literal>WHEN NOT MATCHED</literal> clause can only refer to columns from
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> clause can only refer to
+      columns from the target relation, since by definition there is no matching
+      source row. A condition on a <literal>WHEN NOT MATCHED [BY TARGET]</literal>
+      clause can only refer to columns from
       the source relation, since by definition there is no matching target row.
       Only the system attributes from the target table are accessible.
      </para>
@@ -382,8 +409,10 @@ DELETE
       <literal>WHEN MATCHED</literal> clause, the expression can use values
       from the original row in the target table, and values from the
       <literal>data_source</literal> row.
-      If used in a <literal>WHEN NOT MATCHED</literal> clause, the
-      expression can use values from the <literal>data_source</literal>.
+      If used in a <literal>WHEN NOT MATCHED BY SOURCE</literal> clause, the
+      expression can only use values from the original row in the target table.
+      If used in a <literal>WHEN NOT MATCHED [BY TARGET]</literal> clause, the
+      expression can only use values from the <literal>data_source</literal>.
      </para>
     </listitem>
    </varlistentry>
@@ -452,8 +481,9 @@ MERGE <replaceable class="parameter">tot
        <orderedlist>
         <listitem>
          <para>
-          Evaluate whether each row is <literal>MATCHED</literal> or
-          <literal>NOT MATCHED</literal>.
+          Evaluate whether each row is <literal>MATCHED</literal>,
+          <literal>NOT MATCHED BY SOURCE</literal>, or
+          <literal>NOT MATCHED [BY TARGET]</literal>.
          </para>
         </listitem>
         <listitem>
@@ -528,7 +558,8 @@ MERGE <replaceable class="parameter">tot
   <para>
    If a <literal>WHEN</literal> clause omits an <literal>AND</literal>
    sub-clause, it becomes the final reachable clause of that
-   kind (<literal>MATCHED</literal> or <literal>NOT MATCHED</literal>).
+   kind (<literal>MATCHED</literal>, <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>).
    If a later <literal>WHEN</literal> clause of that kind
    is specified it would be provably unreachable and an error is raised.
    If no final reachable clause is specified of either kind, it is
@@ -619,6 +650,23 @@ WHEN MATCHED THEN
    temporary table recently loaded into the database.
   </para>
 
+  <para>
+   Update <literal>wine</literal> based on a replacement wine list, inserting
+   rows for any new stock, updating modified stock entries, and deleting any
+   wines not present in the new list.
+<programlisting>
+MERGE INTO wines w
+USING new_wine_list s
+ON s.winename = w.winename
+WHEN NOT MATCHED BY TARGET THEN
+  INSERT VALUES(s.winename, s.stock)
+WHEN MATCHED AND w.stock != s.stock THEN
+  UPDATE SET stock = s.stock
+WHEN NOT MATCHED BY SOURCE THEN
+  DELETE;
+</programlisting>
+  </para>
+
  </refsect1>
 
  <refsect1>
@@ -627,7 +675,10 @@ WHEN MATCHED THEN
     This command conforms to the <acronym>SQL</acronym> standard.
   </para>
    <para>
-    The WITH clause and <literal>DO NOTHING</literal> action are extensions to
+    The WITH clause, <literal>BY SOURCE</literal> and
+    <literal>BY TARGET</literal> qualifiers to
+    <literal>WHEN NOT MATCHED</literal>, and
+    <literal>DO NOTHING</literal> action are extensions to
     the <acronym>SQL</acronym> standard.
   </para>
  </refsect1>
diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
new file mode 100644
index 651ad24..005da8d
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -898,8 +898,16 @@ ExecInitPartitionInfo(ModifyTableState *
 			action_state = makeNode(MergeActionState);
 			action_state->mas_action = action;
 
-			/* And put the action in the appropriate list */
-			if (action->matched)
+			/*
+			 * Put the action in the appropriate list.
+			 *
+			 * Note that the executor treats WHEN NOT MATCHED BY SOURCE
+			 * actions in exactly the same way as WHEN MATCHED actions, since
+			 * they both match the target (see ExecMerge).  Thus both types go
+			 * in the "matched" list.  Only WHEN NOT MATCHED BY TARGET actions
+			 * go in the "not matched" list.
+			 */
+			if (action->matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET)
 				list = &leaf_part_rri->ri_matchedMergeAction;
 			else
 				list = &leaf_part_rri->ri_notMatchedMergeAction;
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
new file mode 100644
index f419c47..d1f3a19
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -24,13 +24,15 @@
  *		values plus row-locating info for UPDATE and MERGE cases, or just the
  *		row-locating info for DELETE cases.
  *
- *		MERGE runs a join between the source relation and the target
- *		table; if any WHEN NOT MATCHED clauses are present, then the
- *		join is an outer join.  In this case, any unmatched tuples will
- *		have NULL row-locating info, and only INSERT can be run. But for
- *		matched tuples, then row-locating info is used to determine the
- *		tuple to UPDATE or DELETE. When all clauses are WHEN MATCHED,
- *		then an inner join is used, so all tuples contain row-locating info.
+ *		MERGE runs a join between the source relation and the target table.
+ *		If any WHEN NOT MATCHED [BY TARGET] clauses are present, then the join
+ *		is an outer join that might output tuples without a matching target
+ *		tuple.  In this case, any unmatched target tuples will have NULL
+ *		row-locating info, and only INSERT can be run.  But for matched
+ *		target tuples, the row-locating info is used to determine the tuple
+ *		to UPDATE or DELETE.  When all clauses are WHEN MATCHED or WHEN NOT
+ *		MATCHED BY SOURCE, all tuples produced by the join will include a
+ *		matching target tuple, so all tuples contain row-locating info.
  *
  *		If the query specifies RETURNING, then the ModifyTable returns a
  *		RETURNING tuple after completing each row insert, update, or delete.
@@ -2695,6 +2697,20 @@ ExecMerge(ModifyTableContext *context, R
 	bool		matched;
 
 	/*-----
+	 * Note that as far as the executor is concerned, WHEN NOT MATCHED BY
+	 * SOURCE actions are treated exactly the same as WHEN MATCHED actions,
+	 * since both match target tuples.  They are distinguished from one
+	 * another by a qual that tests if the source tuple is NULL, but the
+	 * executor knows nothing about the contents of the merge action quals.
+	 * Thus WHEN MATCHED and WHEN NOT MATCHED BY SOURCE actions are stored
+	 * together in the same "matched" list.  In the case of concurrent updates
+	 * and rechecks discussed below, the target tuple might be modified, but
+	 * not the source tuple, and so there is no danger of a WHEN MATCHED case
+	 * becoming a WHEN NOT MATCHED BY SOURCE case, or vice versa.  Thus, in
+	 * the dicussion that follows "MATCHED" means "matched by target", and
+	 * should be taken to include both WHEN MATCHED and WHEN NOT MATCHED BY
+	 * SOURCE, while "NOT MATCHED" means NOT MATCHED BY TARGET.
+	 *
 	 * If we are dealing with a WHEN MATCHED case (tupleid is valid), we
 	 * execute the first action for which the additional WHEN MATCHED AND
 	 * quals pass.  If an action without quals is found, that action is
@@ -3257,8 +3273,14 @@ ExecInitMerge(ModifyTableState *mtstate,
 			 * We create two lists - one for WHEN MATCHED actions and one for
 			 * WHEN NOT MATCHED actions - and stick the MergeActionState into
 			 * the appropriate list.
+			 *
+			 * Note that the executor treats WHEN NOT MATCHED BY SOURCE
+			 * actions in exactly the same way as WHEN MATCHED actions, since
+			 * they both match the target (see ExecMerge).  Thus both types go
+			 * in the "matched" list.  Only WHEN NOT MATCHED BY TARGET actions
+			 * go in the "not matched" list.
 			 */
-			if (action_state->mas_action->matched)
+			if (action->matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET)
 				list = &resultRelInfo->ri_matchedMergeAction;
 			else
 				list = &resultRelInfo->ri_notMatchedMergeAction;
diff --git a/src/backend/nodes/queryjumblefuncs.c b/src/backend/nodes/queryjumblefuncs.c
new file mode 100644
index 1608484..b380c3d
--- a/src/backend/nodes/queryjumblefuncs.c
+++ b/src/backend/nodes/queryjumblefuncs.c
@@ -734,7 +734,7 @@ JumbleExpr(JumbleState *jstate, Node *no
 			{
 				MergeAction *mergeaction = (MergeAction *) node;
 
-				APP_JUMB(mergeaction->matched);
+				APP_JUMB(mergeaction->matchKind);
 				APP_JUMB(mergeaction->commandType);
 				JumbleExpr(jstate, mergeaction->qual);
 				JumbleExpr(jstate, (Node *) mergeaction->targetList);
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
new file mode 100644
index 37a7af8..4f53f23
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -142,6 +142,9 @@ transform_MERGE_to_join(Query *parse)
 {
 	RangeTblEntry *joinrte;
 	JoinExpr   *joinexpr;
+	ListCell   *lc;
+	bool		src_only_tuples;
+	bool		tgt_only_tuples;
 	JoinType	jointype;
 	int			joinrti;
 	List	   *vars;
@@ -153,12 +156,32 @@ transform_MERGE_to_join(Query *parse)
 	vars = NIL;
 
 	/*
-	 * When any WHEN NOT MATCHED THEN INSERT clauses exist, we need to use an
-	 * outer join so that we process all unmatched tuples from the source
-	 * relation.  If none exist, we can use an inner join.
+	 * Work out what kind of join is required.  If there any WHEN NOT MATCHED
+	 * BY SOURCE/TARGET clauses, an outer join is required so that we process
+	 * all unmatched tuples from the source and/or target relations.
+	 * Otherwise, we can use an inner join.
 	 */
-	if (parse->mergeUseOuterJoin)
+	src_only_tuples = false;
+	tgt_only_tuples = false;
+	foreach(lc, parse->mergeActionList)
+	{
+		MergeAction *action = lfirst_node(MergeAction, lc);
+
+		if (action->commandType != CMD_NOTHING)
+		{
+			if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+				tgt_only_tuples = true;
+			if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_TARGET)
+				src_only_tuples = true;
+		}
+	}
+
+	if (src_only_tuples && tgt_only_tuples)
+		jointype = JOIN_FULL;
+	else if (src_only_tuples)
 		jointype = JOIN_RIGHT;
+	else if (tgt_only_tuples)
+		jointype = JOIN_LEFT;
 	else
 		jointype = JOIN_INNER;
 
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
new file mode 100644
index c6d747b..027d2be
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -157,15 +157,14 @@ preprocess_targetlist(PlannerInfo *root)
 			/*
 			 * Add resjunk entries for any Vars used in each action's
 			 * targetlist and WHEN condition that belong to relations other
-			 * than target.  Note that aggregates, window functions and
-			 * placeholder vars are not possible anywhere in MERGE's WHEN
-			 * clauses.  (PHVs may be added later, but they don't concern us
-			 * here.)
+			 * than target.  Note that aggregates and window functions are not
+			 * possible anywhere in MERGE's WHEN clauses, but PlaceHolderVars
+			 * may have been added by subquery pullup.
 			 */
 			vars = pull_var_clause((Node *)
 								   list_concat_copy((List *) action->qual,
 													action->targetList),
-								   0);
+								   PVC_INCLUDE_PLACEHOLDERS);
 			foreach(l2, vars)
 			{
 				Var		   *var = (Var *) lfirst(l2);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index a013838..dbe0089
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -273,6 +273,7 @@ static Node *makeRecursiveViewSelect(cha
 	struct SelectLimit *selectlimit;
 	SetQuantifier setquantifier;
 	struct GroupClause *groupclause;
+	MergeMatchKind mergematch;
 	MergeWhenClause *mergewhen;
 	struct KeyActions *keyactions;
 	struct KeyAction *keyaction;
@@ -512,6 +513,7 @@ static Node *makeRecursiveViewSelect(cha
 %type <onconflict> opt_on_conflict
 %type <mergewhen>	merge_insert merge_update merge_delete
 
+%type <mergematch> merge_when_tgt_matched merge_when_tgt_not_matched
 %type <node>	merge_when_clause opt_merge_when_condition
 %type <list>	merge_when_list
 
@@ -740,11 +742,11 @@ static Node *makeRecursiveViewSelect(cha
 
 	SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
-	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
+	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SOURCE SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRIP_P
 	SUBSCRIPTION SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
 
-	TABLE TABLES TABLESAMPLE TABLESPACE TEMP TEMPLATE TEMPORARY TEXT_P THEN
+	TABLE TABLES TABLESAMPLE TABLESPACE TARGET TEMP TEMPLATE TEMPORARY TEXT_P THEN
 	TIES TIME TIMESTAMP TO TRAILING TRANSACTION TRANSFORM
 	TREAT TRIGGER TRIM TRUE_P
 	TRUNCATE TRUSTED TYPE_P TYPES_P
@@ -12260,49 +12262,59 @@ merge_when_list:
 		;
 
 merge_when_clause:
-			WHEN MATCHED opt_merge_when_condition THEN merge_update
+			merge_when_tgt_matched opt_merge_when_condition THEN merge_update
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN merge_delete
+			| merge_when_tgt_matched opt_merge_when_condition THEN merge_delete
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN merge_insert
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN merge_insert
 				{
-					$6->matched = false;
-					$6->condition = $4;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $6;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = true;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $3;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = false;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $4;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
 		;
 
+merge_when_tgt_matched:
+			WHEN MATCHED					{ $$ = MERGE_WHEN_MATCHED; }
+			| WHEN NOT MATCHED BY SOURCE	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_SOURCE; }
+		;
+
+merge_when_tgt_not_matched:
+			WHEN NOT MATCHED				{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+			| WHEN NOT MATCHED BY TARGET	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+		;
+
 opt_merge_when_condition:
 			AND a_expr				{ $$ = $2; }
 			|						{ $$ = NULL; }
@@ -16961,6 +16973,7 @@ unreserved_keyword:
 			| SIMPLE
 			| SKIP
 			| SNAPSHOT
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -16979,6 +16992,7 @@ unreserved_keyword:
 			| SYSTEM_P
 			| TABLES
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
@@ -17555,6 +17569,7 @@ bare_label_keyword:
 			| SMALLINT
 			| SNAPSHOT
 			| SOME
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -17578,6 +17593,7 @@ bare_label_keyword:
 			| TABLES
 			| TABLESAMPLE
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
diff --git a/src/backend/parser/parse_merge.c b/src/backend/parser/parse_merge.c
new file mode 100644
index d886637..fca2bd9
--- a/src/backend/parser/parse_merge.c
+++ b/src/backend/parser/parse_merge.c
@@ -43,9 +43,9 @@ static void setNamespaceVisibilityForRTE
  * Make appropriate changes to the namespace visibility while transforming
  * individual action's quals and targetlist expressions. In particular, for
  * INSERT actions we must only see the source relation (since INSERT action is
- * invoked for NOT MATCHED tuples and hence there is no target tuple to deal
- * with). On the other hand, UPDATE and DELETE actions can see both source and
- * target relations.
+ * invoked for NOT MATCHED [BY TARGET] tuples and hence there is no target
+ * tuple to deal with). On the other hand, UPDATE and DELETE actions can see
+ * both source and target relations, unless invoked for NOT MATCH BY SOURCE.
  *
  * Also, since the internal join node can hide the source and target
  * relations, we must explicitly make the respective relation as visible so
@@ -61,7 +61,7 @@ setNamespaceForMergeWhen(ParseState *pst
 	targetRelRTE = rt_fetch(targetRTI, pstate->p_rtable);
 	sourceRelRTE = rt_fetch(sourceRTI, pstate->p_rtable);
 
-	if (mergeWhenClause->matched)
+	if (mergeWhenClause->matchKind == MERGE_WHEN_MATCHED)
 	{
 		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
 			   mergeWhenClause->commandType == CMD_DELETE ||
@@ -73,11 +73,25 @@ setNamespaceForMergeWhen(ParseState *pst
 		setNamespaceVisibilityForRTE(pstate->p_namespace,
 									 sourceRelRTE, true, true);
 	}
-	else
+	else if (mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
 	{
 		/*
-		 * NOT MATCHED actions can't see target relation, but they can see
-		 * source relation.
+		 * NOT MATCHED BY SOURCE actions can see the target relation, but they
+		 * can't see the source relation.
+		 */
+		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
+			   mergeWhenClause->commandType == CMD_DELETE ||
+			   mergeWhenClause->commandType == CMD_NOTHING);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 targetRelRTE, true, true);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 sourceRelRTE, false, false);
+	}
+	else	/* mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_TARGET */
+	{
+		/*
+		 * NOT MATCHED [BY TARGET] actions can't see target relation, but they
+		 * can see source relation.
 		 */
 		Assert(mergeWhenClause->commandType == CMD_INSERT ||
 			   mergeWhenClause->commandType == CMD_NOTHING);
@@ -98,7 +112,8 @@ transformMergeStmt(ParseState *pstate, M
 	Query	   *qry = makeNode(Query);
 	ListCell   *l;
 	AclMode		targetPerms = ACL_NO_RIGHTS;
-	bool		is_terminal[2];
+	bool		is_terminal[3];
+	bool		tgt_only_tuples;
 	Index		sourceRTI;
 	List	   *mergeActionList;
 	Node	   *joinExpr;
@@ -125,12 +140,13 @@ transformMergeStmt(ParseState *pstate, M
 	/*
 	 * Check WHEN clauses for permissions and sanity
 	 */
-	is_terminal[0] = false;
-	is_terminal[1] = false;
+	is_terminal[MERGE_WHEN_MATCHED] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
+	tgt_only_tuples = false;
 	foreach(l, stmt->mergeWhenClauses)
 	{
 		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
-		int			when_type = (mergeWhenClause->matched ? 0 : 1);
 
 		/*
 		 * Collect action types so we can check target permissions
@@ -155,12 +171,22 @@ transformMergeStmt(ParseState *pstate, M
 		/*
 		 * Check for unreachable WHEN clauses
 		 */
-		if (is_terminal[when_type])
+		if (is_terminal[mergeWhenClause->matchKind])
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
 					 errmsg("unreachable WHEN clause specified after unconditional WHEN clause")));
 		if (mergeWhenClause->condition == NULL)
-			is_terminal[when_type] = true;
+			is_terminal[mergeWhenClause->matchKind] = true;
+
+		/*
+		 * Test if we have a WHEN NOT MATCHED BY SOURCE action that processes
+		 * unmatched tuples from the target relation.  If so, additional WHEN
+		 * conditions are added below to differentiate the various match
+		 * kinds.
+		 */
+		if (mergeWhenClause->commandType != CMD_NOTHING &&
+			mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+			tgt_only_tuples = true;
 	}
 
 	/*
@@ -255,11 +281,7 @@ transformMergeStmt(ParseState *pstate, M
 
 		action = makeNode(MergeAction);
 		action->commandType = mergeWhenClause->commandType;
-		action->matched = mergeWhenClause->matched;
-
-		/* Use an outer join if any INSERT actions exist in the command. */
-		if (action->commandType == CMD_INSERT)
-			qry->mergeUseOuterJoin = true;
+		action->matchKind = mergeWhenClause->matchKind;
 
 		/*
 		 * Set namespace for the specific action. This must be done before
@@ -280,6 +302,51 @@ transformMergeStmt(ParseState *pstate, M
 											EXPR_KIND_MERGE_WHEN, "WHEN");
 
 		/*
+		 * If there any WHEN NOT MATCHED BY SOURCE actions that require
+		 * unmatched tuples from the target relation to be processed, add
+		 * additional WHEN conditions to every action to check that tuples
+		 * from the source match or do not match, as necessary.
+		 *
+		 * This distinguishes NOT MATCHED BY SOURCE actions (identified by a
+		 * "source IS NOT DISTINCT FROM NULL" clause) from MATCHED actions
+		 * (identified by a "source IS DISTINCT FROM NULL" clause).
+		 *
+		 * Additionally, a "source IS DISTINCT FROM NULL" clause is required
+		 * for NOT MATCHED [BY TARGET] actions in case the executor attempts
+		 * to invoke such an action for a concurrently deleted target row that
+		 * ends up matching neither source nor target.
+		 */
+		if (tgt_only_tuples)
+		{
+			bool		src_null;
+			NullTest   *ntest;
+
+			/* Make a "source IS [NOT] DISTINCT FROM NULL" clause */
+			src_null = action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE;
+
+			ntest = makeNode(NullTest);
+
+			ntest->arg = (Expr *) makeVar(sourceRTI,
+										  InvalidAttrNumber,
+										  RECORDOID,
+										  -1,
+										  InvalidOid,
+										  0);
+			ntest->nulltesttype = src_null ? IS_NULL : IS_NOT_NULL;
+			ntest->argisrow = false;
+			ntest->location = -1;
+
+			/* Combine it with the action's WHEN condition */
+			if (action->qual == NULL)
+				action->qual = (Node *) ntest;
+			else
+				action->qual =
+					(Node *) makeBoolExpr(AND_EXPR,
+										  list_make2(ntest, action->qual),
+										  -1);
+		}
+
+		/*
 		 * Transform target lists for each INSERT and UPDATE action stmt
 		 */
 		switch (action->commandType)
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
new file mode 100644
index 5e1882e..e202fcd
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -4237,17 +4237,35 @@ psql_completion(const char *text, int st
 			 TailMatches("USING", MatchAny, MatchAny, "ON", MatchAny, MatchAny, MatchAny, "WHEN"))
 		COMPLETE_WITH("MATCHED", "NOT MATCHED");
 
-	/* Complete ... WHEN [NOT] MATCHED with THEN/AND */
+	/*
+	 * Complete ... WHEN MATCHED and WHEN NOT MATCHED BY SOURCE|TARGET with
+	 * THEN/AND
+	 */
 	else if (TailMatches("WHEN", "MATCHED") ||
-			 TailMatches("WHEN", "NOT", "MATCHED"))
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE|TARGET"))
 		COMPLETE_WITH("THEN", "AND");
 
-	/* Complete ... WHEN MATCHED THEN with UPDATE SET/DELETE/DO NOTHING */
-	else if (TailMatches("WHEN", "MATCHED", "THEN"))
+	/* Complete ... WHEN NOT MATCHED with BY/THEN/AND */
+	else if (TailMatches("WHEN", "NOT", "MATCHED"))
+		COMPLETE_WITH("BY", "THEN", "AND");
+
+	/* Complete ... WHEN NOT MATCHED BY with SOURCE/TARGET */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "BY"))
+		COMPLETE_WITH("SOURCE", "TARGET");
+
+	/*
+	 * Complete ... WHEN MATCHED THEN and WHEN NOT MATCHED BY SOURCE THEN with
+	 * UPDATE SET/DELETE/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE", "THEN"))
 		COMPLETE_WITH("UPDATE SET", "DELETE", "DO NOTHING");
 
-	/* Complete ... WHEN NOT MATCHED THEN with INSERT/DO NOTHING */
-	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN"))
+	/*
+	 * Complete ... WHEN NOT MATCHED [BY TARGET] THEN with INSERT/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "TARGET", "THEN"))
 		COMPLETE_WITH("INSERT", "DO NOTHING");
 
 /* NOTIFY --- can be inside EXPLAIN, RULE, etc */
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
new file mode 100644
index 89335d9..b6a37f5
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -177,8 +177,6 @@ typedef struct Query
 								 * also USING clause for MERGE */
 
 	List	   *mergeActionList;	/* list of actions for MERGE (only) */
-	/* whether to use outer join */
-	bool		mergeUseOuterJoin;
 
 	List	   *targetList;		/* target list (of TargetEntry) */
 
@@ -1636,6 +1634,14 @@ typedef struct CommonTableExpr
 	 ((Query *) (cte)->ctequery)->targetList : \
 	 ((Query *) (cte)->ctequery)->returningList)
 
+/* MATCHED/NOT MATCHED specification for WHEN clauses in a MERGE statement */
+typedef enum MergeMatchKind
+{
+	MERGE_WHEN_MATCHED,
+	MERGE_WHEN_NOT_MATCHED_BY_SOURCE,
+	MERGE_WHEN_NOT_MATCHED_BY_TARGET
+} MergeMatchKind;
+
 /*
  * MergeWhenClause -
  *		raw parser representation of a WHEN clause in a MERGE statement
@@ -1645,7 +1651,7 @@ typedef struct CommonTableExpr
 typedef struct MergeWhenClause
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *condition;		/* WHEN conditions (raw parser) */
@@ -1661,7 +1667,7 @@ typedef struct MergeWhenClause
 typedef struct MergeAction
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	/* OVERRIDING clause */
 	OverridingKind override;
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
new file mode 100644
index bb36213..a398153
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -391,6 +391,7 @@ PG_KEYWORD("skip", SKIP, UNRESERVED_KEYW
 PG_KEYWORD("smallint", SMALLINT, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("snapshot", SNAPSHOT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("some", SOME, RESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("source", SOURCE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("sql", SQL_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("stable", STABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("standalone", STANDALONE_P, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -414,6 +415,7 @@ PG_KEYWORD("table", TABLE, RESERVED_KEYW
 PG_KEYWORD("tables", TABLES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablesample", TABLESAMPLE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablespace", TABLESPACE, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("target", TARGET, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temp", TEMP, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("template", TEMPLATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temporary", TEMPORARY, UNRESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/test/regress/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index bc53b21..00cdbe9
--- a/src/test/regress/expected/merge.out
+++ b/src/test/regress/expected/merge.out
@@ -71,6 +71,15 @@ WHEN MATCHED THEN
 ERROR:  syntax error at or near "INSERT"
 LINE 5:  INSERT DEFAULT VALUES;
          ^
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
+ERROR:  syntax error at or near "INSERT"
+LINE 5:  INSERT DEFAULT VALUES;
+         ^
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -107,6 +116,15 @@ WHEN NOT MATCHED THEN
 ERROR:  syntax error at or near "UPDATE"
 LINE 5:  UPDATE SET balance = 0;
          ^
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
+ERROR:  syntax error at or near "UPDATE"
+LINE 5:  UPDATE SET balance = 0;
+         ^
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -271,6 +289,22 @@ SELECT * FROM target ORDER BY tid;
 (4 rows)
 
 ROLLBACK;
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   4 |      40
+(1 row)
+
+ROLLBACK;
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -738,6 +772,19 @@ SELECT * FROM wq_target;
    1 |      -1
 (1 row)
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+ERROR:  invalid reference to FROM-clause entry for table "s"
+LINE 3: WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+                                       ^
+DETAIL:  There is an entry for table "s", but it cannot be referenced from this part of the query.
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
  balance | sid 
@@ -923,6 +970,45 @@ SELECT * FROM target ORDER BY tid;
 (3 rows)
 
 ROLLBACK;
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE DELETE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  BEFORE INSERT ROW trigger row: (4,40)
+NOTICE:  BEFORE DELETE ROW trigger row: (2,20)
+NOTICE:  BEFORE UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  AFTER INSERT ROW trigger row: (4,40)
+NOTICE:  AFTER DELETE ROW trigger row: (2,20)
+NOTICE:  AFTER UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER DELETE STATEMENT trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |       0
+   3 |      10
+   4 |      40
+(3 rows)
+
+ROLLBACK;
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -1436,6 +1522,50 @@ WHEN NOT MATCHED AND s.a < 20 THEN
                ->  Seq Scan on ex_mtarget t (actual rows=49 loops=1)
 (12 rows)
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=54
+   ->  Merge Left Join (actual rows=54 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=100
+   ->  Merge Full Join (actual rows=100 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index fdbcd70..f5dfb2a
--- a/src/test/regress/sql/merge.sql
+++ b/src/test/regress/sql/merge.sql
@@ -51,6 +51,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN MATCHED THEN
 	INSERT DEFAULT VALUES;
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -75,6 +81,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN NOT MATCHED THEN
 	UPDATE SET balance = 0;
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -213,6 +225,18 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -497,6 +521,17 @@ WHEN NOT MATCHED AND s.balance = 100 THE
 	INSERT (tid) VALUES (s.sid);
 SELECT * FROM wq_target;
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
+
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
 MERGE INTO wq_target t
@@ -624,6 +659,25 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -916,6 +970,20 @@ WHEN MATCHED AND t.a >= 30 AND t.a <= 40
 WHEN NOT MATCHED AND s.a < 20 THEN
 	INSERT VALUES (a, b)');
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
new file mode 100644
index b87ad5c..1482ede
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -396,8 +396,8 @@
     originally matched appears later in the list of actions.
     On the other hand, if the row is concurrently updated or deleted so
     that the join condition fails, then <command>MERGE</command> will
-    evaluate the condition's <literal>NOT MATCHED</literal> actions next,
-    and execute the first one that succeeds.
+    evaluate the condition's <literal>NOT MATCHED [BY TARGET]</literal>
+    actions next, and execute the first one that succeeds.
     If <command>MERGE</command> attempts an <command>INSERT</command>
     and a unique index is present and a duplicate row is concurrently
     inserted, then a uniqueness violation error is raised;
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
new file mode 100644
index 0995fe0..8ef121a
--- a/doc/src/sgml/ref/merge.sgml
+++ b/doc/src/sgml/ref/merge.sgml
@@ -33,7 +33,8 @@ USING <replaceable class="parameter">dat
 <phrase>and <replaceable class="parameter">when_clause</replaceable> is:</phrase>
 
 { WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
-  WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
+  WHEN NOT MATCHED BY SOURCE [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
+  WHEN NOT MATCHED [BY TARGET] [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
 
 <phrase>and <replaceable class="parameter">merge_insert</replaceable> is:</phrase>
 
@@ -70,7 +71,9 @@ DELETE
    from <replaceable class="parameter">data_source</replaceable> to
    <replaceable class="parameter">target_table_name</replaceable>
    producing zero or more candidate change rows.  For each candidate change
-   row, the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal>
+   row, the status of <literal>MATCHED</literal>,
+   <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>
    is set just once, after which <literal>WHEN</literal> clauses are evaluated
    in the order specified.  For each candidate change row, the first clause to
    evaluate as true is executed.  No more than one <literal>WHEN</literal>
@@ -226,16 +229,37 @@ DELETE
       At least one <literal>WHEN</literal> clause is required.
      </para>
      <para>
+      The <literal>WHEN</literal> clause may specify <literal>WHEN MATCHED</literal>,
+      <literal>WHEN NOT MATCHED BY SOURCE</literal>, or
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>.
+      Note that the <acronym>SQL</acronym> standard only defines
+      <literal>WHEN MATCHED</literal> and <literal>WHEN NOT MATCHED</literal>
+      (which is defined to mean no matching target row).
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> is an extension to the
+      <acronym>SQL</acronym> standard, as is the option to append
+      <literal>BY TARGET</literal> to <literal>WHEN NOT MATCHED</literal>, to
+      make its meaning more explicit.
+     </para>
+     <para>
       If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
-      and the candidate change row matches a row in the
+      and the candidate change row matches a row in the source to a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
      </para>
      <para>
-      Conversely, if the <literal>WHEN</literal> clause specifies
-      <literal>WHEN NOT MATCHED</literal>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> and the candidate change
+      row represents a row in the
+      <replaceable class="parameter">target_table_name</replaceable> that does
+      not match a source row, the <literal>WHEN</literal> clause is executed
+      if the <replaceable class="parameter">condition</replaceable> is
+      absent or it evaluates to <literal>true</literal>.
+     </para>
+     <para>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>
       and the candidate change row does not match a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
@@ -257,7 +281,10 @@ DELETE
      <para>
       A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
       in both the source and the target relations. A condition on a
-      <literal>WHEN NOT MATCHED</literal> clause can only refer to columns from
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> clause can only refer to
+      columns from the target relation, since by definition there is no matching
+      source row. A condition on a <literal>WHEN NOT MATCHED [BY TARGET]</literal>
+      clause can only refer to columns from
       the source relation, since by definition there is no matching target row.
       Only the system attributes from the target table are accessible.
      </para>
@@ -382,8 +409,10 @@ DELETE
       <literal>WHEN MATCHED</literal> clause, the expression can use values
       from the original row in the target table, and values from the
       <literal>data_source</literal> row.
-      If used in a <literal>WHEN NOT MATCHED</literal> clause, the
-      expression can use values from the <literal>data_source</literal>.
+      If used in a <literal>WHEN NOT MATCHED BY SOURCE</literal> clause, the
+      expression can only use values from the original row in the target table.
+      If used in a <literal>WHEN NOT MATCHED [BY TARGET]</literal> clause, the
+      expression can only use values from the <literal>data_source</literal>.
      </para>
     </listitem>
    </varlistentry>
@@ -452,8 +481,9 @@ MERGE <replaceable class="parameter">tot
        <orderedlist>
         <listitem>
          <para>
-          Evaluate whether each row is <literal>MATCHED</literal> or
-          <literal>NOT MATCHED</literal>.
+          Evaluate whether each row is <literal>MATCHED</literal>,
+          <literal>NOT MATCHED BY SOURCE</literal>, or
+          <literal>NOT MATCHED [BY TARGET]</literal>.
          </para>
         </listitem>
         <listitem>
@@ -528,7 +558,8 @@ MERGE <replaceable class="parameter">tot
   <para>
    If a <literal>WHEN</literal> clause omits an <literal>AND</literal>
    sub-clause, it becomes the final reachable clause of that
-   kind (<literal>MATCHED</literal> or <literal>NOT MATCHED</literal>).
+   kind (<literal>MATCHED</literal>, <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>).
    If a later <literal>WHEN</literal> clause of that kind
    is specified it would be provably unreachable and an error is raised.
    If no final reachable clause is specified of either kind, it is
@@ -619,6 +650,23 @@ WHEN MATCHED THEN
    temporary table recently loaded into the database.
   </para>
 
+  <para>
+   Update <literal>wine</literal> based on a replacement wine list, inserting
+   rows for any new stock, updating modified stock entries, and deleting any
+   wines not present in the new list.
+<programlisting>
+MERGE INTO wines w
+USING new_wine_list s
+ON s.winename = w.winename
+WHEN NOT MATCHED BY TARGET THEN
+  INSERT VALUES(s.winename, s.stock)
+WHEN MATCHED AND w.stock != s.stock THEN
+  UPDATE SET stock = s.stock
+WHEN NOT MATCHED BY SOURCE THEN
+  DELETE;
+</programlisting>
+  </para>
+
  </refsect1>
 
  <refsect1>
@@ -627,7 +675,10 @@ WHEN MATCHED THEN
     This command conforms to the <acronym>SQL</acronym> standard.
   </para>
    <para>
-    The WITH clause and <literal>DO NOTHING</literal> action are extensions to
+    The WITH clause, <literal>BY SOURCE</literal> and
+    <literal>BY TARGET</literal> qualifiers to
+    <literal>WHEN NOT MATCHED</literal>, and
+    <literal>DO NOTHING</literal> action are extensions to
     the <acronym>SQL</acronym> standard.
   </para>
  </refsect1>
diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
new file mode 100644
index 651ad24..005da8d
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -898,8 +898,16 @@ ExecInitPartitionInfo(ModifyTableState *
 			action_state = makeNode(MergeActionState);
 			action_state->mas_action = action;
 
-			/* And put the action in the appropriate list */
-			if (action->matched)
+			/*
+			 * Put the action in the appropriate list.
+			 *
+			 * Note that the executor treats WHEN NOT MATCHED BY SOURCE
+			 * actions in exactly the same way as WHEN MATCHED actions, since
+			 * they both match the target (see ExecMerge).  Thus both types go
+			 * in the "matched" list.  Only WHEN NOT MATCHED BY TARGET actions
+			 * go in the "not matched" list.
+			 */
+			if (action->matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET)
 				list = &leaf_part_rri->ri_matchedMergeAction;
 			else
 				list = &leaf_part_rri->ri_notMatchedMergeAction;
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
new file mode 100644
index 1ac6517..5384406
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -24,13 +24,15 @@
  *		values plus row-locating info for UPDATE and MERGE cases, or just the
  *		row-locating info for DELETE cases.
  *
- *		MERGE runs a join between the source relation and the target
- *		table; if any WHEN NOT MATCHED clauses are present, then the
- *		join is an outer join.  In this case, any unmatched tuples will
- *		have NULL row-locating info, and only INSERT can be run. But for
- *		matched tuples, then row-locating info is used to determine the
- *		tuple to UPDATE or DELETE. When all clauses are WHEN MATCHED,
- *		then an inner join is used, so all tuples contain row-locating info.
+ *		MERGE runs a join between the source relation and the target table.
+ *		If any WHEN NOT MATCHED [BY TARGET] clauses are present, then the join
+ *		is an outer join that might output tuples without a matching target
+ *		tuple.  In this case, any unmatched target tuples will have NULL
+ *		row-locating info, and only INSERT can be run.  But for matched
+ *		target tuples, the row-locating info is used to determine the tuple
+ *		to UPDATE or DELETE.  When all clauses are WHEN MATCHED or WHEN NOT
+ *		MATCHED BY SOURCE, all tuples produced by the join will include a
+ *		matching target tuple, so all tuples contain row-locating info.
  *
  *		If the query specifies RETURNING, then the ModifyTable returns a
  *		RETURNING tuple after completing each row insert, update, or delete.
@@ -2695,6 +2697,20 @@ ExecMerge(ModifyTableContext *context, R
 	bool		matched;
 
 	/*-----
+	 * Note that as far as the executor is concerned, WHEN NOT MATCHED BY
+	 * SOURCE actions are treated exactly the same as WHEN MATCHED actions,
+	 * since both match target tuples.  They are distinguished from one
+	 * another by a qual that tests if the source tuple is NULL, but the
+	 * executor knows nothing about the contents of the merge action quals.
+	 * Thus WHEN MATCHED and WHEN NOT MATCHED BY SOURCE actions are stored
+	 * together in the same "matched" list.  In the case of concurrent updates
+	 * and rechecks discussed below, the target tuple might be modified, but
+	 * not the source tuple, and so there is no danger of a WHEN MATCHED case
+	 * becoming a WHEN NOT MATCHED BY SOURCE case, or vice versa.  Thus, in
+	 * the dicussion that follows "MATCHED" means "matched by target", and
+	 * should be taken to include both WHEN MATCHED and WHEN NOT MATCHED BY
+	 * SOURCE, while "NOT MATCHED" means NOT MATCHED BY TARGET.
+	 *
 	 * If we are dealing with a WHEN MATCHED case (tupleid is valid), we
 	 * execute the first action for which the additional WHEN MATCHED AND
 	 * quals pass.  If an action without quals is found, that action is
@@ -3257,8 +3273,14 @@ ExecInitMerge(ModifyTableState *mtstate,
 			 * We create two lists - one for WHEN MATCHED actions and one for
 			 * WHEN NOT MATCHED actions - and stick the MergeActionState into
 			 * the appropriate list.
+			 *
+			 * Note that the executor treats WHEN NOT MATCHED BY SOURCE
+			 * actions in exactly the same way as WHEN MATCHED actions, since
+			 * they both match the target (see ExecMerge).  Thus both types go
+			 * in the "matched" list.  Only WHEN NOT MATCHED BY TARGET actions
+			 * go in the "not matched" list.
 			 */
-			if (action_state->mas_action->matched)
+			if (action->matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET)
 				list = &resultRelInfo->ri_matchedMergeAction;
 			else
 				list = &resultRelInfo->ri_notMatchedMergeAction;
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
new file mode 100644
index 870d84b..3b32c8d
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -153,6 +153,9 @@ transform_MERGE_to_join(Query *parse)
 {
 	RangeTblEntry *joinrte;
 	JoinExpr   *joinexpr;
+	ListCell   *lc;
+	bool		src_only_tuples;
+	bool		tgt_only_tuples;
 	JoinType	jointype;
 	int			joinrti;
 	List	   *vars;
@@ -164,12 +167,32 @@ transform_MERGE_to_join(Query *parse)
 	vars = NIL;
 
 	/*
-	 * When any WHEN NOT MATCHED THEN INSERT clauses exist, we need to use an
-	 * outer join so that we process all unmatched tuples from the source
-	 * relation.  If none exist, we can use an inner join.
+	 * Work out what kind of join is required.  If there any WHEN NOT MATCHED
+	 * BY SOURCE/TARGET clauses, an outer join is required so that we process
+	 * all unmatched tuples from the source and/or target relations.
+	 * Otherwise, we can use an inner join.
 	 */
-	if (parse->mergeUseOuterJoin)
+	src_only_tuples = false;
+	tgt_only_tuples = false;
+	foreach(lc, parse->mergeActionList)
+	{
+		MergeAction *action = lfirst_node(MergeAction, lc);
+
+		if (action->commandType != CMD_NOTHING)
+		{
+			if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+				tgt_only_tuples = true;
+			if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_TARGET)
+				src_only_tuples = true;
+		}
+	}
+
+	if (src_only_tuples && tgt_only_tuples)
+		jointype = JOIN_FULL;
+	else if (src_only_tuples)
 		jointype = JOIN_RIGHT;
+	else if (tgt_only_tuples)
+		jointype = JOIN_LEFT;
 	else
 		jointype = JOIN_INNER;
 
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
new file mode 100644
index c6d747b..027d2be
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -157,15 +157,14 @@ preprocess_targetlist(PlannerInfo *root)
 			/*
 			 * Add resjunk entries for any Vars used in each action's
 			 * targetlist and WHEN condition that belong to relations other
-			 * than target.  Note that aggregates, window functions and
-			 * placeholder vars are not possible anywhere in MERGE's WHEN
-			 * clauses.  (PHVs may be added later, but they don't concern us
-			 * here.)
+			 * than target.  Note that aggregates and window functions are not
+			 * possible anywhere in MERGE's WHEN clauses, but PlaceHolderVars
+			 * may have been added by subquery pullup.
 			 */
 			vars = pull_var_clause((Node *)
 								   list_concat_copy((List *) action->qual,
 													action->targetList),
-								   0);
+								   PVC_INCLUDE_PLACEHOLDERS);
 			foreach(l2, vars)
 			{
 				Var		   *var = (Var *) lfirst(l2);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index a013838..dbe0089
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -273,6 +273,7 @@ static Node *makeRecursiveViewSelect(cha
 	struct SelectLimit *selectlimit;
 	SetQuantifier setquantifier;
 	struct GroupClause *groupclause;
+	MergeMatchKind mergematch;
 	MergeWhenClause *mergewhen;
 	struct KeyActions *keyactions;
 	struct KeyAction *keyaction;
@@ -512,6 +513,7 @@ static Node *makeRecursiveViewSelect(cha
 %type <onconflict> opt_on_conflict
 %type <mergewhen>	merge_insert merge_update merge_delete
 
+%type <mergematch> merge_when_tgt_matched merge_when_tgt_not_matched
 %type <node>	merge_when_clause opt_merge_when_condition
 %type <list>	merge_when_list
 
@@ -740,11 +742,11 @@ static Node *makeRecursiveViewSelect(cha
 
 	SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
-	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
+	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SOURCE SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRIP_P
 	SUBSCRIPTION SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
 
-	TABLE TABLES TABLESAMPLE TABLESPACE TEMP TEMPLATE TEMPORARY TEXT_P THEN
+	TABLE TABLES TABLESAMPLE TABLESPACE TARGET TEMP TEMPLATE TEMPORARY TEXT_P THEN
 	TIES TIME TIMESTAMP TO TRAILING TRANSACTION TRANSFORM
 	TREAT TRIGGER TRIM TRUE_P
 	TRUNCATE TRUSTED TYPE_P TYPES_P
@@ -12260,49 +12262,59 @@ merge_when_list:
 		;
 
 merge_when_clause:
-			WHEN MATCHED opt_merge_when_condition THEN merge_update
+			merge_when_tgt_matched opt_merge_when_condition THEN merge_update
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN merge_delete
+			| merge_when_tgt_matched opt_merge_when_condition THEN merge_delete
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN merge_insert
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN merge_insert
 				{
-					$6->matched = false;
-					$6->condition = $4;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $6;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = true;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $3;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = false;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $4;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
 		;
 
+merge_when_tgt_matched:
+			WHEN MATCHED					{ $$ = MERGE_WHEN_MATCHED; }
+			| WHEN NOT MATCHED BY SOURCE	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_SOURCE; }
+		;
+
+merge_when_tgt_not_matched:
+			WHEN NOT MATCHED				{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+			| WHEN NOT MATCHED BY TARGET	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+		;
+
 opt_merge_when_condition:
 			AND a_expr				{ $$ = $2; }
 			|						{ $$ = NULL; }
@@ -16961,6 +16973,7 @@ unreserved_keyword:
 			| SIMPLE
 			| SKIP
 			| SNAPSHOT
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -16979,6 +16992,7 @@ unreserved_keyword:
 			| SYSTEM_P
 			| TABLES
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
@@ -17555,6 +17569,7 @@ bare_label_keyword:
 			| SMALLINT
 			| SNAPSHOT
 			| SOME
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -17578,6 +17593,7 @@ bare_label_keyword:
 			| TABLES
 			| TABLESAMPLE
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
diff --git a/src/backend/parser/parse_merge.c b/src/backend/parser/parse_merge.c
new file mode 100644
index d886637..fca2bd9
--- a/src/backend/parser/parse_merge.c
+++ b/src/backend/parser/parse_merge.c
@@ -43,9 +43,9 @@ static void setNamespaceVisibilityForRTE
  * Make appropriate changes to the namespace visibility while transforming
  * individual action's quals and targetlist expressions. In particular, for
  * INSERT actions we must only see the source relation (since INSERT action is
- * invoked for NOT MATCHED tuples and hence there is no target tuple to deal
- * with). On the other hand, UPDATE and DELETE actions can see both source and
- * target relations.
+ * invoked for NOT MATCHED [BY TARGET] tuples and hence there is no target
+ * tuple to deal with). On the other hand, UPDATE and DELETE actions can see
+ * both source and target relations, unless invoked for NOT MATCH BY SOURCE.
  *
  * Also, since the internal join node can hide the source and target
  * relations, we must explicitly make the respective relation as visible so
@@ -61,7 +61,7 @@ setNamespaceForMergeWhen(ParseState *pst
 	targetRelRTE = rt_fetch(targetRTI, pstate->p_rtable);
 	sourceRelRTE = rt_fetch(sourceRTI, pstate->p_rtable);
 
-	if (mergeWhenClause->matched)
+	if (mergeWhenClause->matchKind == MERGE_WHEN_MATCHED)
 	{
 		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
 			   mergeWhenClause->commandType == CMD_DELETE ||
@@ -73,11 +73,25 @@ setNamespaceForMergeWhen(ParseState *pst
 		setNamespaceVisibilityForRTE(pstate->p_namespace,
 									 sourceRelRTE, true, true);
 	}
-	else
+	else if (mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
 	{
 		/*
-		 * NOT MATCHED actions can't see target relation, but they can see
-		 * source relation.
+		 * NOT MATCHED BY SOURCE actions can see the target relation, but they
+		 * can't see the source relation.
+		 */
+		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
+			   mergeWhenClause->commandType == CMD_DELETE ||
+			   mergeWhenClause->commandType == CMD_NOTHING);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 targetRelRTE, true, true);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 sourceRelRTE, false, false);
+	}
+	else	/* mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_TARGET */
+	{
+		/*
+		 * NOT MATCHED [BY TARGET] actions can't see target relation, but they
+		 * can see source relation.
 		 */
 		Assert(mergeWhenClause->commandType == CMD_INSERT ||
 			   mergeWhenClause->commandType == CMD_NOTHING);
@@ -98,7 +112,8 @@ transformMergeStmt(ParseState *pstate, M
 	Query	   *qry = makeNode(Query);
 	ListCell   *l;
 	AclMode		targetPerms = ACL_NO_RIGHTS;
-	bool		is_terminal[2];
+	bool		is_terminal[3];
+	bool		tgt_only_tuples;
 	Index		sourceRTI;
 	List	   *mergeActionList;
 	Node	   *joinExpr;
@@ -125,12 +140,13 @@ transformMergeStmt(ParseState *pstate, M
 	/*
 	 * Check WHEN clauses for permissions and sanity
 	 */
-	is_terminal[0] = false;
-	is_terminal[1] = false;
+	is_terminal[MERGE_WHEN_MATCHED] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
+	tgt_only_tuples = false;
 	foreach(l, stmt->mergeWhenClauses)
 	{
 		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
-		int			when_type = (mergeWhenClause->matched ? 0 : 1);
 
 		/*
 		 * Collect action types so we can check target permissions
@@ -155,12 +171,22 @@ transformMergeStmt(ParseState *pstate, M
 		/*
 		 * Check for unreachable WHEN clauses
 		 */
-		if (is_terminal[when_type])
+		if (is_terminal[mergeWhenClause->matchKind])
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
 					 errmsg("unreachable WHEN clause specified after unconditional WHEN clause")));
 		if (mergeWhenClause->condition == NULL)
-			is_terminal[when_type] = true;
+			is_terminal[mergeWhenClause->matchKind] = true;
+
+		/*
+		 * Test if we have a WHEN NOT MATCHED BY SOURCE action that processes
+		 * unmatched tuples from the target relation.  If so, additional WHEN
+		 * conditions are added below to differentiate the various match
+		 * kinds.
+		 */
+		if (mergeWhenClause->commandType != CMD_NOTHING &&
+			mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+			tgt_only_tuples = true;
 	}
 
 	/*
@@ -255,11 +281,7 @@ transformMergeStmt(ParseState *pstate, M
 
 		action = makeNode(MergeAction);
 		action->commandType = mergeWhenClause->commandType;
-		action->matched = mergeWhenClause->matched;
-
-		/* Use an outer join if any INSERT actions exist in the command. */
-		if (action->commandType == CMD_INSERT)
-			qry->mergeUseOuterJoin = true;
+		action->matchKind = mergeWhenClause->matchKind;
 
 		/*
 		 * Set namespace for the specific action. This must be done before
@@ -280,6 +302,51 @@ transformMergeStmt(ParseState *pstate, M
 											EXPR_KIND_MERGE_WHEN, "WHEN");
 
 		/*
+		 * If there any WHEN NOT MATCHED BY SOURCE actions that require
+		 * unmatched tuples from the target relation to be processed, add
+		 * additional WHEN conditions to every action to check that tuples
+		 * from the source match or do not match, as necessary.
+		 *
+		 * This distinguishes NOT MATCHED BY SOURCE actions (identified by a
+		 * "source IS NOT DISTINCT FROM NULL" clause) from MATCHED actions
+		 * (identified by a "source IS DISTINCT FROM NULL" clause).
+		 *
+		 * Additionally, a "source IS DISTINCT FROM NULL" clause is required
+		 * for NOT MATCHED [BY TARGET] actions in case the executor attempts
+		 * to invoke such an action for a concurrently deleted target row that
+		 * ends up matching neither source nor target.
+		 */
+		if (tgt_only_tuples)
+		{
+			bool		src_null;
+			NullTest   *ntest;
+
+			/* Make a "source IS [NOT] DISTINCT FROM NULL" clause */
+			src_null = action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE;
+
+			ntest = makeNode(NullTest);
+
+			ntest->arg = (Expr *) makeVar(sourceRTI,
+										  InvalidAttrNumber,
+										  RECORDOID,
+										  -1,
+										  InvalidOid,
+										  0);
+			ntest->nulltesttype = src_null ? IS_NULL : IS_NOT_NULL;
+			ntest->argisrow = false;
+			ntest->location = -1;
+
+			/* Combine it with the action's WHEN condition */
+			if (action->qual == NULL)
+				action->qual = (Node *) ntest;
+			else
+				action->qual =
+					(Node *) makeBoolExpr(AND_EXPR,
+										  list_make2(ntest, action->qual),
+										  -1);
+		}
+
+		/*
 		 * Transform target lists for each INSERT and UPDATE action stmt
 		 */
 		switch (action->commandType)
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
new file mode 100644
index 5e1882e..e202fcd
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -4237,17 +4237,35 @@ psql_completion(const char *text, int st
 			 TailMatches("USING", MatchAny, MatchAny, "ON", MatchAny, MatchAny, MatchAny, "WHEN"))
 		COMPLETE_WITH("MATCHED", "NOT MATCHED");
 
-	/* Complete ... WHEN [NOT] MATCHED with THEN/AND */
+	/*
+	 * Complete ... WHEN MATCHED and WHEN NOT MATCHED BY SOURCE|TARGET with
+	 * THEN/AND
+	 */
 	else if (TailMatches("WHEN", "MATCHED") ||
-			 TailMatches("WHEN", "NOT", "MATCHED"))
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE|TARGET"))
 		COMPLETE_WITH("THEN", "AND");
 
-	/* Complete ... WHEN MATCHED THEN with UPDATE SET/DELETE/DO NOTHING */
-	else if (TailMatches("WHEN", "MATCHED", "THEN"))
+	/* Complete ... WHEN NOT MATCHED with BY/THEN/AND */
+	else if (TailMatches("WHEN", "NOT", "MATCHED"))
+		COMPLETE_WITH("BY", "THEN", "AND");
+
+	/* Complete ... WHEN NOT MATCHED BY with SOURCE/TARGET */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "BY"))
+		COMPLETE_WITH("SOURCE", "TARGET");
+
+	/*
+	 * Complete ... WHEN MATCHED THEN and WHEN NOT MATCHED BY SOURCE THEN with
+	 * UPDATE SET/DELETE/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE", "THEN"))
 		COMPLETE_WITH("UPDATE SET", "DELETE", "DO NOTHING");
 
-	/* Complete ... WHEN NOT MATCHED THEN with INSERT/DO NOTHING */
-	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN"))
+	/*
+	 * Complete ... WHEN NOT MATCHED [BY TARGET] THEN with INSERT/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "TARGET", "THEN"))
 		COMPLETE_WITH("INSERT", "DO NOTHING");
 
 /* NOTIFY --- can be inside EXPLAIN, RULE, etc */
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
new file mode 100644
index 855da99..d9d3a18
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -184,8 +184,6 @@ typedef struct Query
 								 * also USING clause for MERGE */
 
 	List	   *mergeActionList;	/* list of actions for MERGE (only) */
-	/* whether to use outer join */
-	bool		mergeUseOuterJoin pg_node_attr(query_jumble_ignore);
 
 	List	   *targetList;		/* target list (of TargetEntry) */
 
@@ -1662,6 +1660,14 @@ typedef struct CommonTableExpr
 	 ((Query *) (cte)->ctequery)->targetList : \
 	 ((Query *) (cte)->ctequery)->returningList)
 
+/* MATCHED/NOT MATCHED specification for WHEN clauses in a MERGE statement */
+typedef enum MergeMatchKind
+{
+	MERGE_WHEN_MATCHED,
+	MERGE_WHEN_NOT_MATCHED_BY_SOURCE,
+	MERGE_WHEN_NOT_MATCHED_BY_TARGET
+} MergeMatchKind;
+
 /*
  * MergeWhenClause -
  *		raw parser representation of a WHEN clause in a MERGE statement
@@ -1671,7 +1677,7 @@ typedef struct CommonTableExpr
 typedef struct MergeWhenClause
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *condition;		/* WHEN conditions (raw parser) */
@@ -1687,7 +1693,7 @@ typedef struct MergeWhenClause
 typedef struct MergeAction
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	/* OVERRIDING clause */
 	OverridingKind override pg_node_attr(query_jumble_ignore);
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
new file mode 100644
index bb36213..a398153
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -391,6 +391,7 @@ PG_KEYWORD("skip", SKIP, UNRESERVED_KEYW
 PG_KEYWORD("smallint", SMALLINT, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("snapshot", SNAPSHOT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("some", SOME, RESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("source", SOURCE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("sql", SQL_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("stable", STABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("standalone", STANDALONE_P, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -414,6 +415,7 @@ PG_KEYWORD("table", TABLE, RESERVED_KEYW
 PG_KEYWORD("tables", TABLES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablesample", TABLESAMPLE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablespace", TABLESPACE, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("target", TARGET, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temp", TEMP, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("template", TEMPLATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temporary", TEMPORARY, UNRESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/test/regress/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index bc53b21..00cdbe9
--- a/src/test/regress/expected/merge.out
+++ b/src/test/regress/expected/merge.out
@@ -71,6 +71,15 @@ WHEN MATCHED THEN
 ERROR:  syntax error at or near "INSERT"
 LINE 5:  INSERT DEFAULT VALUES;
          ^
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
+ERROR:  syntax error at or near "INSERT"
+LINE 5:  INSERT DEFAULT VALUES;
+         ^
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -107,6 +116,15 @@ WHEN NOT MATCHED THEN
 ERROR:  syntax error at or near "UPDATE"
 LINE 5:  UPDATE SET balance = 0;
          ^
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
+ERROR:  syntax error at or near "UPDATE"
+LINE 5:  UPDATE SET balance = 0;
+         ^
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -271,6 +289,22 @@ SELECT * FROM target ORDER BY tid;
 (4 rows)
 
 ROLLBACK;
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   4 |      40
+(1 row)
+
+ROLLBACK;
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -738,6 +772,19 @@ SELECT * FROM wq_target;
    1 |      -1
 (1 row)
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+ERROR:  invalid reference to FROM-clause entry for table "s"
+LINE 3: WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+                                       ^
+DETAIL:  There is an entry for table "s", but it cannot be referenced from this part of the query.
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
  balance | sid 
@@ -923,6 +970,45 @@ SELECT * FROM target ORDER BY tid;
 (3 rows)
 
 ROLLBACK;
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE DELETE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  BEFORE INSERT ROW trigger row: (4,40)
+NOTICE:  BEFORE DELETE ROW trigger row: (2,20)
+NOTICE:  BEFORE UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  AFTER INSERT ROW trigger row: (4,40)
+NOTICE:  AFTER DELETE ROW trigger row: (2,20)
+NOTICE:  AFTER UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER DELETE STATEMENT trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |       0
+   3 |      10
+   4 |      40
+(3 rows)
+
+ROLLBACK;
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -1436,6 +1522,50 @@ WHEN NOT MATCHED AND s.a < 20 THEN
                ->  Seq Scan on ex_mtarget t (actual rows=49 loops=1)
 (12 rows)
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=54
+   ->  Merge Left Join (actual rows=54 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=100
+   ->  Merge Full Join (actual rows=100 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index fdbcd70..f5dfb2a
--- a/src/test/regress/sql/merge.sql
+++ b/src/test/regress/sql/merge.sql
@@ -51,6 +51,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN MATCHED THEN
 	INSERT DEFAULT VALUES;
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -75,6 +81,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN NOT MATCHED THEN
 	UPDATE SET balance = 0;
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -213,6 +225,18 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -497,6 +521,17 @@ WHEN NOT MATCHED AND s.balance = 100 THE
 	INSERT (tid) VALUES (s.sid);
 SELECT * FROM wq_target;
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
+
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
 MERGE INTO wq_target t
@@ -624,6 +659,25 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -916,6 +970,20 @@ WHEN MATCHED AND t.a >= 30 AND t.a <= 40
 WHEN NOT MATCHED AND s.a < 20 THEN
 	INSERT VALUES (a, b)');
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
new file mode 100644
index b87ad5c..1482ede
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -396,8 +396,8 @@
     originally matched appears later in the list of actions.
     On the other hand, if the row is concurrently updated or deleted so
     that the join condition fails, then <command>MERGE</command> will
-    evaluate the condition's <literal>NOT MATCHED</literal> actions next,
-    and execute the first one that succeeds.
+    evaluate the condition's <literal>NOT MATCHED [BY TARGET]</literal>
+    actions next, and execute the first one that succeeds.
     If <command>MERGE</command> attempts an <command>INSERT</command>
     and a unique index is present and a duplicate row is concurrently
     inserted, then a uniqueness violation error is raised;
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
new file mode 100644
index 0995fe0..8ef121a
--- a/doc/src/sgml/ref/merge.sgml
+++ b/doc/src/sgml/ref/merge.sgml
@@ -33,7 +33,8 @@ USING <replaceable class="parameter">dat
 <phrase>and <replaceable class="parameter">when_clause</replaceable> is:</phrase>
 
 { WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
-  WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
+  WHEN NOT MATCHED BY SOURCE [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
+  WHEN NOT MATCHED [BY TARGET] [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
 
 <phrase>and <replaceable class="parameter">merge_insert</replaceable> is:</phrase>
 
@@ -70,7 +71,9 @@ DELETE
    from <replaceable class="parameter">data_source</replaceable> to
    <replaceable class="parameter">target_table_name</replaceable>
    producing zero or more candidate change rows.  For each candidate change
-   row, the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal>
+   row, the status of <literal>MATCHED</literal>,
+   <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>
    is set just once, after which <literal>WHEN</literal> clauses are evaluated
    in the order specified.  For each candidate change row, the first clause to
    evaluate as true is executed.  No more than one <literal>WHEN</literal>
@@ -226,16 +229,37 @@ DELETE
       At least one <literal>WHEN</literal> clause is required.
      </para>
      <para>
+      The <literal>WHEN</literal> clause may specify <literal>WHEN MATCHED</literal>,
+      <literal>WHEN NOT MATCHED BY SOURCE</literal>, or
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>.
+      Note that the <acronym>SQL</acronym> standard only defines
+      <literal>WHEN MATCHED</literal> and <literal>WHEN NOT MATCHED</literal>
+      (which is defined to mean no matching target row).
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> is an extension to the
+      <acronym>SQL</acronym> standard, as is the option to append
+      <literal>BY TARGET</literal> to <literal>WHEN NOT MATCHED</literal>, to
+      make its meaning more explicit.
+     </para>
+     <para>
       If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
-      and the candidate change row matches a row in the
+      and the candidate change row matches a row in the source to a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
      </para>
      <para>
-      Conversely, if the <literal>WHEN</literal> clause specifies
-      <literal>WHEN NOT MATCHED</literal>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> and the candidate change
+      row represents a row in the
+      <replaceable class="parameter">target_table_name</replaceable> that does
+      not match a source row, the <literal>WHEN</literal> clause is executed
+      if the <replaceable class="parameter">condition</replaceable> is
+      absent or it evaluates to <literal>true</literal>.
+     </para>
+     <para>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>
       and the candidate change row does not match a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
@@ -257,7 +281,10 @@ DELETE
      <para>
       A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
       in both the source and the target relations. A condition on a
-      <literal>WHEN NOT MATCHED</literal> clause can only refer to columns from
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> clause can only refer to
+      columns from the target relation, since by definition there is no matching
+      source row. A condition on a <literal>WHEN NOT MATCHED [BY TARGET]</literal>
+      clause can only refer to columns from
       the source relation, since by definition there is no matching target row.
       Only the system attributes from the target table are accessible.
      </para>
@@ -382,8 +409,10 @@ DELETE
       <literal>WHEN MATCHED</literal> clause, the expression can use values
       from the original row in the target table, and values from the
       <literal>data_source</literal> row.
-      If used in a <literal>WHEN NOT MATCHED</literal> clause, the
-      expression can use values from the <literal>data_source</literal>.
+      If used in a <literal>WHEN NOT MATCHED BY SOURCE</literal> clause, the
+      expression can only use values from the original row in the target table.
+      If used in a <literal>WHEN NOT MATCHED [BY TARGET]</literal> clause, the
+      expression can only use values from the <literal>data_source</literal>.
      </para>
     </listitem>
    </varlistentry>
@@ -452,8 +481,9 @@ MERGE <replaceable class="parameter">tot
        <orderedlist>
         <listitem>
          <para>
-          Evaluate whether each row is <literal>MATCHED</literal> or
-          <literal>NOT MATCHED</literal>.
+          Evaluate whether each row is <literal>MATCHED</literal>,
+          <literal>NOT MATCHED BY SOURCE</literal>, or
+          <literal>NOT MATCHED [BY TARGET]</literal>.
          </para>
         </listitem>
         <listitem>
@@ -528,7 +558,8 @@ MERGE <replaceable class="parameter">tot
   <para>
    If a <literal>WHEN</literal> clause omits an <literal>AND</literal>
    sub-clause, it becomes the final reachable clause of that
-   kind (<literal>MATCHED</literal> or <literal>NOT MATCHED</literal>).
+   kind (<literal>MATCHED</literal>, <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>).
    If a later <literal>WHEN</literal> clause of that kind
    is specified it would be provably unreachable and an error is raised.
    If no final reachable clause is specified of either kind, it is
@@ -619,6 +650,23 @@ WHEN MATCHED THEN
    temporary table recently loaded into the database.
   </para>
 
+  <para>
+   Update <literal>wine</literal> based on a replacement wine list, inserting
+   rows for any new stock, updating modified stock entries, and deleting any
+   wines not present in the new list.
+<programlisting>
+MERGE INTO wines w
+USING new_wine_list s
+ON s.winename = w.winename
+WHEN NOT MATCHED BY TARGET THEN
+  INSERT VALUES(s.winename, s.stock)
+WHEN MATCHED AND w.stock != s.stock THEN
+  UPDATE SET stock = s.stock
+WHEN NOT MATCHED BY SOURCE THEN
+  DELETE;
+</programlisting>
+  </para>
+
  </refsect1>
 
  <refsect1>
@@ -627,7 +675,10 @@ WHEN MATCHED THEN
     This command conforms to the <acronym>SQL</acronym> standard.
   </para>
    <para>
-    The WITH clause and <literal>DO NOTHING</literal> action are extensions to
+    The WITH clause, <literal>BY SOURCE</literal> and
+    <literal>BY TARGET</literal> qualifiers to
+    <literal>WHEN NOT MATCHED</literal>, and
+    <literal>DO NOTHING</literal> action are extensions to
     the <acronym>SQL</acronym> standard.
   </para>
  </refsect1>
diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
new file mode 100644
index fd6ca8a..861d35e
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -902,8 +902,16 @@ ExecInitPartitionInfo(ModifyTableState *
 			action_state = makeNode(MergeActionState);
 			action_state->mas_action = action;
 
-			/* And put the action in the appropriate list */
-			if (action->matched)
+			/*
+			 * Put the action in the appropriate list.
+			 *
+			 * Note that the executor treats WHEN NOT MATCHED BY SOURCE
+			 * actions in exactly the same way as WHEN MATCHED actions, since
+			 * they both match the target (see ExecMerge).  Thus both types go
+			 * in the "matched" list.  Only WHEN NOT MATCHED BY TARGET actions
+			 * go in the "not matched" list.
+			 */
+			if (action->matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET)
 				list = &leaf_part_rri->ri_matchedMergeAction;
 			else
 				list = &leaf_part_rri->ri_notMatchedMergeAction;
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
new file mode 100644
index 3fa2b93..a1307f8
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -24,13 +24,15 @@
  *		values plus row-locating info for UPDATE and MERGE cases, or just the
  *		row-locating info for DELETE cases.
  *
- *		MERGE runs a join between the source relation and the target
- *		table; if any WHEN NOT MATCHED clauses are present, then the
- *		join is an outer join.  In this case, any unmatched tuples will
- *		have NULL row-locating info, and only INSERT can be run. But for
- *		matched tuples, then row-locating info is used to determine the
- *		tuple to UPDATE or DELETE. When all clauses are WHEN MATCHED,
- *		then an inner join is used, so all tuples contain row-locating info.
+ *		MERGE runs a join between the source relation and the target table.
+ *		If any WHEN NOT MATCHED [BY TARGET] clauses are present, then the join
+ *		is an outer join that might output tuples without a matching target
+ *		tuple.  In this case, any unmatched target tuples will have NULL
+ *		row-locating info, and only INSERT can be run.  But for matched
+ *		target tuples, the row-locating info is used to determine the tuple
+ *		to UPDATE or DELETE.  When all clauses are WHEN MATCHED or WHEN NOT
+ *		MATCHED BY SOURCE, all tuples produced by the join will include a
+ *		matching target tuple, so all tuples contain row-locating info.
  *
  *		If the query specifies RETURNING, then the ModifyTable returns a
  *		RETURNING tuple after completing each row insert, update, or delete.
@@ -2706,6 +2708,20 @@ ExecMerge(ModifyTableContext *context, R
 	bool		matched;
 
 	/*-----
+	 * Note that as far as the executor is concerned, WHEN NOT MATCHED BY
+	 * SOURCE actions are treated exactly the same as WHEN MATCHED actions,
+	 * since both match target tuples.  They are distinguished from one
+	 * another by a qual that tests if the source tuple is NULL, but the
+	 * executor knows nothing about the contents of the merge action quals.
+	 * Thus WHEN MATCHED and WHEN NOT MATCHED BY SOURCE actions are stored
+	 * together in the same "matched" list.  In the case of concurrent updates
+	 * and rechecks discussed below, the target tuple might be modified, but
+	 * not the source tuple, and so there is no danger of a WHEN MATCHED case
+	 * becoming a WHEN NOT MATCHED BY SOURCE case, or vice versa.  Thus, in
+	 * the dicussion that follows "MATCHED" means "matched by target", and
+	 * should be taken to include both WHEN MATCHED and WHEN NOT MATCHED BY
+	 * SOURCE, while "NOT MATCHED" means NOT MATCHED BY TARGET.
+	 *
 	 * If we are dealing with a WHEN MATCHED case (tupleid is valid), we
 	 * execute the first action for which the additional WHEN MATCHED AND
 	 * quals pass.  If an action without quals is found, that action is
@@ -3242,8 +3258,14 @@ ExecInitMerge(ModifyTableState *mtstate,
 			 * We create two lists - one for WHEN MATCHED actions and one for
 			 * WHEN NOT MATCHED actions - and stick the MergeActionState into
 			 * the appropriate list.
+			 *
+			 * Note that the executor treats WHEN NOT MATCHED BY SOURCE
+			 * actions in exactly the same way as WHEN MATCHED actions, since
+			 * they both match the target (see ExecMerge).  Thus both types go
+			 * in the "matched" list.  Only WHEN NOT MATCHED BY TARGET actions
+			 * go in the "not matched" list.
 			 */
-			if (action_state->mas_action->matched)
+			if (action->matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET)
 				list = &resultRelInfo->ri_matchedMergeAction;
 			else
 				list = &resultRelInfo->ri_notMatchedMergeAction;
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
new file mode 100644
index 870d84b..3b32c8d
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -153,6 +153,9 @@ transform_MERGE_to_join(Query *parse)
 {
 	RangeTblEntry *joinrte;
 	JoinExpr   *joinexpr;
+	ListCell   *lc;
+	bool		src_only_tuples;
+	bool		tgt_only_tuples;
 	JoinType	jointype;
 	int			joinrti;
 	List	   *vars;
@@ -164,12 +167,32 @@ transform_MERGE_to_join(Query *parse)
 	vars = NIL;
 
 	/*
-	 * When any WHEN NOT MATCHED THEN INSERT clauses exist, we need to use an
-	 * outer join so that we process all unmatched tuples from the source
-	 * relation.  If none exist, we can use an inner join.
+	 * Work out what kind of join is required.  If there any WHEN NOT MATCHED
+	 * BY SOURCE/TARGET clauses, an outer join is required so that we process
+	 * all unmatched tuples from the source and/or target relations.
+	 * Otherwise, we can use an inner join.
 	 */
-	if (parse->mergeUseOuterJoin)
+	src_only_tuples = false;
+	tgt_only_tuples = false;
+	foreach(lc, parse->mergeActionList)
+	{
+		MergeAction *action = lfirst_node(MergeAction, lc);
+
+		if (action->commandType != CMD_NOTHING)
+		{
+			if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+				tgt_only_tuples = true;
+			if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_TARGET)
+				src_only_tuples = true;
+		}
+	}
+
+	if (src_only_tuples && tgt_only_tuples)
+		jointype = JOIN_FULL;
+	else if (src_only_tuples)
 		jointype = JOIN_RIGHT;
+	else if (tgt_only_tuples)
+		jointype = JOIN_LEFT;
 	else
 		jointype = JOIN_INNER;
 
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index efe88cc..e1ebc8d
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -273,6 +273,7 @@ static Node *makeRecursiveViewSelect(cha
 	struct SelectLimit *selectlimit;
 	SetQuantifier setquantifier;
 	struct GroupClause *groupclause;
+	MergeMatchKind mergematch;
 	MergeWhenClause *mergewhen;
 	struct KeyActions *keyactions;
 	struct KeyAction *keyaction;
@@ -512,6 +513,7 @@ static Node *makeRecursiveViewSelect(cha
 %type <onconflict> opt_on_conflict
 %type <mergewhen>	merge_insert merge_update merge_delete
 
+%type <mergematch> merge_when_tgt_matched merge_when_tgt_not_matched
 %type <node>	merge_when_clause opt_merge_when_condition
 %type <list>	merge_when_list
 
@@ -740,11 +742,11 @@ static Node *makeRecursiveViewSelect(cha
 
 	SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
-	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
+	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SOURCE SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRIP_P
 	SUBSCRIPTION SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
 
-	TABLE TABLES TABLESAMPLE TABLESPACE TEMP TEMPLATE TEMPORARY TEXT_P THEN
+	TABLE TABLES TABLESAMPLE TABLESPACE TARGET TEMP TEMPLATE TEMPORARY TEXT_P THEN
 	TIES TIME TIMESTAMP TO TRAILING TRANSACTION TRANSFORM
 	TREAT TRIGGER TRIM TRUE_P
 	TRUNCATE TRUSTED TYPE_P TYPES_P
@@ -12260,49 +12262,59 @@ merge_when_list:
 		;
 
 merge_when_clause:
-			WHEN MATCHED opt_merge_when_condition THEN merge_update
+			merge_when_tgt_matched opt_merge_when_condition THEN merge_update
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN merge_delete
+			| merge_when_tgt_matched opt_merge_when_condition THEN merge_delete
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN merge_insert
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN merge_insert
 				{
-					$6->matched = false;
-					$6->condition = $4;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $6;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = true;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $3;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = false;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $4;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
 		;
 
+merge_when_tgt_matched:
+			WHEN MATCHED					{ $$ = MERGE_WHEN_MATCHED; }
+			| WHEN NOT MATCHED BY SOURCE	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_SOURCE; }
+		;
+
+merge_when_tgt_not_matched:
+			WHEN NOT MATCHED				{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+			| WHEN NOT MATCHED BY TARGET	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+		;
+
 opt_merge_when_condition:
 			AND a_expr				{ $$ = $2; }
 			|						{ $$ = NULL; }
@@ -16968,6 +16980,7 @@ unreserved_keyword:
 			| SIMPLE
 			| SKIP
 			| SNAPSHOT
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -16986,6 +16999,7 @@ unreserved_keyword:
 			| SYSTEM_P
 			| TABLES
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
@@ -17563,6 +17577,7 @@ bare_label_keyword:
 			| SMALLINT
 			| SNAPSHOT
 			| SOME
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -17586,6 +17601,7 @@ bare_label_keyword:
 			| TABLES
 			| TABLESAMPLE
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
diff --git a/src/backend/parser/parse_merge.c b/src/backend/parser/parse_merge.c
new file mode 100644
index d886637..fca2bd9
--- a/src/backend/parser/parse_merge.c
+++ b/src/backend/parser/parse_merge.c
@@ -43,9 +43,9 @@ static void setNamespaceVisibilityForRTE
  * Make appropriate changes to the namespace visibility while transforming
  * individual action's quals and targetlist expressions. In particular, for
  * INSERT actions we must only see the source relation (since INSERT action is
- * invoked for NOT MATCHED tuples and hence there is no target tuple to deal
- * with). On the other hand, UPDATE and DELETE actions can see both source and
- * target relations.
+ * invoked for NOT MATCHED [BY TARGET] tuples and hence there is no target
+ * tuple to deal with). On the other hand, UPDATE and DELETE actions can see
+ * both source and target relations, unless invoked for NOT MATCH BY SOURCE.
  *
  * Also, since the internal join node can hide the source and target
  * relations, we must explicitly make the respective relation as visible so
@@ -61,7 +61,7 @@ setNamespaceForMergeWhen(ParseState *pst
 	targetRelRTE = rt_fetch(targetRTI, pstate->p_rtable);
 	sourceRelRTE = rt_fetch(sourceRTI, pstate->p_rtable);
 
-	if (mergeWhenClause->matched)
+	if (mergeWhenClause->matchKind == MERGE_WHEN_MATCHED)
 	{
 		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
 			   mergeWhenClause->commandType == CMD_DELETE ||
@@ -73,11 +73,25 @@ setNamespaceForMergeWhen(ParseState *pst
 		setNamespaceVisibilityForRTE(pstate->p_namespace,
 									 sourceRelRTE, true, true);
 	}
-	else
+	else if (mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
 	{
 		/*
-		 * NOT MATCHED actions can't see target relation, but they can see
-		 * source relation.
+		 * NOT MATCHED BY SOURCE actions can see the target relation, but they
+		 * can't see the source relation.
+		 */
+		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
+			   mergeWhenClause->commandType == CMD_DELETE ||
+			   mergeWhenClause->commandType == CMD_NOTHING);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 targetRelRTE, true, true);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 sourceRelRTE, false, false);
+	}
+	else	/* mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_TARGET */
+	{
+		/*
+		 * NOT MATCHED [BY TARGET] actions can't see target relation, but they
+		 * can see source relation.
 		 */
 		Assert(mergeWhenClause->commandType == CMD_INSERT ||
 			   mergeWhenClause->commandType == CMD_NOTHING);
@@ -98,7 +112,8 @@ transformMergeStmt(ParseState *pstate, M
 	Query	   *qry = makeNode(Query);
 	ListCell   *l;
 	AclMode		targetPerms = ACL_NO_RIGHTS;
-	bool		is_terminal[2];
+	bool		is_terminal[3];
+	bool		tgt_only_tuples;
 	Index		sourceRTI;
 	List	   *mergeActionList;
 	Node	   *joinExpr;
@@ -125,12 +140,13 @@ transformMergeStmt(ParseState *pstate, M
 	/*
 	 * Check WHEN clauses for permissions and sanity
 	 */
-	is_terminal[0] = false;
-	is_terminal[1] = false;
+	is_terminal[MERGE_WHEN_MATCHED] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
+	tgt_only_tuples = false;
 	foreach(l, stmt->mergeWhenClauses)
 	{
 		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
-		int			when_type = (mergeWhenClause->matched ? 0 : 1);
 
 		/*
 		 * Collect action types so we can check target permissions
@@ -155,12 +171,22 @@ transformMergeStmt(ParseState *pstate, M
 		/*
 		 * Check for unreachable WHEN clauses
 		 */
-		if (is_terminal[when_type])
+		if (is_terminal[mergeWhenClause->matchKind])
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
 					 errmsg("unreachable WHEN clause specified after unconditional WHEN clause")));
 		if (mergeWhenClause->condition == NULL)
-			is_terminal[when_type] = true;
+			is_terminal[mergeWhenClause->matchKind] = true;
+
+		/*
+		 * Test if we have a WHEN NOT MATCHED BY SOURCE action that processes
+		 * unmatched tuples from the target relation.  If so, additional WHEN
+		 * conditions are added below to differentiate the various match
+		 * kinds.
+		 */
+		if (mergeWhenClause->commandType != CMD_NOTHING &&
+			mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+			tgt_only_tuples = true;
 	}
 
 	/*
@@ -255,11 +281,7 @@ transformMergeStmt(ParseState *pstate, M
 
 		action = makeNode(MergeAction);
 		action->commandType = mergeWhenClause->commandType;
-		action->matched = mergeWhenClause->matched;
-
-		/* Use an outer join if any INSERT actions exist in the command. */
-		if (action->commandType == CMD_INSERT)
-			qry->mergeUseOuterJoin = true;
+		action->matchKind = mergeWhenClause->matchKind;
 
 		/*
 		 * Set namespace for the specific action. This must be done before
@@ -280,6 +302,51 @@ transformMergeStmt(ParseState *pstate, M
 											EXPR_KIND_MERGE_WHEN, "WHEN");
 
 		/*
+		 * If there any WHEN NOT MATCHED BY SOURCE actions that require
+		 * unmatched tuples from the target relation to be processed, add
+		 * additional WHEN conditions to every action to check that tuples
+		 * from the source match or do not match, as necessary.
+		 *
+		 * This distinguishes NOT MATCHED BY SOURCE actions (identified by a
+		 * "source IS NOT DISTINCT FROM NULL" clause) from MATCHED actions
+		 * (identified by a "source IS DISTINCT FROM NULL" clause).
+		 *
+		 * Additionally, a "source IS DISTINCT FROM NULL" clause is required
+		 * for NOT MATCHED [BY TARGET] actions in case the executor attempts
+		 * to invoke such an action for a concurrently deleted target row that
+		 * ends up matching neither source nor target.
+		 */
+		if (tgt_only_tuples)
+		{
+			bool		src_null;
+			NullTest   *ntest;
+
+			/* Make a "source IS [NOT] DISTINCT FROM NULL" clause */
+			src_null = action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE;
+
+			ntest = makeNode(NullTest);
+
+			ntest->arg = (Expr *) makeVar(sourceRTI,
+										  InvalidAttrNumber,
+										  RECORDOID,
+										  -1,
+										  InvalidOid,
+										  0);
+			ntest->nulltesttype = src_null ? IS_NULL : IS_NOT_NULL;
+			ntest->argisrow = false;
+			ntest->location = -1;
+
+			/* Combine it with the action's WHEN condition */
+			if (action->qual == NULL)
+				action->qual = (Node *) ntest;
+			else
+				action->qual =
+					(Node *) makeBoolExpr(AND_EXPR,
+										  list_make2(ntest, action->qual),
+										  -1);
+		}
+
+		/*
 		 * Transform target lists for each INSERT and UPDATE action stmt
 		 */
 		switch (action->commandType)
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
new file mode 100644
index 42e87b9..941c64b
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -4237,17 +4237,35 @@ psql_completion(const char *text, int st
 			 TailMatches("USING", MatchAny, MatchAny, "ON", MatchAny, MatchAny, MatchAny, "WHEN"))
 		COMPLETE_WITH("MATCHED", "NOT MATCHED");
 
-	/* Complete ... WHEN [NOT] MATCHED with THEN/AND */
+	/*
+	 * Complete ... WHEN MATCHED and WHEN NOT MATCHED BY SOURCE|TARGET with
+	 * THEN/AND
+	 */
 	else if (TailMatches("WHEN", "MATCHED") ||
-			 TailMatches("WHEN", "NOT", "MATCHED"))
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE|TARGET"))
 		COMPLETE_WITH("THEN", "AND");
 
-	/* Complete ... WHEN MATCHED THEN with UPDATE SET/DELETE/DO NOTHING */
-	else if (TailMatches("WHEN", "MATCHED", "THEN"))
+	/* Complete ... WHEN NOT MATCHED with BY/THEN/AND */
+	else if (TailMatches("WHEN", "NOT", "MATCHED"))
+		COMPLETE_WITH("BY", "THEN", "AND");
+
+	/* Complete ... WHEN NOT MATCHED BY with SOURCE/TARGET */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "BY"))
+		COMPLETE_WITH("SOURCE", "TARGET");
+
+	/*
+	 * Complete ... WHEN MATCHED THEN and WHEN NOT MATCHED BY SOURCE THEN with
+	 * UPDATE SET/DELETE/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE", "THEN"))
 		COMPLETE_WITH("UPDATE SET", "DELETE", "DO NOTHING");
 
-	/* Complete ... WHEN NOT MATCHED THEN with INSERT/DO NOTHING */
-	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN"))
+	/*
+	 * Complete ... WHEN NOT MATCHED [BY TARGET] THEN with INSERT/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "TARGET", "THEN"))
 		COMPLETE_WITH("INSERT", "DO NOTHING");
 
 /* NOTIFY --- can be inside EXPLAIN, RULE, etc */
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
new file mode 100644
index 028588f..e4ce377
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -183,8 +183,6 @@ typedef struct Query
 								 * also USING clause for MERGE */
 
 	List	   *mergeActionList;	/* list of actions for MERGE (only) */
-	/* whether to use outer join */
-	bool		mergeUseOuterJoin pg_node_attr(query_jumble_ignore);
 
 	List	   *targetList;		/* target list (of TargetEntry) */
 
@@ -1662,6 +1660,14 @@ typedef struct CommonTableExpr
 	 ((Query *) (cte)->ctequery)->targetList : \
 	 ((Query *) (cte)->ctequery)->returningList)
 
+/* MATCHED/NOT MATCHED specification for WHEN clauses in a MERGE statement */
+typedef enum MergeMatchKind
+{
+	MERGE_WHEN_MATCHED,
+	MERGE_WHEN_NOT_MATCHED_BY_SOURCE,
+	MERGE_WHEN_NOT_MATCHED_BY_TARGET
+} MergeMatchKind;
+
 /*
  * MergeWhenClause -
  *		raw parser representation of a WHEN clause in a MERGE statement
@@ -1671,7 +1677,7 @@ typedef struct CommonTableExpr
 typedef struct MergeWhenClause
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *condition;		/* WHEN conditions (raw parser) */
@@ -1687,7 +1693,7 @@ typedef struct MergeWhenClause
 typedef struct MergeAction
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	/* OVERRIDING clause */
 	OverridingKind override pg_node_attr(query_jumble_ignore);
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
new file mode 100644
index 753e9ee..b213b99
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -392,6 +392,7 @@ PG_KEYWORD("skip", SKIP, UNRESERVED_KEYW
 PG_KEYWORD("smallint", SMALLINT, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("snapshot", SNAPSHOT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("some", SOME, RESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("source", SOURCE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("sql", SQL_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("stable", STABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("standalone", STANDALONE_P, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -415,6 +416,7 @@ PG_KEYWORD("table", TABLE, RESERVED_KEYW
 PG_KEYWORD("tables", TABLES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablesample", TABLESAMPLE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablespace", TABLESPACE, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("target", TARGET, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temp", TEMP, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("template", TEMPLATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temporary", TEMPORARY, UNRESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/test/regress/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index 1ddc68b..8ad2a62
--- a/src/test/regress/expected/merge.out
+++ b/src/test/regress/expected/merge.out
@@ -71,6 +71,15 @@ WHEN MATCHED THEN
 ERROR:  syntax error at or near "INSERT"
 LINE 5:  INSERT DEFAULT VALUES;
          ^
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
+ERROR:  syntax error at or near "INSERT"
+LINE 5:  INSERT DEFAULT VALUES;
+         ^
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -107,6 +116,15 @@ WHEN NOT MATCHED THEN
 ERROR:  syntax error at or near "UPDATE"
 LINE 5:  UPDATE SET balance = 0;
          ^
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
+ERROR:  syntax error at or near "UPDATE"
+LINE 5:  UPDATE SET balance = 0;
+         ^
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -271,6 +289,22 @@ SELECT * FROM target ORDER BY tid;
 (4 rows)
 
 ROLLBACK;
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   4 |      40
+(1 row)
+
+ROLLBACK;
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -738,6 +772,19 @@ SELECT * FROM wq_target;
    1 |      -1
 (1 row)
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+ERROR:  invalid reference to FROM-clause entry for table "s"
+LINE 3: WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+                                       ^
+DETAIL:  There is an entry for table "s", but it cannot be referenced from this part of the query.
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
  balance | sid 
@@ -923,6 +970,45 @@ SELECT * FROM target ORDER BY tid;
 (3 rows)
 
 ROLLBACK;
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE DELETE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  BEFORE INSERT ROW trigger row: (4,40)
+NOTICE:  BEFORE DELETE ROW trigger row: (2,20)
+NOTICE:  BEFORE UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  AFTER INSERT ROW trigger row: (4,40)
+NOTICE:  AFTER DELETE ROW trigger row: (2,20)
+NOTICE:  AFTER UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER DELETE STATEMENT trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |       0
+   3 |      10
+   4 |      40
+(3 rows)
+
+ROLLBACK;
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -1451,6 +1537,50 @@ WHEN NOT MATCHED AND s.a < 20 THEN
                ->  Seq Scan on ex_mtarget t (actual rows=49 loops=1)
 (12 rows)
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=54
+   ->  Merge Left Join (actual rows=54 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=100
+   ->  Merge Full Join (actual rows=100 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index 29a3548..76bb9fd
--- a/src/test/regress/sql/merge.sql
+++ b/src/test/regress/sql/merge.sql
@@ -51,6 +51,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN MATCHED THEN
 	INSERT DEFAULT VALUES;
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -75,6 +81,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN NOT MATCHED THEN
 	UPDATE SET balance = 0;
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -213,6 +225,18 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -497,6 +521,17 @@ WHEN NOT MATCHED AND s.balance = 100 THE
 	INSERT (tid) VALUES (s.sid);
 SELECT * FROM wq_target;
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
+
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
 MERGE INTO wq_target t
@@ -624,6 +659,25 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -929,6 +983,20 @@ WHEN MATCHED AND t.a >= 30 AND t.a <= 40
 WHEN NOT MATCHED AND s.a < 20 THEN
 	INSERT VALUES (a, b)');
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
new file mode 100644
index f8f83d4..6ef0c2b
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -396,8 +396,8 @@
     originally matched appears later in the list of actions.
     On the other hand, if the row is concurrently updated or deleted so
     that the join condition fails, then <command>MERGE</command> will
-    evaluate the condition's <literal>NOT MATCHED</literal> actions next,
-    and execute the first one that succeeds.
+    evaluate the condition's <literal>NOT MATCHED [BY TARGET]</literal>
+    actions next, and execute the first one that succeeds.
     If <command>MERGE</command> attempts an <command>INSERT</command>
     and a unique index is present and a duplicate row is concurrently
     inserted, then a uniqueness violation error is raised;
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
new file mode 100644
index 0995fe0..8ef121a
--- a/doc/src/sgml/ref/merge.sgml
+++ b/doc/src/sgml/ref/merge.sgml
@@ -33,7 +33,8 @@ USING <replaceable class="parameter">dat
 <phrase>and <replaceable class="parameter">when_clause</replaceable> is:</phrase>
 
 { WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
-  WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
+  WHEN NOT MATCHED BY SOURCE [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
+  WHEN NOT MATCHED [BY TARGET] [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
 
 <phrase>and <replaceable class="parameter">merge_insert</replaceable> is:</phrase>
 
@@ -70,7 +71,9 @@ DELETE
    from <replaceable class="parameter">data_source</replaceable> to
    <replaceable class="parameter">target_table_name</replaceable>
    producing zero or more candidate change rows.  For each candidate change
-   row, the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal>
+   row, the status of <literal>MATCHED</literal>,
+   <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>
    is set just once, after which <literal>WHEN</literal> clauses are evaluated
    in the order specified.  For each candidate change row, the first clause to
    evaluate as true is executed.  No more than one <literal>WHEN</literal>
@@ -226,16 +229,37 @@ DELETE
       At least one <literal>WHEN</literal> clause is required.
      </para>
      <para>
+      The <literal>WHEN</literal> clause may specify <literal>WHEN MATCHED</literal>,
+      <literal>WHEN NOT MATCHED BY SOURCE</literal>, or
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>.
+      Note that the <acronym>SQL</acronym> standard only defines
+      <literal>WHEN MATCHED</literal> and <literal>WHEN NOT MATCHED</literal>
+      (which is defined to mean no matching target row).
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> is an extension to the
+      <acronym>SQL</acronym> standard, as is the option to append
+      <literal>BY TARGET</literal> to <literal>WHEN NOT MATCHED</literal>, to
+      make its meaning more explicit.
+     </para>
+     <para>
       If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
-      and the candidate change row matches a row in the
+      and the candidate change row matches a row in the source to a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
      </para>
      <para>
-      Conversely, if the <literal>WHEN</literal> clause specifies
-      <literal>WHEN NOT MATCHED</literal>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> and the candidate change
+      row represents a row in the
+      <replaceable class="parameter">target_table_name</replaceable> that does
+      not match a source row, the <literal>WHEN</literal> clause is executed
+      if the <replaceable class="parameter">condition</replaceable> is
+      absent or it evaluates to <literal>true</literal>.
+     </para>
+     <para>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>
       and the candidate change row does not match a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
@@ -257,7 +281,10 @@ DELETE
      <para>
       A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
       in both the source and the target relations. A condition on a
-      <literal>WHEN NOT MATCHED</literal> clause can only refer to columns from
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> clause can only refer to
+      columns from the target relation, since by definition there is no matching
+      source row. A condition on a <literal>WHEN NOT MATCHED [BY TARGET]</literal>
+      clause can only refer to columns from
       the source relation, since by definition there is no matching target row.
       Only the system attributes from the target table are accessible.
      </para>
@@ -382,8 +409,10 @@ DELETE
       <literal>WHEN MATCHED</literal> clause, the expression can use values
       from the original row in the target table, and values from the
       <literal>data_source</literal> row.
-      If used in a <literal>WHEN NOT MATCHED</literal> clause, the
-      expression can use values from the <literal>data_source</literal>.
+      If used in a <literal>WHEN NOT MATCHED BY SOURCE</literal> clause, the
+      expression can only use values from the original row in the target table.
+      If used in a <literal>WHEN NOT MATCHED [BY TARGET]</literal> clause, the
+      expression can only use values from the <literal>data_source</literal>.
      </para>
     </listitem>
    </varlistentry>
@@ -452,8 +481,9 @@ MERGE <replaceable class="parameter">tot
        <orderedlist>
         <listitem>
          <para>
-          Evaluate whether each row is <literal>MATCHED</literal> or
-          <literal>NOT MATCHED</literal>.
+          Evaluate whether each row is <literal>MATCHED</literal>,
+          <literal>NOT MATCHED BY SOURCE</literal>, or
+          <literal>NOT MATCHED [BY TARGET]</literal>.
          </para>
         </listitem>
         <listitem>
@@ -528,7 +558,8 @@ MERGE <replaceable class="parameter">tot
   <para>
    If a <literal>WHEN</literal> clause omits an <literal>AND</literal>
    sub-clause, it becomes the final reachable clause of that
-   kind (<literal>MATCHED</literal> or <literal>NOT MATCHED</literal>).
+   kind (<literal>MATCHED</literal>, <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>).
    If a later <literal>WHEN</literal> clause of that kind
    is specified it would be provably unreachable and an error is raised.
    If no final reachable clause is specified of either kind, it is
@@ -619,6 +650,23 @@ WHEN MATCHED THEN
    temporary table recently loaded into the database.
   </para>
 
+  <para>
+   Update <literal>wine</literal> based on a replacement wine list, inserting
+   rows for any new stock, updating modified stock entries, and deleting any
+   wines not present in the new list.
+<programlisting>
+MERGE INTO wines w
+USING new_wine_list s
+ON s.winename = w.winename
+WHEN NOT MATCHED BY TARGET THEN
+  INSERT VALUES(s.winename, s.stock)
+WHEN MATCHED AND w.stock != s.stock THEN
+  UPDATE SET stock = s.stock
+WHEN NOT MATCHED BY SOURCE THEN
+  DELETE;
+</programlisting>
+  </para>
+
  </refsect1>
 
  <refsect1>
@@ -627,7 +675,10 @@ WHEN MATCHED THEN
     This command conforms to the <acronym>SQL</acronym> standard.
   </para>
    <para>
-    The WITH clause and <literal>DO NOTHING</literal> action are extensions to
+    The WITH clause, <literal>BY SOURCE</literal> and
+    <literal>BY TARGET</literal> qualifiers to
+    <literal>WHEN NOT MATCHED</literal>, and
+    <literal>DO NOTHING</literal> action are extensions to
     the <acronym>SQL</acronym> standard.
   </para>
  </refsect1>
diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
new file mode 100644
index eb8a87f..a1add5a
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -902,8 +902,16 @@ ExecInitPartitionInfo(ModifyTableState *
 			action_state = makeNode(MergeActionState);
 			action_state->mas_action = action;
 
-			/* And put the action in the appropriate list */
-			if (action->matched)
+			/*
+			 * Put the action in the appropriate list.
+			 *
+			 * Note that the executor treats WHEN NOT MATCHED BY SOURCE
+			 * actions in exactly the same way as WHEN MATCHED actions, since
+			 * they both match the target (see ExecMerge).  Thus both types go
+			 * in the "matched" list.  Only WHEN NOT MATCHED BY TARGET actions
+			 * go in the "not matched" list.
+			 */
+			if (action->matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET)
 				list = &leaf_part_rri->ri_matchedMergeAction;
 			else
 				list = &leaf_part_rri->ri_notMatchedMergeAction;
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
new file mode 100644
index 2a5fec8..314dbaf
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -24,13 +24,15 @@
  *		values plus row-locating info for UPDATE and MERGE cases, or just the
  *		row-locating info for DELETE cases.
  *
- *		MERGE runs a join between the source relation and the target
- *		table; if any WHEN NOT MATCHED clauses are present, then the
- *		join is an outer join.  In this case, any unmatched tuples will
- *		have NULL row-locating info, and only INSERT can be run. But for
- *		matched tuples, then row-locating info is used to determine the
- *		tuple to UPDATE or DELETE. When all clauses are WHEN MATCHED,
- *		then an inner join is used, so all tuples contain row-locating info.
+ *		MERGE runs a join between the source relation and the target table.
+ *		If any WHEN NOT MATCHED [BY TARGET] clauses are present, then the join
+ *		is an outer join that might output tuples without a matching target
+ *		tuple.  In this case, any unmatched target tuples will have NULL
+ *		row-locating info, and only INSERT can be run.  But for matched
+ *		target tuples, the row-locating info is used to determine the tuple
+ *		to UPDATE or DELETE.  When all clauses are WHEN MATCHED or WHEN NOT
+ *		MATCHED BY SOURCE, all tuples produced by the join will include a
+ *		matching target tuple, so all tuples contain row-locating info.
  *
  *		If the query specifies RETURNING, then the ModifyTable returns a
  *		RETURNING tuple after completing each row insert, update, or delete.
@@ -2715,6 +2717,17 @@ ExecMerge(ModifyTableContext *context, R
 	bool		matched;
 
 	/*-----
+	 * Note that as far as the executor is concerned, WHEN NOT MATCHED BY
+	 * SOURCE actions are treated exactly the same as WHEN MATCHED actions,
+	 * since both match target tuples.  They are distinguished from one
+	 * another by a qual that tests if the source tuple is NULL, but the
+	 * executor knows nothing about the contents of the merge action quals.
+	 * Thus WHEN MATCHED and WHEN NOT MATCHED BY SOURCE actions are stored
+	 * together in the same "matched" list.  Thus, in the dicussion that
+	 * follows "MATCHED" means "matched by target", and should be taken to
+	 * include both WHEN MATCHED and WHEN NOT MATCHED BY SOURCE, while "NOT
+	 * MATCHED" means NOT MATCHED BY TARGET.
+	 *
 	 * If we are dealing with a WHEN MATCHED case (tupleid is valid), we
 	 * execute the first action for which the additional WHEN MATCHED AND
 	 * quals pass.  If an action without quals is found, that action is
@@ -3044,9 +3057,13 @@ lmerge_matched:
 							 * is executed.
 							 *
 							 * Update tupleid to that of the new tuple, for
-							 * the refetch we do at the top.
+							 * the refetch we do at the top, and install the
+							 * updated plan slot in ecxt_innertuple in case
+							 * the source tuple is now NULL (a change from
+							 * MATCHED to NOT MATCHED BY SOURCE).
 							 */
 							ItemPointerCopy(&context->tmfd.ctid, tupleid);
+							econtext->ecxt_innertuple = epqslot;
 							goto lmerge_matched;
 
 						case TM_Deleted:
@@ -3251,8 +3268,14 @@ ExecInitMerge(ModifyTableState *mtstate,
 			 * We create two lists - one for WHEN MATCHED actions and one for
 			 * WHEN NOT MATCHED actions - and stick the MergeActionState into
 			 * the appropriate list.
+			 *
+			 * Note that the executor treats WHEN NOT MATCHED BY SOURCE
+			 * actions in exactly the same way as WHEN MATCHED actions, since
+			 * they both match the target (see ExecMerge).  Thus both types go
+			 * in the "matched" list.  Only WHEN NOT MATCHED BY TARGET actions
+			 * go in the "not matched" list.
 			 */
-			if (action_state->mas_action->matched)
+			if (action->matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET)
 				list = &resultRelInfo->ri_matchedMergeAction;
 			else
 				list = &resultRelInfo->ri_notMatchedMergeAction;
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
new file mode 100644
index 73ff407..be45646
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -153,6 +153,9 @@ transform_MERGE_to_join(Query *parse)
 {
 	RangeTblEntry *joinrte;
 	JoinExpr   *joinexpr;
+	ListCell   *lc;
+	bool		src_only_tuples;
+	bool		tgt_only_tuples;
 	JoinType	jointype;
 	int			joinrti;
 	List	   *vars;
@@ -164,12 +167,32 @@ transform_MERGE_to_join(Query *parse)
 	vars = NIL;
 
 	/*
-	 * When any WHEN NOT MATCHED THEN INSERT clauses exist, we need to use an
-	 * outer join so that we process all unmatched tuples from the source
-	 * relation.  If none exist, we can use an inner join.
+	 * Work out what kind of join is required.  If there any WHEN NOT MATCHED
+	 * BY SOURCE/TARGET actions, an outer join is required so that we process
+	 * all unmatched tuples from the source and/or target relations.
+	 * Otherwise, we can use an inner join.
 	 */
-	if (parse->mergeUseOuterJoin)
+	src_only_tuples = false;
+	tgt_only_tuples = false;
+	foreach(lc, parse->mergeActionList)
+	{
+		MergeAction *action = lfirst_node(MergeAction, lc);
+
+		if (action->commandType != CMD_NOTHING)
+		{
+			if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+				tgt_only_tuples = true;
+			if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_TARGET)
+				src_only_tuples = true;
+		}
+	}
+
+	if (src_only_tuples && tgt_only_tuples)
+		jointype = JOIN_FULL;
+	else if (src_only_tuples)
 		jointype = JOIN_RIGHT;
+	else if (tgt_only_tuples)
+		jointype = JOIN_LEFT;
 	else
 		jointype = JOIN_INNER;
 
@@ -215,6 +238,51 @@ transform_MERGE_to_join(Query *parse)
 	/* Make the new join be the sole entry in the query's jointree */
 	parse->jointree->fromlist = list_make1(joinexpr);
 	parse->jointree->quals = NULL;
+
+	/*
+	 * If there any WHEN NOT MATCHED BY SOURCE actions that require unmatched
+	 * tuples from the target relation to be processed, add additional WHEN
+	 * conditions to every action to check whether tuples from the source
+	 * match or not, as necessary.
+	 *
+	 * This distinguishes WHEN NOT MATCHED BY SOURCE actions (identified by a
+	 * "source IS NOT DISTINCT FROM NULL" clause) from WHEN MATCHED actions
+	 * (identified by a "source IS DISTINCT FROM NULL" clause).
+	 *
+	 * Additionally, a "source IS DISTINCT FROM NULL" clause is required for
+	 * WHEN NOT MATCHED [BY TARGET] actions in case the executor attempts to
+	 * invoke such an action for a concurrently deleted target row that ends
+	 * up matching neither source nor target.
+	 */
+	if (tgt_only_tuples)
+	{
+		foreach(lc, parse->mergeActionList)
+		{
+			MergeAction *action = lfirst_node(MergeAction, lc);
+			bool		src_null;
+			Var		   *var;
+			NullTest   *ntest;
+
+			/* Make a "source IS [NOT] DISTINCT FROM NULL" clause */
+			src_null = action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE;
+
+			var = makeWholeRowVar(rt_fetch(parse->mergeSourceRelation,
+										   parse->rtable),
+								  parse->mergeSourceRelation, 0, false);
+
+			/* source wholerow Var is nullable by the new join */
+			var->varnullingrels = bms_make_singleton(joinrti);
+
+			ntest = makeNode(NullTest);
+			ntest->arg = (Expr *) var;
+			ntest->nulltesttype = src_null ? IS_NULL : IS_NOT_NULL;
+			ntest->argisrow = false;
+			ntest->location = -1;
+
+			/* Combine it with the action's WHEN condition */
+			action->qual = make_and_qual((Node *) ntest, action->qual);
+		}
+	}
 }
 
 /*
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index 39ab7ea..2f152f0
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -275,6 +275,7 @@ static Node *makeRecursiveViewSelect(cha
 	struct SelectLimit *selectlimit;
 	SetQuantifier setquantifier;
 	struct GroupClause *groupclause;
+	MergeMatchKind mergematch;
 	MergeWhenClause *mergewhen;
 	struct KeyActions *keyactions;
 	struct KeyAction *keyaction;
@@ -514,6 +515,7 @@ static Node *makeRecursiveViewSelect(cha
 %type <onconflict> opt_on_conflict
 %type <mergewhen>	merge_insert merge_update merge_delete
 
+%type <mergematch> merge_when_tgt_matched merge_when_tgt_not_matched
 %type <node>	merge_when_clause opt_merge_when_condition
 %type <list>	merge_when_list
 
@@ -760,11 +762,11 @@ static Node *makeRecursiveViewSelect(cha
 	SAVEPOINT SCALAR SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT
 	SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
-	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
+	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SOURCE SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRIP_P
 	SUBSCRIPTION SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
 
-	TABLE TABLES TABLESAMPLE TABLESPACE TEMP TEMPLATE TEMPORARY TEXT_P THEN
+	TABLE TABLES TABLESAMPLE TABLESPACE TARGET TEMP TEMPLATE TEMPORARY TEXT_P THEN
 	TIES TIME TIMESTAMP TO TRAILING TRANSACTION TRANSFORM
 	TREAT TRIGGER TRIM TRUE_P
 	TRUNCATE TRUSTED TYPE_P TYPES_P
@@ -12267,50 +12269,66 @@ merge_when_list:
 			| merge_when_list merge_when_clause		{ $$ = lappend($1,$2); }
 		;
 
+/*
+ * A WHEN clause may be WHEN MATCHED, WHEN NOT MATCHED BY SOURCE, or WHEN NOT
+ * MATCHED [BY TARGET]. The first two cases match target tuples, and support
+ * UPDATE/DELETE/DO NOTHING actions. The third case does not match target
+ * tuples, and only supports INSERT/DO NOTHING actions.
+ */
 merge_when_clause:
-			WHEN MATCHED opt_merge_when_condition THEN merge_update
+			merge_when_tgt_matched opt_merge_when_condition THEN merge_update
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN merge_delete
+			| merge_when_tgt_matched opt_merge_when_condition THEN merge_delete
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN merge_insert
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN merge_insert
 				{
-					$6->matched = false;
-					$6->condition = $4;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $6;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = true;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $3;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = false;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $4;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
 		;
 
+merge_when_tgt_matched:
+			WHEN MATCHED					{ $$ = MERGE_WHEN_MATCHED; }
+			| WHEN NOT MATCHED BY SOURCE	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_SOURCE; }
+		;
+
+merge_when_tgt_not_matched:
+			WHEN NOT MATCHED				{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+			| WHEN NOT MATCHED BY TARGET	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+		;
+
 opt_merge_when_condition:
 			AND a_expr				{ $$ = $2; }
 			|						{ $$ = NULL; }
@@ -17192,6 +17210,7 @@ unreserved_keyword:
 			| SIMPLE
 			| SKIP
 			| SNAPSHOT
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -17210,6 +17229,7 @@ unreserved_keyword:
 			| SYSTEM_P
 			| TABLES
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
@@ -17800,6 +17820,7 @@ bare_label_keyword:
 			| SMALLINT
 			| SNAPSHOT
 			| SOME
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -17823,6 +17844,7 @@ bare_label_keyword:
 			| TABLES
 			| TABLESAMPLE
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
diff --git a/src/backend/parser/parse_merge.c b/src/backend/parser/parse_merge.c
new file mode 100644
index 91b1156..728b533
--- a/src/backend/parser/parse_merge.c
+++ b/src/backend/parser/parse_merge.c
@@ -43,9 +43,9 @@ static void setNamespaceVisibilityForRTE
  * Make appropriate changes to the namespace visibility while transforming
  * individual action's quals and targetlist expressions. In particular, for
  * INSERT actions we must only see the source relation (since INSERT action is
- * invoked for NOT MATCHED tuples and hence there is no target tuple to deal
- * with). On the other hand, UPDATE and DELETE actions can see both source and
- * target relations.
+ * invoked for NOT MATCHED [BY TARGET] tuples and hence there is no target
+ * tuple to deal with). On the other hand, UPDATE and DELETE actions can see
+ * both source and target relations, unless invoked for NOT MATCHED BY SOURCE.
  *
  * Also, since the internal join node can hide the source and target
  * relations, we must explicitly make the respective relation as visible so
@@ -61,7 +61,7 @@ setNamespaceForMergeWhen(ParseState *pst
 	targetRelRTE = rt_fetch(targetRTI, pstate->p_rtable);
 	sourceRelRTE = rt_fetch(sourceRTI, pstate->p_rtable);
 
-	if (mergeWhenClause->matched)
+	if (mergeWhenClause->matchKind == MERGE_WHEN_MATCHED)
 	{
 		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
 			   mergeWhenClause->commandType == CMD_DELETE ||
@@ -73,11 +73,25 @@ setNamespaceForMergeWhen(ParseState *pst
 		setNamespaceVisibilityForRTE(pstate->p_namespace,
 									 sourceRelRTE, true, true);
 	}
-	else
+	else if (mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
 	{
 		/*
-		 * NOT MATCHED actions can't see target relation, but they can see
-		 * source relation.
+		 * NOT MATCHED BY SOURCE actions can see the target relation, but they
+		 * can't see the source relation.
+		 */
+		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
+			   mergeWhenClause->commandType == CMD_DELETE ||
+			   mergeWhenClause->commandType == CMD_NOTHING);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 targetRelRTE, true, true);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 sourceRelRTE, false, false);
+	}
+	else						/* MERGE_WHEN_NOT_MATCHED_BY_TARGET */
+	{
+		/*
+		 * NOT MATCHED [BY TARGET] actions can't see target relation, but they
+		 * can see source relation.
 		 */
 		Assert(mergeWhenClause->commandType == CMD_INSERT ||
 			   mergeWhenClause->commandType == CMD_NOTHING);
@@ -98,8 +112,7 @@ transformMergeStmt(ParseState *pstate, M
 	Query	   *qry = makeNode(Query);
 	ListCell   *l;
 	AclMode		targetPerms = ACL_NO_RIGHTS;
-	bool		is_terminal[2];
-	Index		sourceRTI;
+	bool		is_terminal[3];
 	List	   *mergeActionList;
 	Node	   *joinExpr;
 	ParseNamespaceItem *nsitem;
@@ -125,12 +138,12 @@ transformMergeStmt(ParseState *pstate, M
 	/*
 	 * Check WHEN clauses for permissions and sanity
 	 */
-	is_terminal[0] = false;
-	is_terminal[1] = false;
+	is_terminal[MERGE_WHEN_MATCHED] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
 	foreach(l, stmt->mergeWhenClauses)
 	{
 		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
-		int			when_type = (mergeWhenClause->matched ? 0 : 1);
 
 		/*
 		 * Collect action types so we can check target permissions
@@ -155,12 +168,12 @@ transformMergeStmt(ParseState *pstate, M
 		/*
 		 * Check for unreachable WHEN clauses
 		 */
-		if (is_terminal[when_type])
+		if (is_terminal[mergeWhenClause->matchKind])
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
 					 errmsg("unreachable WHEN clause specified after unconditional WHEN clause")));
 		if (mergeWhenClause->condition == NULL)
-			is_terminal[when_type] = true;
+			is_terminal[mergeWhenClause->matchKind] = true;
 	}
 
 	/*
@@ -193,8 +206,8 @@ transformMergeStmt(ParseState *pstate, M
 	/* Now transform the source relation to produce the source RTE. */
 	transformFromClause(pstate,
 						list_make1(stmt->sourceRelation));
-	sourceRTI = list_length(pstate->p_rtable);
-	nsitem = GetNSItemByRangeTablePosn(pstate, sourceRTI, 0);
+	qry->mergeSourceRelation = list_length(pstate->p_rtable);
+	nsitem = GetNSItemByRangeTablePosn(pstate, qry->mergeSourceRelation, 0);
 
 	/*
 	 * Check that the target table doesn't conflict with the source table.
@@ -255,11 +268,7 @@ transformMergeStmt(ParseState *pstate, M
 
 		action = makeNode(MergeAction);
 		action->commandType = mergeWhenClause->commandType;
-		action->matched = mergeWhenClause->matched;
-
-		/* Use an outer join if any INSERT actions exist in the command. */
-		if (action->commandType == CMD_INSERT)
-			qry->mergeUseOuterJoin = true;
+		action->matchKind = mergeWhenClause->matchKind;
 
 		/*
 		 * Set namespace for the specific action. This must be done before
@@ -267,7 +276,7 @@ transformMergeStmt(ParseState *pstate, M
 		 */
 		setNamespaceForMergeWhen(pstate, mergeWhenClause,
 								 qry->resultRelation,
-								 sourceRTI);
+								 qry->mergeSourceRelation);
 
 		/*
 		 * Transform the WHEN condition.
diff --git a/src/backend/rewrite/rewriteManip.c b/src/backend/rewrite/rewriteManip.c
new file mode 100644
index 32bd2f1..fcf78c4
--- a/src/backend/rewrite/rewriteManip.c
+++ b/src/backend/rewrite/rewriteManip.c
@@ -496,9 +496,10 @@ OffsetVarNodes(Node *node, int offset, i
 		/*
 		 * If we are starting at a Query, and sublevels_up is zero, then we
 		 * must also fix rangetable indexes in the Query itself --- namely
-		 * resultRelation, exclRelIndex and rowMarks entries.  sublevels_up
-		 * cannot be zero when recursing into a subquery, so there's no need
-		 * to have the same logic inside OffsetVarNodes_walker.
+		 * resultRelation, mergeSourceRelation, exclRelIndex and rowMarks
+		 * entries.  sublevels_up cannot be zero when recursing into a
+		 * subquery, so there's no need to have the same logic inside
+		 * OffsetVarNodes_walker.
 		 */
 		if (sublevels_up == 0)
 		{
@@ -507,6 +508,9 @@ OffsetVarNodes(Node *node, int offset, i
 			if (qry->resultRelation)
 				qry->resultRelation += offset;
 
+			if (qry->mergeSourceRelation)
+				qry->mergeSourceRelation += offset;
+
 			if (qry->onConflict && qry->onConflict->exclRelIndex)
 				qry->onConflict->exclRelIndex += offset;
 
@@ -687,9 +691,10 @@ ChangeVarNodes(Node *node, int rt_index,
 		/*
 		 * If we are starting at a Query, and sublevels_up is zero, then we
 		 * must also fix rangetable indexes in the Query itself --- namely
-		 * resultRelation and rowMarks entries.  sublevels_up cannot be zero
-		 * when recursing into a subquery, so there's no need to have the same
-		 * logic inside ChangeVarNodes_walker.
+		 * resultRelation, mergeSourceRelation, exclRelIndex and rowMarks
+		 * entries.  sublevels_up cannot be zero when recursing into a
+		 * subquery, so there's no need to have the same logic inside
+		 * ChangeVarNodes_walker.
 		 */
 		if (sublevels_up == 0)
 		{
@@ -698,6 +703,9 @@ ChangeVarNodes(Node *node, int rt_index,
 			if (qry->resultRelation == rt_index)
 				qry->resultRelation = new_index;
 
+			if (qry->mergeSourceRelation == rt_index)
+				qry->mergeSourceRelation = new_index;
+
 			/* this is unlikely to ever be used, but ... */
 			if (qry->onConflict && qry->onConflict->exclRelIndex == rt_index)
 				qry->onConflict->exclRelIndex = new_index;
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
new file mode 100644
index d3a973d..1d78714
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -7077,6 +7077,7 @@ get_merge_query_def(Query *query, depars
 	StringInfo	buf = context->buf;
 	RangeTblEntry *rte;
 	ListCell   *lc;
+	bool		haveNotMatchedBySource;
 
 	/* Insert the WITH clause if given */
 	get_with_clause(query, context);
@@ -7104,6 +7105,25 @@ get_merge_query_def(Query *query, depars
 						 -PRETTYINDENT_STD, PRETTYINDENT_STD, 2);
 	get_rule_expr(query->jointree->quals, context, false);
 
+	/*
+	 * Test for any NOT MATCHED BY SOURCE actions.  If there are none, then
+	 * any NOT MATCHED BY TARGET actions are output as "WHEN NOT MATCHED", per
+	 * SQL standard.  Otherwise, we have a non-SQL-standard query, so output
+	 * "BY SOURCE" / "BY TARGET" qualifiers for all NOT MATCHED actions, to be
+	 * more explicit.
+	 */
+	haveNotMatchedBySource = false;
+	foreach(lc, query->mergeActionList)
+	{
+		MergeAction *action = lfirst_node(MergeAction, lc);
+
+		if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+		{
+			haveNotMatchedBySource = true;
+			break;
+		}
+	}
+
 	/* Print each merge action */
 	foreach(lc, query->mergeActionList)
 	{
@@ -7111,7 +7131,24 @@ get_merge_query_def(Query *query, depars
 
 		appendContextKeyword(context, " WHEN ",
 							 -PRETTYINDENT_STD, PRETTYINDENT_STD, 2);
-		appendStringInfo(buf, "%sMATCHED", action->matched ? "" : "NOT ");
+		switch (action->matchKind)
+		{
+			case MERGE_WHEN_MATCHED:
+				appendStringInfo(buf, "MATCHED");
+				break;
+			case MERGE_WHEN_NOT_MATCHED_BY_SOURCE:
+				appendStringInfo(buf, "NOT MATCHED BY SOURCE");
+				break;
+			case MERGE_WHEN_NOT_MATCHED_BY_TARGET:
+				if (haveNotMatchedBySource)
+					appendStringInfo(buf, "NOT MATCHED BY TARGET");
+				else
+					appendStringInfo(buf, "NOT MATCHED");
+				break;
+			default:
+				elog(ERROR, "unrecognized matchKind: %d",
+					 (int) action->matchKind);
+		}
 
 		if (action->qual)
 		{
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
new file mode 100644
index 935bb9b..6cfff24
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -4270,17 +4270,35 @@ psql_completion(const char *text, int st
 			 TailMatches("USING", MatchAny, MatchAny, "ON", MatchAny, MatchAny, MatchAny, "WHEN"))
 		COMPLETE_WITH("MATCHED", "NOT MATCHED");
 
-	/* Complete ... WHEN [NOT] MATCHED with THEN/AND */
+	/*
+	 * Complete ... WHEN MATCHED and WHEN NOT MATCHED BY SOURCE|TARGET with
+	 * THEN/AND
+	 */
 	else if (TailMatches("WHEN", "MATCHED") ||
-			 TailMatches("WHEN", "NOT", "MATCHED"))
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE|TARGET"))
 		COMPLETE_WITH("THEN", "AND");
 
-	/* Complete ... WHEN MATCHED THEN with UPDATE SET/DELETE/DO NOTHING */
-	else if (TailMatches("WHEN", "MATCHED", "THEN"))
+	/* Complete ... WHEN NOT MATCHED with BY/THEN/AND */
+	else if (TailMatches("WHEN", "NOT", "MATCHED"))
+		COMPLETE_WITH("BY", "THEN", "AND");
+
+	/* Complete ... WHEN NOT MATCHED BY with SOURCE/TARGET */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "BY"))
+		COMPLETE_WITH("SOURCE", "TARGET");
+
+	/*
+	 * Complete ... WHEN MATCHED THEN and WHEN NOT MATCHED BY SOURCE THEN with
+	 * UPDATE SET/DELETE/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE", "THEN"))
 		COMPLETE_WITH("UPDATE SET", "DELETE", "DO NOTHING");
 
-	/* Complete ... WHEN NOT MATCHED THEN with INSERT/DO NOTHING */
-	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN"))
+	/*
+	 * Complete ... WHEN NOT MATCHED [BY TARGET] THEN with INSERT/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "TARGET", "THEN"))
 		COMPLETE_WITH("INSERT", "DO NOTHING");
 
 /* NOTIFY --- can be inside EXPLAIN, RULE, etc */
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
new file mode 100644
index b3bec90..65c3e55
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -183,8 +183,9 @@ typedef struct Query
 								 * also USING clause for MERGE */
 
 	List	   *mergeActionList;	/* list of actions for MERGE (only) */
-	/* whether to use outer join */
-	bool		mergeUseOuterJoin pg_node_attr(query_jumble_ignore);
+
+	/* rtable index of source relation for MERGE */
+	int			mergeSourceRelation pg_node_attr(query_jumble_ignore);
 
 	List	   *targetList;		/* target list (of TargetEntry) */
 
@@ -1662,6 +1663,14 @@ typedef struct CommonTableExpr
 	 ((Query *) (cte)->ctequery)->targetList : \
 	 ((Query *) (cte)->ctequery)->returningList)
 
+/* MATCHED/NOT MATCHED specification for WHEN clauses in a MERGE statement */
+typedef enum MergeMatchKind
+{
+	MERGE_WHEN_MATCHED,
+	MERGE_WHEN_NOT_MATCHED_BY_SOURCE,
+	MERGE_WHEN_NOT_MATCHED_BY_TARGET
+} MergeMatchKind;
+
 /*
  * MergeWhenClause -
  *		raw parser representation of a WHEN clause in a MERGE statement
@@ -1671,7 +1680,7 @@ typedef struct CommonTableExpr
 typedef struct MergeWhenClause
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *condition;		/* WHEN conditions (raw parser) */
@@ -1687,7 +1696,7 @@ typedef struct MergeWhenClause
 typedef struct MergeAction
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	/* OVERRIDING clause */
 	OverridingKind override pg_node_attr(query_jumble_ignore);
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
new file mode 100644
index f5b2e61..c34635d
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -401,6 +401,7 @@ PG_KEYWORD("skip", SKIP, UNRESERVED_KEYW
 PG_KEYWORD("smallint", SMALLINT, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("snapshot", SNAPSHOT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("some", SOME, RESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("source", SOURCE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("sql", SQL_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("stable", STABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("standalone", STANDALONE_P, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -424,6 +425,7 @@ PG_KEYWORD("table", TABLE, RESERVED_KEYW
 PG_KEYWORD("tables", TABLES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablesample", TABLESAMPLE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablespace", TABLESPACE, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("target", TARGET, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temp", TEMP, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("template", TEMPLATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temporary", TEMPORARY, UNRESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/test/regress/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index 133d421..0c35a35
--- a/src/test/regress/expected/merge.out
+++ b/src/test/regress/expected/merge.out
@@ -71,6 +71,15 @@ WHEN MATCHED THEN
 ERROR:  syntax error at or near "INSERT"
 LINE 5:  INSERT DEFAULT VALUES;
          ^
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
+ERROR:  syntax error at or near "INSERT"
+LINE 5:  INSERT DEFAULT VALUES;
+         ^
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -107,6 +116,15 @@ WHEN NOT MATCHED THEN
 ERROR:  syntax error at or near "UPDATE"
 LINE 5:  UPDATE SET balance = 0;
          ^
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
+ERROR:  syntax error at or near "UPDATE"
+LINE 5:  UPDATE SET balance = 0;
+         ^
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -271,6 +289,22 @@ SELECT * FROM target ORDER BY tid;
 (4 rows)
 
 ROLLBACK;
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   4 |      40
+(1 row)
+
+ROLLBACK;
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -738,6 +772,19 @@ SELECT * FROM wq_target;
    1 |      -1
 (1 row)
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+ERROR:  invalid reference to FROM-clause entry for table "s"
+LINE 3: WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+                                       ^
+DETAIL:  There is an entry for table "s", but it cannot be referenced from this part of the query.
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
  balance | sid 
@@ -923,6 +970,45 @@ SELECT * FROM target ORDER BY tid;
 (3 rows)
 
 ROLLBACK;
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE DELETE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  BEFORE INSERT ROW trigger row: (4,40)
+NOTICE:  BEFORE DELETE ROW trigger row: (2,20)
+NOTICE:  BEFORE UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  AFTER INSERT ROW trigger row: (4,40)
+NOTICE:  AFTER DELETE ROW trigger row: (2,20)
+NOTICE:  AFTER UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER DELETE STATEMENT trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |       0
+   3 |      10
+   4 |      40
+(3 rows)
+
+ROLLBACK;
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -1451,6 +1537,50 @@ WHEN NOT MATCHED AND s.a < 20 THEN
                ->  Seq Scan on ex_mtarget t (actual rows=49 loops=1)
 (12 rows)
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=54
+   ->  Merge Left Join (actual rows=54 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=100
+   ->  Merge Full Join (actual rows=100 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
new file mode 100644
index 7fd81e6..478e714
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -3670,7 +3670,39 @@ BEGIN ATOMIC
      THEN INSERT (filling[1], id)
       VALUES (s.a, s.a);
 END
+CREATE FUNCTION merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+   USING rule_merge1 s
+   ON (s.a = t.id)
+WHEN NOT MATCHED
+   THEN INSERT (data, id)
+   VALUES (s.a, s.a)
+WHEN MATCHED
+   THEN UPDATE SET data = s.b
+WHEN NOT MATCHED BY SOURCE
+   THEN DELETE;
+END;
+\sf merge_sf_test2
+CREATE OR REPLACE FUNCTION public.merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+    USING rule_merge1 s
+    ON (s.a = t.id)
+    WHEN NOT MATCHED BY TARGET
+     THEN INSERT (data, id)
+      VALUES (s.a, s.a)
+    WHEN MATCHED
+     THEN UPDATE SET data = s.b
+    WHEN NOT MATCHED BY SOURCE
+     THEN DELETE;
+END
 DROP FUNCTION merge_sf_test;
+DROP FUNCTION merge_sf_test2;
 DROP TABLE sf_target;
 --
 -- Test enabling/disabling
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index 4cf6db9..bd399ab
--- a/src/test/regress/sql/merge.sql
+++ b/src/test/regress/sql/merge.sql
@@ -51,6 +51,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN MATCHED THEN
 	INSERT DEFAULT VALUES;
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -75,6 +81,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN NOT MATCHED THEN
 	UPDATE SET balance = 0;
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -213,6 +225,18 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -497,6 +521,17 @@ WHEN NOT MATCHED AND s.balance = 100 THE
 	INSERT (tid) VALUES (s.sid);
 SELECT * FROM wq_target;
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
+
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
 MERGE INTO wq_target t
@@ -624,6 +659,25 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -929,6 +983,20 @@ WHEN MATCHED AND t.a >= 30 AND t.a <= 40
 WHEN NOT MATCHED AND s.a < 20 THEN
 	INSERT VALUES (a, b)');
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
diff --git a/src/test/regress/sql/rules.sql b/src/test/regress/sql/rules.sql
new file mode 100644
index 8b7e255..ae9141f
--- a/src/test/regress/sql/rules.sql
+++ b/src/test/regress/sql/rules.sql
@@ -1323,7 +1323,26 @@ END;
 
 \sf merge_sf_test
 
+CREATE FUNCTION merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+   USING rule_merge1 s
+   ON (s.a = t.id)
+WHEN NOT MATCHED
+   THEN INSERT (data, id)
+   VALUES (s.a, s.a)
+WHEN MATCHED
+   THEN UPDATE SET data = s.b
+WHEN NOT MATCHED BY SOURCE
+   THEN DELETE;
+END;
+
+\sf merge_sf_test2
+
 DROP FUNCTION merge_sf_test;
+DROP FUNCTION merge_sf_test2;
 DROP TABLE sf_target;
 
 --
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
new file mode 100644
index 2608547..303387c
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1548,6 +1548,7 @@ MergeAppendState
 MergeJoin
 MergeJoinClause
 MergeJoinState
+MergeMatchKind
 MergePath
 MergeScanSelCache
 MergeStmt

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
new file mode 100644
index f8f83d4..6ef0c2b
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -396,8 +396,8 @@
     originally matched appears later in the list of actions.
     On the other hand, if the row is concurrently updated or deleted so
     that the join condition fails, then <command>MERGE</command> will
-    evaluate the condition's <literal>NOT MATCHED</literal> actions next,
-    and execute the first one that succeeds.
+    evaluate the condition's <literal>NOT MATCHED [BY TARGET]</literal>
+    actions next, and execute the first one that succeeds.
     If <command>MERGE</command> attempts an <command>INSERT</command>
     and a unique index is present and a duplicate row is concurrently
     inserted, then a uniqueness violation error is raised;
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
new file mode 100644
index 655f7dc..f421716
--- a/doc/src/sgml/ref/merge.sgml
+++ b/doc/src/sgml/ref/merge.sgml
@@ -33,7 +33,8 @@ USING <replaceable class="parameter">dat
 <phrase>and <replaceable class="parameter">when_clause</replaceable> is:</phrase>
 
 { WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
-  WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
+  WHEN NOT MATCHED BY SOURCE [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
+  WHEN NOT MATCHED [BY TARGET] [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
 
 <phrase>and <replaceable class="parameter">merge_insert</replaceable> is:</phrase>
 
@@ -70,7 +71,9 @@ DELETE
    from <replaceable class="parameter">data_source</replaceable> to
    <replaceable class="parameter">target_table_name</replaceable>
    producing zero or more candidate change rows.  For each candidate change
-   row, the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal>
+   row, the status of <literal>MATCHED</literal>,
+   <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>
    is set just once, after which <literal>WHEN</literal> clauses are evaluated
    in the order specified.  For each candidate change row, the first clause to
    evaluate as true is executed.  No more than one <literal>WHEN</literal>
@@ -226,16 +229,37 @@ DELETE
       At least one <literal>WHEN</literal> clause is required.
      </para>
      <para>
+      The <literal>WHEN</literal> clause may specify <literal>WHEN MATCHED</literal>,
+      <literal>WHEN NOT MATCHED BY SOURCE</literal>, or
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>.
+      Note that the <acronym>SQL</acronym> standard only defines
+      <literal>WHEN MATCHED</literal> and <literal>WHEN NOT MATCHED</literal>
+      (which is defined to mean no matching target row).
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> is an extension to the
+      <acronym>SQL</acronym> standard, as is the option to append
+      <literal>BY TARGET</literal> to <literal>WHEN NOT MATCHED</literal>, to
+      make its meaning more explicit.
+     </para>
+     <para>
       If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
-      and the candidate change row matches a row in the
+      and the candidate change row matches a row in the source to a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
      </para>
      <para>
-      Conversely, if the <literal>WHEN</literal> clause specifies
-      <literal>WHEN NOT MATCHED</literal>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> and the candidate change
+      row represents a row in the
+      <replaceable class="parameter">target_table_name</replaceable> that does
+      not match a source row, the <literal>WHEN</literal> clause is executed
+      if the <replaceable class="parameter">condition</replaceable> is
+      absent or it evaluates to <literal>true</literal>.
+     </para>
+     <para>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>
       and the candidate change row does not match a row in the
       <replaceable class="parameter">target_table_name</replaceable>,
       the <literal>WHEN</literal> clause is executed if the
@@ -257,7 +281,10 @@ DELETE
      <para>
       A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
       in both the source and the target relations. A condition on a
-      <literal>WHEN NOT MATCHED</literal> clause can only refer to columns from
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> clause can only refer to
+      columns from the target relation, since by definition there is no matching
+      source row. A condition on a <literal>WHEN NOT MATCHED [BY TARGET]</literal>
+      clause can only refer to columns from
       the source relation, since by definition there is no matching target row.
       Only the system attributes from the target table are accessible.
      </para>
@@ -382,8 +409,10 @@ DELETE
       <literal>WHEN MATCHED</literal> clause, the expression can use values
       from the original row in the target table, and values from the
       <replaceable>data_source</replaceable> row.
-      If used in a <literal>WHEN NOT MATCHED</literal> clause, the
-      expression can use values from the <replaceable>data_source</replaceable>.
+      If used in a <literal>WHEN NOT MATCHED BY SOURCE</literal> clause, the
+      expression can only use values from the original row in the target table.
+      If used in a <literal>WHEN NOT MATCHED [BY TARGET]</literal> clause, the
+      expression can only use values from the <replaceable>data_source</replaceable>.
      </para>
     </listitem>
    </varlistentry>
@@ -452,8 +481,9 @@ MERGE <replaceable class="parameter">tot
        <orderedlist>
         <listitem>
          <para>
-          Evaluate whether each row is <literal>MATCHED</literal> or
-          <literal>NOT MATCHED</literal>.
+          Evaluate whether each row is <literal>MATCHED</literal>,
+          <literal>NOT MATCHED BY SOURCE</literal>, or
+          <literal>NOT MATCHED [BY TARGET]</literal>.
          </para>
         </listitem>
         <listitem>
@@ -528,7 +558,8 @@ MERGE <replaceable class="parameter">tot
   <para>
    If a <literal>WHEN</literal> clause omits an <literal>AND</literal>
    sub-clause, it becomes the final reachable clause of that
-   kind (<literal>MATCHED</literal> or <literal>NOT MATCHED</literal>).
+   kind (<literal>MATCHED</literal>, <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>).
    If a later <literal>WHEN</literal> clause of that kind
    is specified it would be provably unreachable and an error is raised.
    If no final reachable clause is specified of either kind, it is
@@ -619,6 +650,23 @@ WHEN MATCHED THEN
    temporary table recently loaded into the database.
   </para>
 
+  <para>
+   Update <literal>wine</literal> based on a replacement wine list, inserting
+   rows for any new stock, updating modified stock entries, and deleting any
+   wines not present in the new list.
+<programlisting>
+MERGE INTO wines w
+USING new_wine_list s
+ON s.winename = w.winename
+WHEN NOT MATCHED BY TARGET THEN
+  INSERT VALUES(s.winename, s.stock)
+WHEN MATCHED AND w.stock != s.stock THEN
+  UPDATE SET stock = s.stock
+WHEN NOT MATCHED BY SOURCE THEN
+  DELETE;
+</programlisting>
+  </para>
+
  </refsect1>
 
  <refsect1>
@@ -627,7 +675,9 @@ WHEN MATCHED THEN
     This command conforms to the <acronym>SQL</acronym> standard.
   </para>
    <para>
-    The <literal>WITH</literal> clause and <literal>DO NOTHING</literal>
+    The <literal>WITH</literal> clause, <literal>BY SOURCE</literal> and
+    <literal>BY TARGET</literal> qualifiers to
+    <literal>WHEN NOT MATCHED</literal>, and <literal>DO NOTHING</literal>
     action are extensions to the <acronym>SQL</acronym> standard.
   </para>
  </refsect1>
diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
new file mode 100644
index b22040a..b5a18d2
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -902,8 +902,16 @@ ExecInitPartitionInfo(ModifyTableState *
 			action_state = makeNode(MergeActionState);
 			action_state->mas_action = action;
 
-			/* And put the action in the appropriate list */
-			if (action->matched)
+			/*
+			 * Put the action in the appropriate list.
+			 *
+			 * Note that the executor treats WHEN NOT MATCHED BY SOURCE
+			 * actions in exactly the same way as WHEN MATCHED actions, since
+			 * they both match the target (see ExecMerge).  Thus both types go
+			 * in the "matched" list.  Only WHEN NOT MATCHED BY TARGET actions
+			 * go in the "not matched" list.
+			 */
+			if (action->matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET)
 				list = &leaf_part_rri->ri_matchedMergeAction;
 			else
 				list = &leaf_part_rri->ri_notMatchedMergeAction;
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
new file mode 100644
index 9fc5abf..8cb8933
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -24,13 +24,15 @@
  *		values plus row-locating info for UPDATE and MERGE cases, or just the
  *		row-locating info for DELETE cases.
  *
- *		MERGE runs a join between the source relation and the target
- *		table; if any WHEN NOT MATCHED clauses are present, then the
- *		join is an outer join.  In this case, any unmatched tuples will
- *		have NULL row-locating info, and only INSERT can be run. But for
- *		matched tuples, then row-locating info is used to determine the
- *		tuple to UPDATE or DELETE. When all clauses are WHEN MATCHED,
- *		then an inner join is used, so all tuples contain row-locating info.
+ *		MERGE runs a join between the source relation and the target table.
+ *		If any WHEN NOT MATCHED [BY TARGET] clauses are present, then the join
+ *		is an outer join that might output tuples without a matching target
+ *		tuple.  In this case, any unmatched target tuples will have NULL
+ *		row-locating info, and only INSERT can be run.  But for matched
+ *		target tuples, the row-locating info is used to determine the tuple
+ *		to UPDATE or DELETE.  When all clauses are WHEN MATCHED or WHEN NOT
+ *		MATCHED BY SOURCE, all tuples produced by the join will include a
+ *		matching target tuple, so all tuples contain row-locating info.
  *
  *		If the query specifies RETURNING, then the ModifyTable returns a
  *		RETURNING tuple after completing each row insert, update, or delete.
@@ -2721,6 +2723,17 @@ ExecMerge(ModifyTableContext *context, R
 	bool		matched;
 
 	/*-----
+	 * Note that as far as the executor is concerned, WHEN NOT MATCHED BY
+	 * SOURCE actions are treated exactly the same as WHEN MATCHED actions,
+	 * since both match target tuples.  They are distinguished from one
+	 * another by a qual that tests if the source tuple is NULL, but the
+	 * executor knows nothing about the contents of the merge action quals.
+	 * Thus WHEN MATCHED and WHEN NOT MATCHED BY SOURCE actions are stored
+	 * together in the same "matched" list.  Thus, in the dicussion that
+	 * follows "MATCHED" means "matched by target", and should be taken to
+	 * include both WHEN MATCHED and WHEN NOT MATCHED BY SOURCE, while "NOT
+	 * MATCHED" means NOT MATCHED BY TARGET.
+	 *
 	 * If we are dealing with a WHEN MATCHED case (tupleid is valid), we
 	 * execute the first action for which the additional WHEN MATCHED AND
 	 * quals pass.  If an action without quals is found, that action is
@@ -3065,9 +3078,13 @@ lmerge_matched:
 							 * is executed.
 							 *
 							 * Update tupleid to that of the new tuple, for
-							 * the refetch we do at the top.
+							 * the refetch we do at the top, and install the
+							 * updated plan slot in ecxt_innertuple in case
+							 * the source tuple is now NULL (a change from
+							 * MATCHED to NOT MATCHED BY SOURCE).
 							 */
 							ItemPointerCopy(&context->tmfd.ctid, tupleid);
+							econtext->ecxt_innertuple = epqslot;
 							goto lmerge_matched;
 
 						case TM_Deleted:
@@ -3272,8 +3289,14 @@ ExecInitMerge(ModifyTableState *mtstate,
 			 * We create two lists - one for WHEN MATCHED actions and one for
 			 * WHEN NOT MATCHED actions - and stick the MergeActionState into
 			 * the appropriate list.
+			 *
+			 * Note that the executor treats WHEN NOT MATCHED BY SOURCE
+			 * actions in exactly the same way as WHEN MATCHED actions, since
+			 * they both match the target (see ExecMerge).  Thus both types go
+			 * in the "matched" list.  Only WHEN NOT MATCHED BY TARGET actions
+			 * go in the "not matched" list.
 			 */
-			if (action_state->mas_action->matched)
+			if (action->matchKind != MERGE_WHEN_NOT_MATCHED_BY_TARGET)
 				list = &resultRelInfo->ri_matchedMergeAction;
 			else
 				list = &resultRelInfo->ri_notMatchedMergeAction;
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
new file mode 100644
index aa83dd3..38020bd
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -153,6 +153,8 @@ transform_MERGE_to_join(Query *parse)
 {
 	RangeTblEntry *joinrte;
 	JoinExpr   *joinexpr;
+	bool		src_only_tuples;
+	bool		tgt_only_tuples;
 	JoinType	jointype;
 	int			joinrti;
 	List	   *vars;
@@ -164,12 +166,30 @@ transform_MERGE_to_join(Query *parse)
 	vars = NIL;
 
 	/*
-	 * When any WHEN NOT MATCHED THEN INSERT clauses exist, we need to use an
-	 * outer join so that we process all unmatched tuples from the source
-	 * relation.  If none exist, we can use an inner join.
+	 * Work out what kind of join is required.  If there any WHEN NOT MATCHED
+	 * BY SOURCE/TARGET actions, an outer join is required so that we process
+	 * all unmatched tuples from the source and/or target relations.
+	 * Otherwise, we can use an inner join.
 	 */
-	if (parse->mergeUseOuterJoin)
+	src_only_tuples = false;
+	tgt_only_tuples = false;
+	foreach_node(MergeAction, action, parse->mergeActionList)
+	{
+		if (action->commandType != CMD_NOTHING)
+		{
+			if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+				tgt_only_tuples = true;
+			if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_TARGET)
+				src_only_tuples = true;
+		}
+	}
+
+	if (src_only_tuples && tgt_only_tuples)
+		jointype = JOIN_FULL;
+	else if (src_only_tuples)
 		jointype = JOIN_RIGHT;
+	else if (tgt_only_tuples)
+		jointype = JOIN_LEFT;
 	else
 		jointype = JOIN_INNER;
 
@@ -215,6 +235,50 @@ transform_MERGE_to_join(Query *parse)
 	/* Make the new join be the sole entry in the query's jointree */
 	parse->jointree->fromlist = list_make1(joinexpr);
 	parse->jointree->quals = NULL;
+
+	/*
+	 * If there any WHEN NOT MATCHED BY SOURCE actions that require unmatched
+	 * tuples from the target relation to be processed, add additional WHEN
+	 * conditions to every action to check whether tuples from the source
+	 * match or not, as necessary.
+	 *
+	 * This distinguishes WHEN NOT MATCHED BY SOURCE actions (identified by a
+	 * "source IS NOT DISTINCT FROM NULL" clause) from WHEN MATCHED actions
+	 * (identified by a "source IS DISTINCT FROM NULL" clause).
+	 *
+	 * Additionally, a "source IS DISTINCT FROM NULL" clause is required for
+	 * WHEN NOT MATCHED [BY TARGET] actions in case the executor attempts to
+	 * invoke such an action for a concurrently deleted target row that ends
+	 * up matching neither source nor target.
+	 */
+	if (tgt_only_tuples)
+	{
+		foreach_node(MergeAction, action, parse->mergeActionList)
+		{
+			bool		src_null;
+			Var		   *var;
+			NullTest   *ntest;
+
+			/* Make a "source IS [NOT] DISTINCT FROM NULL" clause */
+			src_null = action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE;
+
+			var = makeWholeRowVar(rt_fetch(parse->mergeSourceRelation,
+										   parse->rtable),
+								  parse->mergeSourceRelation, 0, false);
+
+			/* source wholerow Var is nullable by the new join */
+			var->varnullingrels = bms_make_singleton(joinrti);
+
+			ntest = makeNode(NullTest);
+			ntest->arg = (Expr *) var;
+			ntest->nulltesttype = src_null ? IS_NULL : IS_NOT_NULL;
+			ntest->argisrow = false;
+			ntest->location = -1;
+
+			/* Combine it with the action's WHEN condition */
+			action->qual = make_and_qual((Node *) ntest, action->qual);
+		}
+	}
 }
 
 /*
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index 130f7fc..f6b4c80
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -275,6 +275,7 @@ static Node *makeRecursiveViewSelect(cha
 	struct SelectLimit *selectlimit;
 	SetQuantifier setquantifier;
 	struct GroupClause *groupclause;
+	MergeMatchKind mergematch;
 	MergeWhenClause *mergewhen;
 	struct KeyActions *keyactions;
 	struct KeyAction *keyaction;
@@ -515,6 +516,7 @@ static Node *makeRecursiveViewSelect(cha
 %type <onconflict> opt_on_conflict
 %type <mergewhen>	merge_insert merge_update merge_delete
 
+%type <mergematch> merge_when_tgt_matched merge_when_tgt_not_matched
 %type <node>	merge_when_clause opt_merge_when_condition
 %type <list>	merge_when_list
 
@@ -759,11 +761,11 @@ static Node *makeRecursiveViewSelect(cha
 	SAVEPOINT SCALAR SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT
 	SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
-	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
+	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SOURCE SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRIP_P
 	SUBSCRIPTION SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
 
-	TABLE TABLES TABLESAMPLE TABLESPACE TEMP TEMPLATE TEMPORARY TEXT_P THEN
+	TABLE TABLES TABLESAMPLE TABLESPACE TARGET TEMP TEMPLATE TEMPORARY TEXT_P THEN
 	TIES TIME TIMESTAMP TO TRAILING TRANSACTION TRANSFORM
 	TREAT TRIGGER TRIM TRUE_P
 	TRUNCATE TRUSTED TYPE_P TYPES_P
@@ -12386,50 +12388,66 @@ merge_when_list:
 			| merge_when_list merge_when_clause		{ $$ = lappend($1,$2); }
 		;
 
+/*
+ * A WHEN clause may be WHEN MATCHED, WHEN NOT MATCHED BY SOURCE, or WHEN NOT
+ * MATCHED [BY TARGET]. The first two cases match target tuples, and support
+ * UPDATE/DELETE/DO NOTHING actions. The third case does not match target
+ * tuples, and only supports INSERT/DO NOTHING actions.
+ */
 merge_when_clause:
-			WHEN MATCHED opt_merge_when_condition THEN merge_update
+			merge_when_tgt_matched opt_merge_when_condition THEN merge_update
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN merge_delete
+			| merge_when_tgt_matched opt_merge_when_condition THEN merge_delete
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN merge_insert
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN merge_insert
 				{
-					$6->matched = false;
-					$6->condition = $4;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $6;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = true;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $3;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = false;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $4;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
 		;
 
+merge_when_tgt_matched:
+			WHEN MATCHED					{ $$ = MERGE_WHEN_MATCHED; }
+			| WHEN NOT MATCHED BY SOURCE	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_SOURCE; }
+		;
+
+merge_when_tgt_not_matched:
+			WHEN NOT MATCHED				{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+			| WHEN NOT MATCHED BY TARGET	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+		;
+
 opt_merge_when_condition:
 			AND a_expr				{ $$ = $2; }
 			|						{ $$ = NULL; }
@@ -17388,6 +17406,7 @@ unreserved_keyword:
 			| SIMPLE
 			| SKIP
 			| SNAPSHOT
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -17406,6 +17425,7 @@ unreserved_keyword:
 			| SYSTEM_P
 			| TABLES
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
@@ -18001,6 +18021,7 @@ bare_label_keyword:
 			| SMALLINT
 			| SNAPSHOT
 			| SOME
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -18024,6 +18045,7 @@ bare_label_keyword:
 			| TABLES
 			| TABLESAMPLE
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
diff --git a/src/backend/parser/parse_merge.c b/src/backend/parser/parse_merge.c
new file mode 100644
index 5f6a683..57902f5
--- a/src/backend/parser/parse_merge.c
+++ b/src/backend/parser/parse_merge.c
@@ -43,9 +43,9 @@ static void setNamespaceVisibilityForRTE
  * Make appropriate changes to the namespace visibility while transforming
  * individual action's quals and targetlist expressions. In particular, for
  * INSERT actions we must only see the source relation (since INSERT action is
- * invoked for NOT MATCHED tuples and hence there is no target tuple to deal
- * with). On the other hand, UPDATE and DELETE actions can see both source and
- * target relations.
+ * invoked for NOT MATCHED [BY TARGET] tuples and hence there is no target
+ * tuple to deal with). On the other hand, UPDATE and DELETE actions can see
+ * both source and target relations, unless invoked for NOT MATCHED BY SOURCE.
  *
  * Also, since the internal join node can hide the source and target
  * relations, we must explicitly make the respective relation as visible so
@@ -61,7 +61,7 @@ setNamespaceForMergeWhen(ParseState *pst
 	targetRelRTE = rt_fetch(targetRTI, pstate->p_rtable);
 	sourceRelRTE = rt_fetch(sourceRTI, pstate->p_rtable);
 
-	if (mergeWhenClause->matched)
+	if (mergeWhenClause->matchKind == MERGE_WHEN_MATCHED)
 	{
 		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
 			   mergeWhenClause->commandType == CMD_DELETE ||
@@ -73,11 +73,25 @@ setNamespaceForMergeWhen(ParseState *pst
 		setNamespaceVisibilityForRTE(pstate->p_namespace,
 									 sourceRelRTE, true, true);
 	}
-	else
+	else if (mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
 	{
 		/*
-		 * NOT MATCHED actions can't see target relation, but they can see
-		 * source relation.
+		 * NOT MATCHED BY SOURCE actions can see the target relation, but they
+		 * can't see the source relation.
+		 */
+		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
+			   mergeWhenClause->commandType == CMD_DELETE ||
+			   mergeWhenClause->commandType == CMD_NOTHING);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 targetRelRTE, true, true);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 sourceRelRTE, false, false);
+	}
+	else						/* MERGE_WHEN_NOT_MATCHED_BY_TARGET */
+	{
+		/*
+		 * NOT MATCHED [BY TARGET] actions can't see target relation, but they
+		 * can see source relation.
 		 */
 		Assert(mergeWhenClause->commandType == CMD_INSERT ||
 			   mergeWhenClause->commandType == CMD_NOTHING);
@@ -98,8 +112,7 @@ transformMergeStmt(ParseState *pstate, M
 	Query	   *qry = makeNode(Query);
 	ListCell   *l;
 	AclMode		targetPerms = ACL_NO_RIGHTS;
-	bool		is_terminal[2];
-	Index		sourceRTI;
+	bool		is_terminal[3];
 	List	   *mergeActionList;
 	Node	   *joinExpr;
 	ParseNamespaceItem *nsitem;
@@ -125,12 +138,12 @@ transformMergeStmt(ParseState *pstate, M
 	/*
 	 * Check WHEN clauses for permissions and sanity
 	 */
-	is_terminal[0] = false;
-	is_terminal[1] = false;
+	is_terminal[MERGE_WHEN_MATCHED] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
 	foreach(l, stmt->mergeWhenClauses)
 	{
 		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
-		int			when_type = (mergeWhenClause->matched ? 0 : 1);
 
 		/*
 		 * Collect action types so we can check target permissions
@@ -155,12 +168,12 @@ transformMergeStmt(ParseState *pstate, M
 		/*
 		 * Check for unreachable WHEN clauses
 		 */
-		if (is_terminal[when_type])
+		if (is_terminal[mergeWhenClause->matchKind])
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
 					 errmsg("unreachable WHEN clause specified after unconditional WHEN clause")));
 		if (mergeWhenClause->condition == NULL)
-			is_terminal[when_type] = true;
+			is_terminal[mergeWhenClause->matchKind] = true;
 	}
 
 	/*
@@ -193,8 +206,8 @@ transformMergeStmt(ParseState *pstate, M
 	/* Now transform the source relation to produce the source RTE. */
 	transformFromClause(pstate,
 						list_make1(stmt->sourceRelation));
-	sourceRTI = list_length(pstate->p_rtable);
-	nsitem = GetNSItemByRangeTablePosn(pstate, sourceRTI, 0);
+	qry->mergeSourceRelation = list_length(pstate->p_rtable);
+	nsitem = GetNSItemByRangeTablePosn(pstate, qry->mergeSourceRelation, 0);
 
 	/*
 	 * Check that the target table doesn't conflict with the source table.
@@ -255,11 +268,7 @@ transformMergeStmt(ParseState *pstate, M
 
 		action = makeNode(MergeAction);
 		action->commandType = mergeWhenClause->commandType;
-		action->matched = mergeWhenClause->matched;
-
-		/* Use an outer join if any INSERT actions exist in the command. */
-		if (action->commandType == CMD_INSERT)
-			qry->mergeUseOuterJoin = true;
+		action->matchKind = mergeWhenClause->matchKind;
 
 		/*
 		 * Set namespace for the specific action. This must be done before
@@ -267,7 +276,7 @@ transformMergeStmt(ParseState *pstate, M
 		 */
 		setNamespaceForMergeWhen(pstate, mergeWhenClause,
 								 qry->resultRelation,
-								 sourceRTI);
+								 qry->mergeSourceRelation);
 
 		/*
 		 * Transform the WHEN condition.
diff --git a/src/backend/rewrite/rewriteManip.c b/src/backend/rewrite/rewriteManip.c
new file mode 100644
index 76c97a5..c04174c
--- a/src/backend/rewrite/rewriteManip.c
+++ b/src/backend/rewrite/rewriteManip.c
@@ -496,9 +496,10 @@ OffsetVarNodes(Node *node, int offset, i
 		/*
 		 * If we are starting at a Query, and sublevels_up is zero, then we
 		 * must also fix rangetable indexes in the Query itself --- namely
-		 * resultRelation, exclRelIndex and rowMarks entries.  sublevels_up
-		 * cannot be zero when recursing into a subquery, so there's no need
-		 * to have the same logic inside OffsetVarNodes_walker.
+		 * resultRelation, mergeSourceRelation, exclRelIndex and rowMarks
+		 * entries.  sublevels_up cannot be zero when recursing into a
+		 * subquery, so there's no need to have the same logic inside
+		 * OffsetVarNodes_walker.
 		 */
 		if (sublevels_up == 0)
 		{
@@ -507,6 +508,9 @@ OffsetVarNodes(Node *node, int offset, i
 			if (qry->resultRelation)
 				qry->resultRelation += offset;
 
+			if (qry->mergeSourceRelation)
+				qry->mergeSourceRelation += offset;
+
 			if (qry->onConflict && qry->onConflict->exclRelIndex)
 				qry->onConflict->exclRelIndex += offset;
 
@@ -687,9 +691,10 @@ ChangeVarNodes(Node *node, int rt_index,
 		/*
 		 * If we are starting at a Query, and sublevels_up is zero, then we
 		 * must also fix rangetable indexes in the Query itself --- namely
-		 * resultRelation and rowMarks entries.  sublevels_up cannot be zero
-		 * when recursing into a subquery, so there's no need to have the same
-		 * logic inside ChangeVarNodes_walker.
+		 * resultRelation, mergeSourceRelation, exclRelIndex and rowMarks
+		 * entries.  sublevels_up cannot be zero when recursing into a
+		 * subquery, so there's no need to have the same logic inside
+		 * ChangeVarNodes_walker.
 		 */
 		if (sublevels_up == 0)
 		{
@@ -698,6 +703,9 @@ ChangeVarNodes(Node *node, int rt_index,
 			if (qry->resultRelation == rt_index)
 				qry->resultRelation = new_index;
 
+			if (qry->mergeSourceRelation == rt_index)
+				qry->mergeSourceRelation = new_index;
+
 			/* this is unlikely to ever be used, but ... */
 			if (qry->onConflict && qry->onConflict->exclRelIndex == rt_index)
 				qry->onConflict->exclRelIndex = new_index;
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
new file mode 100644
index b625f47..51a1a2a
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -7093,6 +7093,7 @@ get_merge_query_def(Query *query, depars
 	StringInfo	buf = context->buf;
 	RangeTblEntry *rte;
 	ListCell   *lc;
+	bool		haveNotMatchedBySource;
 
 	/* Insert the WITH clause if given */
 	get_with_clause(query, context);
@@ -7120,6 +7121,25 @@ get_merge_query_def(Query *query, depars
 						 -PRETTYINDENT_STD, PRETTYINDENT_STD, 2);
 	get_rule_expr(query->jointree->quals, context, false);
 
+	/*
+	 * Test for any NOT MATCHED BY SOURCE actions.  If there are none, then
+	 * any NOT MATCHED BY TARGET actions are output as "WHEN NOT MATCHED", per
+	 * SQL standard.  Otherwise, we have a non-SQL-standard query, so output
+	 * "BY SOURCE" / "BY TARGET" qualifiers for all NOT MATCHED actions, to be
+	 * more explicit.
+	 */
+	haveNotMatchedBySource = false;
+	foreach(lc, query->mergeActionList)
+	{
+		MergeAction *action = lfirst_node(MergeAction, lc);
+
+		if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+		{
+			haveNotMatchedBySource = true;
+			break;
+		}
+	}
+
 	/* Print each merge action */
 	foreach(lc, query->mergeActionList)
 	{
@@ -7127,7 +7147,24 @@ get_merge_query_def(Query *query, depars
 
 		appendContextKeyword(context, " WHEN ",
 							 -PRETTYINDENT_STD, PRETTYINDENT_STD, 2);
-		appendStringInfo(buf, "%sMATCHED", action->matched ? "" : "NOT ");
+		switch (action->matchKind)
+		{
+			case MERGE_WHEN_MATCHED:
+				appendStringInfo(buf, "MATCHED");
+				break;
+			case MERGE_WHEN_NOT_MATCHED_BY_SOURCE:
+				appendStringInfo(buf, "NOT MATCHED BY SOURCE");
+				break;
+			case MERGE_WHEN_NOT_MATCHED_BY_TARGET:
+				if (haveNotMatchedBySource)
+					appendStringInfo(buf, "NOT MATCHED BY TARGET");
+				else
+					appendStringInfo(buf, "NOT MATCHED");
+				break;
+			default:
+				elog(ERROR, "unrecognized matchKind: %d",
+					 (int) action->matchKind);
+		}
 
 		if (action->qual)
 		{
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
new file mode 100644
index ada711d..8349f11
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -4331,17 +4331,35 @@ psql_completion(const char *text, int st
 			 TailMatches("USING", MatchAny, MatchAny, "ON", MatchAny, MatchAny, MatchAny, "WHEN"))
 		COMPLETE_WITH("MATCHED", "NOT MATCHED");
 
-	/* Complete ... WHEN [NOT] MATCHED with THEN/AND */
+	/*
+	 * Complete ... WHEN MATCHED and WHEN NOT MATCHED BY SOURCE|TARGET with
+	 * THEN/AND
+	 */
 	else if (TailMatches("WHEN", "MATCHED") ||
-			 TailMatches("WHEN", "NOT", "MATCHED"))
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE|TARGET"))
 		COMPLETE_WITH("THEN", "AND");
 
-	/* Complete ... WHEN MATCHED THEN with UPDATE SET/DELETE/DO NOTHING */
-	else if (TailMatches("WHEN", "MATCHED", "THEN"))
+	/* Complete ... WHEN NOT MATCHED with BY/THEN/AND */
+	else if (TailMatches("WHEN", "NOT", "MATCHED"))
+		COMPLETE_WITH("BY", "THEN", "AND");
+
+	/* Complete ... WHEN NOT MATCHED BY with SOURCE/TARGET */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "BY"))
+		COMPLETE_WITH("SOURCE", "TARGET");
+
+	/*
+	 * Complete ... WHEN MATCHED THEN and WHEN NOT MATCHED BY SOURCE THEN with
+	 * UPDATE SET/DELETE/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE", "THEN"))
 		COMPLETE_WITH("UPDATE SET", "DELETE", "DO NOTHING");
 
-	/* Complete ... WHEN NOT MATCHED THEN with INSERT/DO NOTHING */
-	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN"))
+	/*
+	 * Complete ... WHEN NOT MATCHED [BY TARGET] THEN with INSERT/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "TARGET", "THEN"))
 		COMPLETE_WITH("INSERT", "DO NOTHING");
 
 /* NOTIFY --- can be inside EXPLAIN, RULE, etc */
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
new file mode 100644
index 476d55d..d9ed9ed
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -175,8 +175,9 @@ typedef struct Query
 								 * also USING clause for MERGE */
 
 	List	   *mergeActionList;	/* list of actions for MERGE (only) */
-	/* whether to use outer join */
-	bool		mergeUseOuterJoin pg_node_attr(query_jumble_ignore);
+
+	/* rtable index of source relation for MERGE */
+	int			mergeSourceRelation pg_node_attr(query_jumble_ignore);
 
 	List	   *targetList;		/* target list (of TargetEntry) */
 
@@ -1665,7 +1666,7 @@ typedef struct CommonTableExpr
 typedef struct MergeWhenClause
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *condition;		/* WHEN conditions (raw parser) */
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
new file mode 100644
index 4a15460..f7eebd8
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -1732,10 +1732,18 @@ typedef struct BooleanTest
  *
  * Transformed representation of a WHEN clause in a MERGE statement
  */
+
+typedef enum MergeMatchKind
+{
+	MERGE_WHEN_MATCHED,
+	MERGE_WHEN_NOT_MATCHED_BY_SOURCE,
+	MERGE_WHEN_NOT_MATCHED_BY_TARGET
+} MergeMatchKind;
+
 typedef struct MergeAction
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	/* OVERRIDING clause */
 	OverridingKind override pg_node_attr(query_jumble_ignore);
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
new file mode 100644
index 2331aca..b7d5515
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -403,6 +403,7 @@ PG_KEYWORD("skip", SKIP, UNRESERVED_KEYW
 PG_KEYWORD("smallint", SMALLINT, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("snapshot", SNAPSHOT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("some", SOME, RESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("source", SOURCE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("sql", SQL_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("stable", STABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("standalone", STANDALONE_P, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -426,6 +427,7 @@ PG_KEYWORD("table", TABLE, RESERVED_KEYW
 PG_KEYWORD("tables", TABLES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablesample", TABLESAMPLE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablespace", TABLESPACE, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("target", TARGET, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temp", TEMP, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("template", TEMPLATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temporary", TEMPORARY, UNRESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/test/regress/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index f87905f..b13eda0
--- a/src/test/regress/expected/merge.out
+++ b/src/test/regress/expected/merge.out
@@ -71,6 +71,15 @@ WHEN MATCHED THEN
 ERROR:  syntax error at or near "INSERT"
 LINE 5:  INSERT DEFAULT VALUES;
          ^
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
+ERROR:  syntax error at or near "INSERT"
+LINE 5:  INSERT DEFAULT VALUES;
+         ^
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -107,6 +116,15 @@ WHEN NOT MATCHED THEN
 ERROR:  syntax error at or near "UPDATE"
 LINE 5:  UPDATE SET balance = 0;
          ^
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
+ERROR:  syntax error at or near "UPDATE"
+LINE 5:  UPDATE SET balance = 0;
+         ^
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -271,6 +289,22 @@ SELECT * FROM target ORDER BY tid;
 (4 rows)
 
 ROLLBACK;
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   4 |      40
+(1 row)
+
+ROLLBACK;
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -738,6 +772,19 @@ SELECT * FROM wq_target;
    1 |      -1
 (1 row)
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+ERROR:  invalid reference to FROM-clause entry for table "s"
+LINE 3: WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+                                       ^
+DETAIL:  There is an entry for table "s", but it cannot be referenced from this part of the query.
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
  balance | sid 
@@ -923,6 +970,45 @@ SELECT * FROM target ORDER BY tid;
 (3 rows)
 
 ROLLBACK;
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE DELETE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  BEFORE INSERT ROW trigger row: (4,40)
+NOTICE:  BEFORE DELETE ROW trigger row: (2,20)
+NOTICE:  BEFORE UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  AFTER INSERT ROW trigger row: (4,40)
+NOTICE:  AFTER DELETE ROW trigger row: (2,20)
+NOTICE:  AFTER UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER DELETE STATEMENT trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |       0
+   3 |      10
+   4 |      40
+(3 rows)
+
+ROLLBACK;
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -1451,6 +1537,50 @@ WHEN NOT MATCHED AND s.a < 20 THEN
                ->  Seq Scan on ex_mtarget t (actual rows=49 loops=1)
 (12 rows)
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=54
+   ->  Merge Left Join (actual rows=54 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=100
+   ->  Merge Full Join (actual rows=100 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
new file mode 100644
index abc944e..f1c0094
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -3705,7 +3705,39 @@ BEGIN ATOMIC
      THEN INSERT (filling[1], id)
       VALUES (s.a, s.a);
 END
+CREATE FUNCTION merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+   USING rule_merge1 s
+   ON (s.a = t.id)
+WHEN NOT MATCHED
+   THEN INSERT (data, id)
+   VALUES (s.a, s.a)
+WHEN MATCHED
+   THEN UPDATE SET data = s.b
+WHEN NOT MATCHED BY SOURCE
+   THEN DELETE;
+END;
+\sf merge_sf_test2
+CREATE OR REPLACE FUNCTION public.merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+    USING rule_merge1 s
+    ON (s.a = t.id)
+    WHEN NOT MATCHED BY TARGET
+     THEN INSERT (data, id)
+      VALUES (s.a, s.a)
+    WHEN MATCHED
+     THEN UPDATE SET data = s.b
+    WHEN NOT MATCHED BY SOURCE
+     THEN DELETE;
+END
 DROP FUNCTION merge_sf_test;
+DROP FUNCTION merge_sf_test2;
 DROP TABLE sf_target;
 --
 -- Test enabling/disabling
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index 66cb75a..7e59c9e
--- a/src/test/regress/sql/merge.sql
+++ b/src/test/regress/sql/merge.sql
@@ -51,6 +51,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN MATCHED THEN
 	INSERT DEFAULT VALUES;
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -75,6 +81,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN NOT MATCHED THEN
 	UPDATE SET balance = 0;
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -213,6 +225,18 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -497,6 +521,17 @@ WHEN NOT MATCHED AND s.balance = 100 THE
 	INSERT (tid) VALUES (s.sid);
 SELECT * FROM wq_target;
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
+
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
 MERGE INTO wq_target t
@@ -624,6 +659,25 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -929,6 +983,20 @@ WHEN MATCHED AND t.a >= 30 AND t.a <= 40
 WHEN NOT MATCHED AND s.a < 20 THEN
 	INSERT VALUES (a, b)');
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
diff --git a/src/test/regress/sql/rules.sql b/src/test/regress/sql/rules.sql
new file mode 100644
index 93aff4e..4ea85a2
--- a/src/test/regress/sql/rules.sql
+++ b/src/test/regress/sql/rules.sql
@@ -1323,7 +1323,26 @@ END;
 
 \sf merge_sf_test
 
+CREATE FUNCTION merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+   USING rule_merge1 s
+   ON (s.a = t.id)
+WHEN NOT MATCHED
+   THEN INSERT (data, id)
+   VALUES (s.a, s.a)
+WHEN MATCHED
+   THEN UPDATE SET data = s.b
+WHEN NOT MATCHED BY SOURCE
+   THEN DELETE;
+END;
+
+\sf merge_sf_test2
+
 DROP FUNCTION merge_sf_test;
+DROP FUNCTION merge_sf_test2;
 DROP TABLE sf_target;
 
 --
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
new file mode 100644
index 7e866e3..7892693
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1570,6 +1570,7 @@ MergeAppendState
 MergeJoin
 MergeJoinClause
 MergeJoinState
+MergeMatchKind
 MergePath
 MergeScanSelCache
 MergeStmt

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
new file mode 100644
index f8f83d4..380d0c9
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -394,10 +394,14 @@
     conditions for each action are re-evaluated on the updated version of
     the row, starting from the first action, even if the action that had
     originally matched appears later in the list of actions.
-    On the other hand, if the row is concurrently updated or deleted so
-    that the join condition fails, then <command>MERGE</command> will
-    evaluate the condition's <literal>NOT MATCHED</literal> actions next,
-    and execute the first one that succeeds.
+    On the other hand, if the row is concurrently updated so that the join
+    condition fails, then <command>MERGE</command> will evaluate the
+    command's <literal>NOT MATCHED BY SOURCE</literal> and
+    <literal>NOT MATCHED [BY TARGET]</literal> actions next, and execute
+    the first one of each kind that succeeds.
+    If the row is concurrently deleted, then <command>MERGE</command>
+    will evaluate the command's <literal>NOT MATCHED [BY TARGET]</literal>
+    actions, and execute the first one that succeeds.
     If <command>MERGE</command> attempts an <command>INSERT</command>
     and a unique index is present and a duplicate row is concurrently
     inserted, then a uniqueness violation error is raised;
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
new file mode 100644
index 7a8ac40..8935d2c
--- a/doc/src/sgml/ref/merge.sgml
+++ b/doc/src/sgml/ref/merge.sgml
@@ -33,7 +33,8 @@ USING <replaceable class="parameter">dat
 <phrase>and <replaceable class="parameter">when_clause</replaceable> is:</phrase>
 
 { WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
-  WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
+  WHEN NOT MATCHED BY SOURCE [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
+  WHEN NOT MATCHED [BY TARGET] [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
 
 <phrase>and <replaceable class="parameter">merge_insert</replaceable> is:</phrase>
 
@@ -70,7 +71,9 @@ DELETE
    from <replaceable class="parameter">data_source</replaceable> to
    the target table
    producing zero or more candidate change rows.  For each candidate change
-   row, the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal>
+   row, the status of <literal>MATCHED</literal>,
+   <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>
    is set just once, after which <literal>WHEN</literal> clauses are evaluated
    in the order specified.  For each candidate change row, the first clause to
    evaluate as true is executed.  No more than one <literal>WHEN</literal>
@@ -239,18 +242,40 @@ DELETE
       At least one <literal>WHEN</literal> clause is required.
      </para>
      <para>
+      The <literal>WHEN</literal> clause may specify <literal>WHEN MATCHED</literal>,
+      <literal>WHEN NOT MATCHED BY SOURCE</literal>, or
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>.
+      Note that the <acronym>SQL</acronym> standard only defines
+      <literal>WHEN MATCHED</literal> and <literal>WHEN NOT MATCHED</literal>
+      (which is defined to mean no matching target row).
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> is an extension to the
+      <acronym>SQL</acronym> standard, as is the option to append
+      <literal>BY TARGET</literal> to <literal>WHEN NOT MATCHED</literal>, to
+      make its meaning more explicit.
+     </para>
+     <para>
       If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
       and the candidate change row matches a row in the
-      target table,
-      the <literal>WHEN</literal> clause is executed if the
+      <replaceable class="parameter">data_source</replaceable> to a row in the
+      target table, the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
      </para>
      <para>
-      Conversely, if the <literal>WHEN</literal> clause specifies
-      <literal>WHEN NOT MATCHED</literal>
-      and the candidate change row does not match a row in the
-      target table,
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> and the candidate change
+      row represents a row in the target table that does not match a row in the
+      <replaceable class="parameter">data_source</replaceable>, the
+      <literal>WHEN</literal> clause is executed if the
+      <replaceable class="parameter">condition</replaceable> is
+      absent or it evaluates to <literal>true</literal>.
+     </para>
+     <para>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal> and the candidate change
+      row represents a row in the
+      <replaceable class="parameter">data_source</replaceable> that does not
+      match a row in the target table,
       the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
@@ -270,7 +295,10 @@ DELETE
      <para>
       A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
       in both the source and the target relations. A condition on a
-      <literal>WHEN NOT MATCHED</literal> clause can only refer to columns from
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> clause can only refer to
+      columns from the target relation, since by definition there is no matching
+      source row. A condition on a <literal>WHEN NOT MATCHED [BY TARGET]</literal>
+      clause can only refer to columns from
       the source relation, since by definition there is no matching target row.
       Only the system attributes from the target table are accessible.
      </para>
@@ -394,8 +422,10 @@ DELETE
       <literal>WHEN MATCHED</literal> clause, the expression can use values
       from the original row in the target table, and values from the
       <replaceable>data_source</replaceable> row.
-      If used in a <literal>WHEN NOT MATCHED</literal> clause, the
-      expression can use values from the <replaceable>data_source</replaceable>.
+      If used in a <literal>WHEN NOT MATCHED BY SOURCE</literal> clause, the
+      expression can only use values from the original row in the target table.
+      If used in a <literal>WHEN NOT MATCHED [BY TARGET]</literal> clause, the
+      expression can only use values from the <replaceable>data_source</replaceable>.
      </para>
     </listitem>
    </varlistentry>
@@ -464,8 +494,9 @@ MERGE <replaceable class="parameter">tot
        <orderedlist>
         <listitem>
          <para>
-          Evaluate whether each row is <literal>MATCHED</literal> or
-          <literal>NOT MATCHED</literal>.
+          Evaluate whether each row is <literal>MATCHED</literal>,
+          <literal>NOT MATCHED BY SOURCE</literal>, or
+          <literal>NOT MATCHED [BY TARGET]</literal>.
          </para>
         </listitem>
         <listitem>
@@ -544,7 +575,8 @@ MERGE <replaceable class="parameter">tot
   <para>
    If a <literal>WHEN</literal> clause omits an <literal>AND</literal>
    sub-clause, it becomes the final reachable clause of that
-   kind (<literal>MATCHED</literal> or <literal>NOT MATCHED</literal>).
+   kind (<literal>MATCHED</literal>, <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>).
    If a later <literal>WHEN</literal> clause of that kind
    is specified it would be provably unreachable and an error is raised.
    If no final reachable clause is specified of either kind, it is
@@ -635,6 +667,23 @@ WHEN MATCHED THEN
    temporary table recently loaded into the database.
   </para>
 
+  <para>
+   Update <literal>wines</literal> based on a replacement wine list, inserting
+   rows for any new stock, updating modified stock entries, and deleting any
+   wines not present in the new list.
+<programlisting>
+MERGE INTO wines w
+USING new_wine_list s
+ON s.winename = w.winename
+WHEN NOT MATCHED BY TARGET THEN
+  INSERT VALUES(s.winename, s.stock)
+WHEN MATCHED AND w.stock != s.stock THEN
+  UPDATE SET stock = s.stock
+WHEN NOT MATCHED BY SOURCE THEN
+  DELETE;
+</programlisting>
+  </para>
+
  </refsect1>
 
  <refsect1>
@@ -643,7 +692,9 @@ WHEN MATCHED THEN
     This command conforms to the <acronym>SQL</acronym> standard.
   </para>
    <para>
-    The <literal>WITH</literal> clause and <literal>DO NOTHING</literal>
+    The <literal>WITH</literal> clause, <literal>BY SOURCE</literal> and
+    <literal>BY TARGET</literal> qualifiers to
+    <literal>WHEN NOT MATCHED</literal>, and <literal>DO NOTHING</literal>
     action are extensions to the <acronym>SQL</acronym> standard.
   </para>
  </refsect1>
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
new file mode 100644
index 79ef46f..0ffd707
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -1254,8 +1254,10 @@ InitResultRelInfo(ResultRelInfo *resultR
 	resultRelInfo->ri_ReturningSlot = NULL;
 	resultRelInfo->ri_TrigOldSlot = NULL;
 	resultRelInfo->ri_TrigNewSlot = NULL;
-	resultRelInfo->ri_matchedMergeAction = NIL;
-	resultRelInfo->ri_notMatchedMergeAction = NIL;
+	resultRelInfo->ri_MergeActions[MERGE_WHEN_MATCHED] = NIL;
+	resultRelInfo->ri_MergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = NIL;
+	resultRelInfo->ri_MergeActions[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = NIL;
+	resultRelInfo->ri_MergeJoinCondition = NULL;
 
 	/*
 	 * Only ExecInitPartitionInfo() and ExecInitPartitionDispatchInfo() pass
diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
new file mode 100644
index 429f0a8..059ae5c
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -881,6 +881,7 @@ ExecInitPartitionInfo(ModifyTableState *
 		List	   *firstMergeActionList = linitial(node->mergeActionLists);
 		ListCell   *lc;
 		ExprContext *econtext = mtstate->ps.ps_ExprContext;
+		Node	   *joinCondition;
 
 		if (part_attmap == NULL)
 			part_attmap =
@@ -891,23 +892,31 @@ ExecInitPartitionInfo(ModifyTableState *
 		if (unlikely(!leaf_part_rri->ri_projectNewInfoValid))
 			ExecInitMergeTupleSlots(mtstate, leaf_part_rri);
 
+		/* Initialize state for join condition-checking. */
+		joinCondition =
+			map_variable_attnos(linitial(node->mergeJoinConditions),
+								firstVarno, 0,
+								part_attmap,
+								RelationGetForm(partrel)->reltype,
+								&found_whole_row);
+		/* We ignore the value of found_whole_row. */
+		leaf_part_rri->ri_MergeJoinCondition =
+			ExecInitQual((List *) joinCondition, &mtstate->ps);
+
 		foreach(lc, firstMergeActionList)
 		{
 			/* Make a copy for this relation to be safe.  */
 			MergeAction *action = copyObject(lfirst(lc));
 			MergeActionState *action_state;
-			List	  **list;
 
 			/* Generate the action's state for this relation */
 			action_state = makeNode(MergeActionState);
 			action_state->mas_action = action;
 
 			/* And put the action in the appropriate list */
-			if (action->matched)
-				list = &leaf_part_rri->ri_matchedMergeAction;
-			else
-				list = &leaf_part_rri->ri_notMatchedMergeAction;
-			*list = lappend(*list, action_state);
+			leaf_part_rri->ri_MergeActions[action->matchKind] =
+				lappend(leaf_part_rri->ri_MergeActions[action->matchKind],
+						action_state);
 
 			switch (action->commandType)
 			{
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
new file mode 100644
index ff7ec84..c22b0ea
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -24,13 +24,15 @@
  *		values plus row-locating info for UPDATE and MERGE cases, or just the
  *		row-locating info for DELETE cases.
  *
- *		MERGE runs a join between the source relation and the target
- *		table; if any WHEN NOT MATCHED clauses are present, then the
- *		join is an outer join.  In this case, any unmatched tuples will
- *		have NULL row-locating info, and only INSERT can be run. But for
- *		matched tuples, then row-locating info is used to determine the
- *		tuple to UPDATE or DELETE. When all clauses are WHEN MATCHED,
- *		then an inner join is used, so all tuples contain row-locating info.
+ *		MERGE runs a join between the source relation and the target table.
+ *		If any WHEN NOT MATCHED [BY TARGET] clauses are present, then the join
+ *		is an outer join that might output tuples without a matching target
+ *		tuple.  In this case, any unmatched target tuples will have NULL
+ *		row-locating info, and only INSERT can be run.  But for matched
+ *		target tuples, the row-locating info is used to determine the tuple
+ *		to UPDATE or DELETE.  When all clauses are WHEN MATCHED or WHEN NOT
+ *		MATCHED BY SOURCE, all tuples produced by the join will include a
+ *		matching target tuple, so all tuples contain row-locating info.
  *
  *		If the query specifies RETURNING, then the ModifyTable returns a
  *		RETURNING tuple after completing each row insert, update, or delete.
@@ -2719,48 +2721,61 @@ ExecMerge(ModifyTableContext *context, R
 	bool		matched;
 
 	/*-----
-	 * If we are dealing with a WHEN MATCHED case (tupleid or oldtuple is
-	 * valid, depending on whether the result relation is a table or a view),
-	 * we execute the first action for which the additional WHEN MATCHED AND
+	 * If we are dealing with a WHEN MATCHED case, tupleid or oldtuple is
+	 * valid, depending on whether the result relation is a table or a view.
+	 * We execute the first action for which the additional WHEN MATCHED AND
 	 * quals pass.  If an action without quals is found, that action is
 	 * executed.
 	 *
-	 * Similarly, if we are dealing with WHEN NOT MATCHED case, we look at
-	 * the given WHEN NOT MATCHED actions in sequence until one passes.
+	 * Similarly, in the WHEN NOT MATCHED BY SOURCE case, tupleid or oldtuple
+	 * is valid, and we look at the given WHEN NOT MATCHED BY SOURCE actions
+	 * in sequence until one passes.  This is almost identical to the WHEN
+	 * MATCHED case, and both cases are handled by ExecMergeMatched().
+	 *
+	 * Finally, in the WHEN NOT MATCHED [BY TARGET] case, both tupleid and
+	 * oldtuple are invalid, and we look at the given WHEN NOT MATCHED [BY
+	 * TARGET] actions in sequence until one passes.
 	 *
 	 * Things get interesting in case of concurrent update/delete of the
 	 * target tuple. Such concurrent update/delete is detected while we are
-	 * executing a WHEN MATCHED action.
+	 * executing a WHEN MATCHED or WHEN NOT MATCHED BY SOURCE action.
 	 *
 	 * A concurrent update can:
 	 *
 	 * 1. modify the target tuple so that it no longer satisfies the
-	 *    additional quals attached to the current WHEN MATCHED action
+	 *    additional quals attached to the current WHEN MATCHED or WHEN NOT
+	 *    MATCHED BY SOURCE action, but still satisfies the join quals.
 	 *
-	 *    In this case, we are still dealing with a WHEN MATCHED case.
-	 *    We recheck the list of WHEN MATCHED actions from the start and
-	 *    choose the first one that satisfies the new target tuple.
+	 *    In this case, we are still dealing with the same kind of match
+	 *    (MATCHED or NOT MATCHED BY SOURCE).  We recheck the same list of
+	 *    actions from the start and choose the first one that satisfies the
+	 *    new target tuple.
 	 *
 	 * 2. modify the target tuple so that the join quals no longer pass and
-	 *    hence the source tuple no longer has a match.
+	 *    hence the source and target tuples no longer match.
 	 *
-	 *    In this case, the source tuple no longer matches the target tuple,
-	 *    so we now instead find a qualifying WHEN NOT MATCHED action to
-	 *    execute.
+	 *    In this case, we are now dealing with a NOT MATCHED case, and we
+	 *    process both WHEN NOT MATCHED BY SOURCE and WHEN NOT MATCHED [BY
+	 *    TARGET] actions.  First ExecMergeMatched() processes the list of
+	 *    WHEN NOT MATCHED BY SOURCE actions in sequence until one passes,
+	 *    then ExecMergeNotMatched() processes any WHEN NOT MATCHED [BY
+	 *    TARGET] actions in sequence until one passes.  Thus we may execute
+	 *    two actions; one of each kind.
 	 *
 	 * XXX Hmmm, what if the updated tuple would now match one that was
 	 * considered NOT MATCHED so far?
 	 *
-	 * A concurrent delete changes a WHEN MATCHED case to WHEN NOT MATCHED.
+	 * A concurrent delete changes a WHEN MATCHED case to WHEN NOT MATCHED
+	 * [BY TARGET].
 	 *
 	 * ExecMergeMatched takes care of following the update chain and
-	 * re-finding the qualifying WHEN MATCHED action, as long as the updated
-	 * target tuple still satisfies the join quals, i.e., it remains a WHEN
-	 * MATCHED case. If the tuple gets deleted or the join quals fail, it
-	 * returns and we try ExecMergeNotMatched. Given that ExecMergeMatched
-	 * always make progress by following the update chain and we never switch
-	 * from ExecMergeNotMatched to ExecMergeMatched, there is no risk of a
-	 * livelock.
+	 * re-finding the qualifying WHEN MATCHED or WHEN NOT MATCHED BY SOURCE
+	 * action, as long as the target tuple still exists. If the target tuple
+	 * gets deleted or a concurrent update causes the join quals to fail, it
+	 * returns a matched status of false and we call ExecMergeNotMatched.
+	 * Given that ExecMergeMatched always makes progress by following the
+	 * update chain and we never switch from ExecMergeNotMatched to
+	 * ExecMergeMatched, there is no risk of a livelock.
 	 */
 	matched = tupleid != NULL || oldtuple != NULL;
 	if (matched)
@@ -2780,85 +2795,103 @@ ExecMerge(ModifyTableContext *context, R
 }
 
 /*
- * Check and execute the first qualifying MATCHED action.  If the target
+ * Check and execute the first qualifying MATCHED or NOT MATCHED BY SOURCE
+ * action, depending on whether the join quals are satisfied.  If the target
  * relation is a table, the current target tuple is identified by tupleid.
  * Otherwise, if the target relation is a view, oldtuple is the current target
  * tuple from the view.
  *
- * We start from the first WHEN MATCHED action and check if the WHEN quals
- * pass, if any. If the WHEN quals for the first action do not pass, we
- * check the second, then the third and so on. If we reach to the end, no
- * action is taken and we return true, indicating that no further action is
- * required for this tuple.
+ * We start from the first WHEN MATCHED or WHEN NOT MATCHED BY SOURCE action
+ * and check if the WHEN quals pass, if any. If the WHEN quals for the first
+ * action do not pass, we check the second, then the third and so on. If we
+ * reach to the end, no action is taken and we return true, indicating that no
+ * further action is required for this tuple.
  *
  * If we do find a qualifying action, then we attempt to execute the action.
  *
- * If the tuple is concurrently updated, EvalPlanQual is run with the updated
- * tuple to recheck the join quals. Note that the additional quals associated
- * with individual actions are evaluated by this routine via ExecQual, while
- * EvalPlanQual checks for the join quals. If EvalPlanQual tells us that the
- * updated tuple still passes the join quals, then we restart from the first
- * action to look for a qualifying action. Otherwise, we return false --
- * meaning that a NOT MATCHED action must now be executed for the current
- * source tuple.
+ * If the tuple is concurrently updated, and we were dealing with the MATCHED
+ * case, EvalPlanQual is run with the updated tuple to recheck the join quals.
+ * If the join quals no longer pass, we switch from the MATCHED case to the
+ * WHEN NOT MATCHED BY SOURCE case. Then we restart from the first action to
+ * look for a qualifying action. If we switched from matched to not matched,
+ * then we return false, indicating that a NOT MATCHED [BY TARGET] action must
+ * now be executed for the current source tuple (possibly in addition to any
+ * NOT MATCHED BY SOURCE action executed here).
  */
 static bool
 ExecMergeMatched(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
 				 ItemPointer tupleid, HeapTuple oldtuple, bool canSetTag)
 {
 	ModifyTableState *mtstate = context->mtstate;
+	List	  **mergeActions = resultRelInfo->ri_MergeActions;
+	List	   *actionStates;
 	TupleTableSlot *newslot;
 	EState	   *estate = context->estate;
 	ExprContext *econtext = mtstate->ps.ps_ExprContext;
 	bool		isNull;
 	EPQState   *epqstate = &mtstate->mt_epqstate;
+	bool		epq_ok;
 	ListCell   *l;
 
 	/*
-	 * If there are no WHEN MATCHED actions, we are done.
+	 * If there are no WHEN MATCHED or WHEN NOT MATCHED BY SOURCE actions, we
+	 * are done.
 	 */
-	if (resultRelInfo->ri_matchedMergeAction == NIL)
+	if (mergeActions[MERGE_WHEN_MATCHED] == NIL &&
+		mergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] == NIL)
 		return true;
 
 	/*
 	 * Make tuple and any needed join variables available to ExecQual and
 	 * ExecProject. The target's existing tuple is installed in the scantuple.
-	 * Again, this target relation's slot is required only in the case of a
-	 * MATCHED tuple and UPDATE/DELETE actions.
+	 * This target relation's slot is required only in the case of a MATCHED
+	 * or NOT MATCHED BY SOURCE tuple and UPDATE/DELETE actions.
 	 */
 	econtext->ecxt_scantuple = resultRelInfo->ri_oldTupleSlot;
 	econtext->ecxt_innertuple = context->planSlot;
 	econtext->ecxt_outertuple = NULL;
 
 	/*
-	 * This routine is only invoked for matched rows, so we should either have
-	 * the tupleid of the target row, or an old tuple from the target wholerow
-	 * junk attr.
+	 * This routine is only invoked for matched target rows, so we should
+	 * either have the tupleid of the target row, or an old tuple from the
+	 * target wholerow junk attr.
 	 */
 	Assert(tupleid != NULL || oldtuple != NULL);
 	if (oldtuple != NULL)
 		ExecForceStoreHeapTuple(oldtuple, resultRelInfo->ri_oldTupleSlot,
 								false);
-
-lmerge_matched:
+	else if (!table_tuple_fetch_row_version(resultRelInfo->ri_RelationDesc,
+											tupleid,
+											SnapshotAny,
+											resultRelInfo->ri_oldTupleSlot))
+		elog(ERROR, "failed to fetch the target tuple");
 
 	/*
-	 * If passed a tupleid, use it to fetch the old target row.
+	 * Test the join condition.  If it's satisfied, perform a MATCHED action;
+	 * otherwise, perform a NOT MATCHED BY SOURCE action.
 	 *
-	 * We use SnapshotAny for this because we might get called again after
-	 * EvalPlanQual returns us a new tuple, which may not be visible to our
-	 * MVCC snapshot.
+	 * Note that this join condition will be NULL if there are no NOT MATCHED
+	 * BY SOURCE actions --- see transform_MERGE_to_join().  In that case, the
+	 * join subplan will only output MATCHED and NOT MATCHED [BY TARGET] rows,
+	 * and we only need to process MATCHED actions here.
 	 */
-	if (tupleid != NULL)
-	{
-		if (!table_tuple_fetch_row_version(resultRelInfo->ri_RelationDesc,
-										   tupleid,
-										   SnapshotAny,
-										   resultRelInfo->ri_oldTupleSlot))
-			elog(ERROR, "failed to fetch the target tuple");
-	}
+	if (ExecQual(resultRelInfo->ri_MergeJoinCondition, econtext))
+		actionStates = mergeActions[MERGE_WHEN_MATCHED];
+	else
+		actionStates = mergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE];
 
-	foreach(l, resultRelInfo->ri_matchedMergeAction)
+	/*
+	 * A concurrent update may change the target tuple so that a MATCHED row
+	 * becomes NOT MATCHED BY SOURCE (but not vice versa).  If this happens,
+	 * we set epq_ok = false, process the NOT MATCHED BY SOURCE actions, and
+	 * then return false to indicate that the caller must also process any NOT
+	 * MATCHED [BY TARGET] actions.
+	 */
+	epq_ok = true;
+
+lmerge_matched:
+
+	foreach(l, actionStates)
 	{
 		MergeActionState *relaction = (MergeActionState *) lfirst(l);
 		CmdType		commandType = relaction->mas_action->commandType;
@@ -2913,7 +2946,7 @@ lmerge_matched:
 										tupleid, NULL, newslot, &result))
 				{
 					if (result == TM_Ok)
-						return true;	/* "do nothing" */
+						return epq_ok;	/* "do nothing" */
 					break;		/* concurrent update/delete */
 				}
 
@@ -2923,7 +2956,7 @@ lmerge_matched:
 				{
 					if (!ExecIRUpdateTriggers(estate, resultRelInfo,
 											  oldtuple, newslot))
-						return true;	/* "do nothing" */
+						return epq_ok;	/* "do nothing" */
 				}
 				else
 				{
@@ -2941,7 +2974,7 @@ lmerge_matched:
 					if (updateCxt.crossPartUpdate)
 					{
 						mtstate->mt_merge_updated += 1;
-						return true;
+						return epq_ok;
 					}
 				}
 
@@ -2959,7 +2992,7 @@ lmerge_matched:
 										NULL, NULL, &result))
 				{
 					if (result == TM_Ok)
-						return true;	/* "do nothing" */
+						return epq_ok;	/* "do nothing" */
 					break;		/* concurrent update/delete */
 				}
 
@@ -2969,7 +3002,7 @@ lmerge_matched:
 				{
 					if (!ExecIRDeleteTriggers(estate, resultRelInfo,
 											  oldtuple))
-						return true;	/* "do nothing" */
+						return epq_ok;	/* "do nothing" */
 				}
 				else
 					result = ExecDeleteAct(context, resultRelInfo, tupleid,
@@ -2989,7 +3022,7 @@ lmerge_matched:
 				break;
 
 			default:
-				elog(ERROR, "unknown action in MERGE WHEN MATCHED clause");
+				elog(ERROR, "unknown action in MERGE WHEN clause");
 		}
 
 		switch (result)
@@ -3025,12 +3058,13 @@ lmerge_matched:
 
 				/*
 				 * If the tuple was already deleted, return to let caller
-				 * handle it under NOT MATCHED clauses.
+				 * handle it under NOT MATCHED [BY TARGET] clauses.
 				 */
 				return false;
 
 			case TM_Updated:
 				{
+					bool		was_matched;
 					Relation	resultRelationDesc;
 					TupleTableSlot *epqslot,
 							   *inputslot;
@@ -3038,19 +3072,22 @@ lmerge_matched:
 
 					/*
 					 * The target tuple was concurrently updated by some other
-					 * transaction. Run EvalPlanQual() with the new version of
-					 * the tuple. If it does not return a tuple, then we
-					 * switch to the NOT MATCHED list of actions. If it does
-					 * return a tuple and the join qual is still satisfied,
-					 * then we just need to recheck the MATCHED actions,
-					 * starting from the top, and execute the first qualifying
-					 * action.
+					 * transaction.  If we are currently processing a MATCHED
+					 * action, use EvalPlanQual() with the new version of the
+					 * tuple and recheck the join qual, to detect a change
+					 * from the MATCHED to the NOT MATCHED cases.  If we are
+					 * already processing a NOT MATCHED BY SOURCE action, this
+					 * is not necessary.
 					 */
+					was_matched = relaction->mas_action->matchKind == MERGE_WHEN_MATCHED;
 					resultRelationDesc = resultRelInfo->ri_RelationDesc;
 					lockmode = ExecUpdateLockMode(estate, resultRelInfo);
 
-					inputslot = EvalPlanQualSlot(epqstate, resultRelationDesc,
-												 resultRelInfo->ri_RangeTableIndex);
+					if (was_matched)
+						inputslot = EvalPlanQualSlot(epqstate, resultRelationDesc,
+													 resultRelInfo->ri_RangeTableIndex);
+					else
+						inputslot = resultRelInfo->ri_oldTupleSlot;
 
 					result = table_tuple_lock(resultRelationDesc, tupleid,
 											  estate->es_snapshot,
@@ -3061,28 +3098,9 @@ lmerge_matched:
 					switch (result)
 					{
 						case TM_Ok:
-							epqslot = EvalPlanQual(epqstate,
-												   resultRelationDesc,
-												   resultRelInfo->ri_RangeTableIndex,
-												   inputslot);
-
-							/*
-							 * If we got no tuple, or the tuple we get has a
-							 * NULL ctid, go back to caller: this one is not a
-							 * MATCHED tuple anymore, so they can retry with
-							 * NOT MATCHED actions.
-							 */
-							if (TupIsNull(epqslot))
-								return false;
-
-							(void) ExecGetJunkAttribute(epqslot,
-														resultRelInfo->ri_RowIdAttNo,
-														&isNull);
-							if (isNull)
-								return false;
 
 							/*
-							 * When a tuple was updated and migrated to
+							 * If the tuple was updated and migrated to
 							 * another partition concurrently, the current
 							 * MERGE implementation can't follow.  There's
 							 * probably a better way to handle this case, but
@@ -3093,26 +3111,72 @@ lmerge_matched:
 							if (ItemPointerIndicatesMovedPartitions(&context->tmfd.ctid))
 								ereport(ERROR,
 										(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
-										 errmsg("tuple to be deleted was already moved to another partition due to concurrent update")));
+										 errmsg("tuple to be merged was already moved to another partition due to concurrent update")));
 
 							/*
-							 * A non-NULL ctid means that we are still dealing
-							 * with MATCHED case. Restart the loop so that we
-							 * apply all the MATCHED rules again, to ensure
-							 * that the first qualifying WHEN MATCHED action
-							 * is executed.
-							 *
-							 * Update tupleid to that of the new tuple, for
-							 * the refetch we do at the top.
+							 * If this was a MATCHED case, use EvalPlanQual()
+							 * to recheck the join condition.
+							 */
+							if (was_matched)
+							{
+								epqslot = EvalPlanQual(epqstate,
+													   resultRelationDesc,
+													   resultRelInfo->ri_RangeTableIndex,
+													   inputslot);
+
+								/*
+								 * If the subplan didn't return a tuple, then
+								 * we must be dealing with an inner join for
+								 * which the join condition no longer matches.
+								 * This can only happen if there are no NOT
+								 * MATCHED actions, and so there is nothing
+								 * more for us to do.
+								 */
+								if (TupIsNull(epqslot))
+									return true;
+
+								/*
+								 * If we got a NULL ctid from the subplan, the
+								 * join quals no longer pass and we switch to
+								 * the NOT MATCHED BY SOURCE case.
+								 */
+								(void) ExecGetJunkAttribute(epqslot,
+															resultRelInfo->ri_RowIdAttNo,
+															&isNull);
+								if (isNull)
+									epq_ok = false;
+
+								/*
+								 * Otherwise, recheck the join quals to see if
+								 * we need to switch to the NOT MATCHED BY
+								 * SOURCE case.
+								 */
+								if (!table_tuple_fetch_row_version(resultRelationDesc,
+																   &context->tmfd.ctid,
+																   SnapshotAny,
+																   resultRelInfo->ri_oldTupleSlot))
+									elog(ERROR, "failed to fetch the target tuple");
+
+								if (epq_ok)
+									epq_ok = ExecQual(resultRelInfo->ri_MergeJoinCondition,
+													  econtext);
+
+								/* Switch lists, if necessary */
+								if (!epq_ok)
+									actionStates = mergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE];
+							}
+
+							/*
+							 * Loop back and process the MATCHED or NOT
+							 * MATCHED BY SOURCE actions from the start.
 							 */
-							ItemPointerCopy(&context->tmfd.ctid, tupleid);
 							goto lmerge_matched;
 
 						case TM_Deleted:
 
 							/*
 							 * tuple already deleted; tell caller to run NOT
-							 * MATCHED actions
+							 * MATCHED [BY TARGET] actions
 							 */
 							return false;
 
@@ -3162,11 +3226,11 @@ lmerge_matched:
 	/*
 	 * Successfully executed an action or no qualifying action was found.
 	 */
-	return true;
+	return epq_ok;
 }
 
 /*
- * Execute the first qualifying NOT MATCHED action.
+ * Execute the first qualifying NOT MATCHED [BY TARGET] action.
  */
 static void
 ExecMergeNotMatched(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
@@ -3174,7 +3238,7 @@ ExecMergeNotMatched(ModifyTableContext *
 {
 	ModifyTableState *mtstate = context->mtstate;
 	ExprContext *econtext = mtstate->ps.ps_ExprContext;
-	List	   *actionStates = NIL;
+	List	   *actionStates;
 	ListCell   *l;
 
 	/*
@@ -3186,7 +3250,7 @@ ExecMergeNotMatched(ModifyTableContext *
 	 * XXX does this mean that we can avoid creating copies of actionStates on
 	 * partitioned tables, for not-matched actions?
 	 */
-	actionStates = resultRelInfo->ri_notMatchedMergeAction;
+	actionStates = resultRelInfo->ri_MergeActions[MERGE_WHEN_NOT_MATCHED_BY_TARGET];
 
 	/*
 	 * Make source tuple available to ExecQual and ExecProject. We don't need
@@ -3278,9 +3342,11 @@ ExecInitMerge(ModifyTableState *mtstate,
 	foreach(lc, node->mergeActionLists)
 	{
 		List	   *mergeActionList = lfirst(lc);
+		Node	   *joinCondition;
 		TupleDesc	relationDesc;
 		ListCell   *l;
 
+		joinCondition = (Node *) list_nth(node->mergeJoinConditions, i);
 		resultRelInfo = mtstate->resultRelInfo + i;
 		i++;
 		relationDesc = RelationGetDescr(resultRelInfo->ri_RelationDesc);
@@ -3289,13 +3355,16 @@ ExecInitMerge(ModifyTableState *mtstate,
 		if (unlikely(!resultRelInfo->ri_projectNewInfoValid))
 			ExecInitMergeTupleSlots(mtstate, resultRelInfo);
 
+		/* initialize state for join condition-checking */
+		resultRelInfo->ri_MergeJoinCondition =
+			ExecInitQual((List *) joinCondition, &mtstate->ps);
+
 		foreach(l, mergeActionList)
 		{
 			MergeAction *action = (MergeAction *) lfirst(l);
 			MergeActionState *action_state;
 			TupleTableSlot *tgtslot;
 			TupleDesc	tgtdesc;
-			List	  **list;
 
 			/*
 			 * Build action merge state for this rel.  (For partitions,
@@ -3307,15 +3376,12 @@ ExecInitMerge(ModifyTableState *mtstate,
 													  &mtstate->ps);
 
 			/*
-			 * We create two lists - one for WHEN MATCHED actions and one for
-			 * WHEN NOT MATCHED actions - and stick the MergeActionState into
-			 * the appropriate list.
+			 * We create three lists - one for each MergeMatchKind - and stick
+			 * the MergeActionState into the appropriate list.
 			 */
-			if (action_state->mas_action->matched)
-				list = &resultRelInfo->ri_matchedMergeAction;
-			else
-				list = &resultRelInfo->ri_notMatchedMergeAction;
-			*list = lappend(*list, action_state);
+			resultRelInfo->ri_MergeActions[action->matchKind] =
+				lappend(resultRelInfo->ri_MergeActions[action->matchKind],
+						action_state);
 
 			switch (action->commandType)
 			{
diff --git a/src/backend/nodes/nodeFuncs.c b/src/backend/nodes/nodeFuncs.c
new file mode 100644
index e1a5bc7..07da03e
--- a/src/backend/nodes/nodeFuncs.c
+++ b/src/backend/nodes/nodeFuncs.c
@@ -2584,6 +2584,8 @@ query_tree_walker_impl(Query *query,
 		return true;
 	if (WALK(query->mergeActionList))
 		return true;
+	if (WALK(query->mergeJoinCondition))
+		return true;
 	if (WALK(query->returningList))
 		return true;
 	if (WALK(query->jointree))
@@ -3608,6 +3610,7 @@ query_tree_mutator_impl(Query *query,
 	MUTATE(query->withCheckOptions, query->withCheckOptions, List *);
 	MUTATE(query->onConflict, query->onConflict, OnConflictExpr *);
 	MUTATE(query->mergeActionList, query->mergeActionList, List *);
+	MUTATE(query->mergeJoinCondition, query->mergeJoinCondition, Node *);
 	MUTATE(query->returningList, query->returningList, List *);
 	MUTATE(query->jointree, query->jointree, FromExpr *);
 	MUTATE(query->setOperations, query->setOperations, Node *);
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
new file mode 100644
index 610f4a5..1d36665
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -311,7 +311,8 @@ static ModifyTable *make_modifytable(Pla
 									 List *updateColnosLists,
 									 List *withCheckOptionLists, List *returningLists,
 									 List *rowMarks, OnConflictExpr *onconflict,
-									 List *mergeActionLists, int epqParam);
+									 List *mergeActionLists, List *mergeJoinConditions,
+									 int epqParam);
 static GatherMerge *create_gather_merge_plan(PlannerInfo *root,
 											 GatherMergePath *best_path);
 
@@ -2835,6 +2836,7 @@ create_modifytable_plan(PlannerInfo *roo
 							best_path->rowMarks,
 							best_path->onconflict,
 							best_path->mergeActionLists,
+							best_path->mergeJoinConditions,
 							best_path->epqParam);
 
 	copy_generic_path_info(&plan->plan, &best_path->path);
@@ -7014,7 +7016,8 @@ make_modifytable(PlannerInfo *root, Plan
 				 List *updateColnosLists,
 				 List *withCheckOptionLists, List *returningLists,
 				 List *rowMarks, OnConflictExpr *onconflict,
-				 List *mergeActionLists, int epqParam)
+				 List *mergeActionLists, List *mergeJoinConditions,
+				 int epqParam)
 {
 	ModifyTable *node = makeNode(ModifyTable);
 	List	   *fdw_private_list;
@@ -7084,6 +7087,7 @@ make_modifytable(PlannerInfo *root, Plan
 	node->returningLists = returningLists;
 	node->rowMarks = rowMarks;
 	node->mergeActionLists = mergeActionLists;
+	node->mergeJoinConditions = mergeJoinConditions;
 	node->epqParam = epqParam;
 
 	/*
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
new file mode 100644
index be4e182..04d24b1
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -912,6 +912,9 @@ subquery_planner(PlannerGlobal *glob, Qu
 								  EXPRKIND_QUAL);
 	}
 
+	parse->mergeJoinCondition =
+		preprocess_expression(root, parse->mergeJoinCondition, EXPRKIND_QUAL);
+
 	root->append_rel_list = (List *)
 		preprocess_expression(root, (Node *) root->append_rel_list,
 							  EXPRKIND_APPINFO);
@@ -1794,6 +1797,7 @@ grouping_planner(PlannerInfo *root, doub
 			List	   *withCheckOptionLists = NIL;
 			List	   *returningLists = NIL;
 			List	   *mergeActionLists = NIL;
+			List	   *mergeJoinConditions = NIL;
 			List	   *rowMarks;
 
 			if (bms_membership(root->all_result_relids) == BMS_MULTIPLE)
@@ -1900,6 +1904,19 @@ grouping_planner(PlannerInfo *root, doub
 						mergeActionLists = lappend(mergeActionLists,
 												   mergeActionList);
 					}
+					if (parse->commandType == CMD_MERGE)
+					{
+						Node	   *mergeJoinCondition = parse->mergeJoinCondition;
+
+						if (this_result_rel != top_result_rel)
+							mergeJoinCondition =
+								adjust_appendrel_attrs_multilevel(root,
+																  mergeJoinCondition,
+																  this_result_rel,
+																  top_result_rel);
+						mergeJoinConditions = lappend(mergeJoinConditions,
+													  mergeJoinCondition);
+					}
 				}
 
 				if (resultRelations == NIL)
@@ -1924,6 +1941,8 @@ grouping_planner(PlannerInfo *root, doub
 						returningLists = list_make1(parse->returningList);
 					if (parse->mergeActionList)
 						mergeActionLists = list_make1(parse->mergeActionList);
+					if (parse->commandType == CMD_MERGE)
+						mergeJoinConditions = list_make1(parse->mergeJoinCondition);
 				}
 			}
 			else
@@ -1939,6 +1958,8 @@ grouping_planner(PlannerInfo *root, doub
 					returningLists = list_make1(parse->returningList);
 				if (parse->mergeActionList)
 					mergeActionLists = list_make1(parse->mergeActionList);
+				if (parse->commandType == CMD_MERGE)
+					mergeJoinConditions = list_make1(parse->mergeJoinCondition);
 			}
 
 			/*
@@ -1966,6 +1987,7 @@ grouping_planner(PlannerInfo *root, doub
 										rowMarks,
 										parse->onConflict,
 										mergeActionLists,
+										mergeJoinConditions,
 										assign_special_exec_param(root));
 		}
 
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
new file mode 100644
index 22a1fa2..ceb3260
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -1144,7 +1144,9 @@ set_plan_refs(PlannerInfo *root, Plan *p
 				 */
 				if (splan->mergeActionLists != NIL)
 				{
+					List	   *newMJC = NIL;
 					ListCell   *lca,
+							   *lcj,
 							   *lcr;
 
 					/*
@@ -1165,10 +1167,12 @@ set_plan_refs(PlannerInfo *root, Plan *p
 
 					itlist = build_tlist_index(subplan->targetlist);
 
-					forboth(lca, splan->mergeActionLists,
-							lcr, splan->resultRelations)
+					forthree(lca, splan->mergeActionLists,
+							 lcj, splan->mergeJoinConditions,
+							 lcr, splan->resultRelations)
 					{
 						List	   *mergeActionList = lfirst(lca);
+						Node	   *mergeJoinCondition = lfirst(lcj);
 						Index		resultrel = lfirst_int(lcr);
 
 						foreach(l, mergeActionList)
@@ -1193,7 +1197,19 @@ set_plan_refs(PlannerInfo *root, Plan *p
 																  NRM_EQUAL,
 																  NUM_EXEC_QUAL(plan));
 						}
+
+						/* Fix join condition too. */
+						mergeJoinCondition = (Node *)
+							fix_join_expr(root,
+										  (List *) mergeJoinCondition,
+										  NULL, itlist,
+										  resultrel,
+										  rtoffset,
+										  NRM_EQUAL,
+										  NUM_EXEC_QUAL(plan));
+						newMJC = lappend(newMJC, mergeJoinCondition);
 					}
+					splan->mergeJoinConditions = newMJC;
 				}
 
 				splan->nominalRelation += rtoffset;
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
new file mode 100644
index 300691c..2d8956d
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -153,9 +153,11 @@ transform_MERGE_to_join(Query *parse)
 {
 	RangeTblEntry *joinrte;
 	JoinExpr   *joinexpr;
+	bool		have_action[3];
 	JoinType	jointype;
 	int			joinrti;
 	List	   *vars;
+	RangeTblRef *rtr;
 
 	if (parse->commandType != CMD_MERGE)
 		return;
@@ -164,11 +166,27 @@ transform_MERGE_to_join(Query *parse)
 	vars = NIL;
 
 	/*
-	 * When any WHEN NOT MATCHED THEN INSERT clauses exist, we need to use an
-	 * outer join so that we process all unmatched tuples from the source
-	 * relation.  If none exist, we can use an inner join.
+	 * Work out what kind of join is required.  If there any WHEN NOT MATCHED
+	 * BY SOURCE/TARGET actions, an outer join is required so that we process
+	 * all unmatched tuples from the source and/or target relations.
+	 * Otherwise, we can use an inner join.
 	 */
-	if (parse->mergeUseOuterJoin)
+	have_action[MERGE_WHEN_MATCHED] = false;
+	have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	have_action[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
+
+	foreach_node(MergeAction, action, parse->mergeActionList)
+	{
+		if (action->commandType != CMD_NOTHING)
+			have_action[action->matchKind] = true;
+	}
+
+	if (have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] &&
+		have_action[MERGE_WHEN_NOT_MATCHED_BY_TARGET])
+		jointype = JOIN_FULL;
+	else if (have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE])
+		jointype = JOIN_LEFT;
+	else if (have_action[MERGE_WHEN_NOT_MATCHED_BY_TARGET])
 		jointype = JOIN_RIGHT;
 	else
 		jointype = JOIN_INNER;
@@ -204,16 +222,16 @@ transform_MERGE_to_join(Query *parse)
 	 * trigger-updatable view, it will be the expanded view subquery that we
 	 * need to pull data from.
 	 */
+	rtr = makeNode(RangeTblRef);
+	rtr->rtindex = parse->mergeTargetRelation;
 	joinexpr = makeNode(JoinExpr);
 	joinexpr->jointype = jointype;
 	joinexpr->isNatural = false;
-	joinexpr->larg = (Node *) makeNode(RangeTblRef);
-	((RangeTblRef *) joinexpr->larg)->rtindex = parse->mergeTargetRelation;
-	joinexpr->rarg = linitial(parse->jointree->fromlist);	/* original join */
+	joinexpr->larg = (Node *) makeFromExpr(list_make1(rtr), parse->jointree->quals);
+	joinexpr->rarg = linitial(parse->jointree->fromlist);	/* source rel */
 	joinexpr->usingClause = NIL;
 	joinexpr->join_using_alias = NULL;
-	/* The quals are removed from the jointree and into this specific join */
-	joinexpr->quals = parse->jointree->quals;
+	joinexpr->quals = parse->mergeJoinCondition;
 	joinexpr->alias = NULL;
 	joinexpr->rtindex = joinrti;
 
@@ -233,6 +251,15 @@ transform_MERGE_to_join(Query *parse)
 			add_nulling_relids((Node *) parse->targetList,
 							   bms_make_singleton(parse->mergeTargetRelation),
 							   bms_make_singleton(joinrti));
+
+	/*
+	 * If there are any WHEN NOT MATCHED BY SOURCE actions, the executor will
+	 * use the join condition to distinguish between MATCHED and NOT MATCHED
+	 * BY SOURCE cases.  Otherwise, it's no longer needed, and we set it to
+	 * NULL, saving cycles during planning and execution.
+	 */
+	if (!have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE])
+		parse->mergeJoinCondition = NULL;
 }
 
 /*
@@ -2173,6 +2200,8 @@ perform_pullup_replace_vars(PlannerInfo
 				pullup_replace_vars((Node *) action->targetList, rvcontext);
 		}
 	}
+	parse->mergeJoinCondition = pullup_replace_vars(parse->mergeJoinCondition,
+													rvcontext);
 	replace_vars_in_jointree((Node *) parse->jointree, rvcontext);
 	Assert(parse->setOperations == NULL);
 	parse->havingQual = pullup_replace_vars(parse->havingQual, rvcontext);
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
new file mode 100644
index 7698bfa..931b9c0
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -134,6 +134,7 @@ preprocess_targetlist(PlannerInfo *root)
 	if (command_type == CMD_MERGE)
 	{
 		ListCell   *l;
+		List	   *vars;
 
 		/*
 		 * For MERGE, handle targetlist of each MergeAction separately. Give
@@ -144,7 +145,6 @@ preprocess_targetlist(PlannerInfo *root)
 		foreach(l, parse->mergeActionList)
 		{
 			MergeAction *action = (MergeAction *) lfirst(l);
-			List	   *vars;
 			ListCell   *l2;
 
 			if (action->commandType == CMD_INSERT)
@@ -182,6 +182,30 @@ preprocess_targetlist(PlannerInfo *root)
 			}
 			list_free(vars);
 		}
+
+		/*
+		 * Add resjunk entries for any Vars and PlaceHolderVars used in the
+		 * join condition that belong to relations other than the target.  We
+		 * don't expect to see any aggregates or window functions here.
+		 */
+		vars = pull_var_clause(parse->mergeJoinCondition,
+							   PVC_INCLUDE_PLACEHOLDERS);
+		foreach(l, vars)
+		{
+			Var		   *var = (Var *) lfirst(l);
+			TargetEntry *tle;
+
+			if (IsA(var, Var) && var->varno == result_relation)
+				continue;		/* don't need it */
+
+			if (tlist_member((Expr *) var, tlist))
+				continue;		/* already got it */
+
+			tle = makeTargetEntry((Expr *) var,
+								  list_length(tlist) + 1,
+								  NULL, true);
+			tlist = lappend(tlist, tle);
+		}
 	}
 
 	/*
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
new file mode 100644
index 6f79b2e..8635b24
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -3706,6 +3706,7 @@ create_lockrows_path(PlannerInfo *root,
  * 'onconflict' is the ON CONFLICT clause, or NULL
  * 'epqParam' is the ID of Param for EvalPlanQual re-eval
  * 'mergeActionLists' is a list of lists of MERGE actions (one per rel)
+ * 'mergeJoinConditions' is a list of join conditions for MERGE (one per rel)
  */
 ModifyTablePath *
 create_modifytable_path(PlannerInfo *root, RelOptInfo *rel,
@@ -3717,7 +3718,8 @@ create_modifytable_path(PlannerInfo *roo
 						List *updateColnosLists,
 						List *withCheckOptionLists, List *returningLists,
 						List *rowMarks, OnConflictExpr *onconflict,
-						List *mergeActionLists, int epqParam)
+						List *mergeActionLists, List *mergeJoinConditions,
+						int epqParam)
 {
 	ModifyTablePath *pathnode = makeNode(ModifyTablePath);
 
@@ -3785,6 +3787,7 @@ create_modifytable_path(PlannerInfo *roo
 	pathnode->onconflict = onconflict;
 	pathnode->epqParam = epqParam;
 	pathnode->mergeActionLists = mergeActionLists;
+	pathnode->mergeJoinConditions = mergeJoinConditions;
 
 	return pathnode;
 }
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index 130f7fc..f6b4c80
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -275,6 +275,7 @@ static Node *makeRecursiveViewSelect(cha
 	struct SelectLimit *selectlimit;
 	SetQuantifier setquantifier;
 	struct GroupClause *groupclause;
+	MergeMatchKind mergematch;
 	MergeWhenClause *mergewhen;
 	struct KeyActions *keyactions;
 	struct KeyAction *keyaction;
@@ -515,6 +516,7 @@ static Node *makeRecursiveViewSelect(cha
 %type <onconflict> opt_on_conflict
 %type <mergewhen>	merge_insert merge_update merge_delete
 
+%type <mergematch> merge_when_tgt_matched merge_when_tgt_not_matched
 %type <node>	merge_when_clause opt_merge_when_condition
 %type <list>	merge_when_list
 
@@ -759,11 +761,11 @@ static Node *makeRecursiveViewSelect(cha
 	SAVEPOINT SCALAR SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT
 	SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
-	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
+	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SOURCE SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRIP_P
 	SUBSCRIPTION SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
 
-	TABLE TABLES TABLESAMPLE TABLESPACE TEMP TEMPLATE TEMPORARY TEXT_P THEN
+	TABLE TABLES TABLESAMPLE TABLESPACE TARGET TEMP TEMPLATE TEMPORARY TEXT_P THEN
 	TIES TIME TIMESTAMP TO TRAILING TRANSACTION TRANSFORM
 	TREAT TRIGGER TRIM TRUE_P
 	TRUNCATE TRUSTED TYPE_P TYPES_P
@@ -12386,50 +12388,66 @@ merge_when_list:
 			| merge_when_list merge_when_clause		{ $$ = lappend($1,$2); }
 		;
 
+/*
+ * A WHEN clause may be WHEN MATCHED, WHEN NOT MATCHED BY SOURCE, or WHEN NOT
+ * MATCHED [BY TARGET]. The first two cases match target tuples, and support
+ * UPDATE/DELETE/DO NOTHING actions. The third case does not match target
+ * tuples, and only supports INSERT/DO NOTHING actions.
+ */
 merge_when_clause:
-			WHEN MATCHED opt_merge_when_condition THEN merge_update
+			merge_when_tgt_matched opt_merge_when_condition THEN merge_update
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN merge_delete
+			| merge_when_tgt_matched opt_merge_when_condition THEN merge_delete
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN merge_insert
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN merge_insert
 				{
-					$6->matched = false;
-					$6->condition = $4;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $6;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = true;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $3;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = false;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $4;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
 		;
 
+merge_when_tgt_matched:
+			WHEN MATCHED					{ $$ = MERGE_WHEN_MATCHED; }
+			| WHEN NOT MATCHED BY SOURCE	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_SOURCE; }
+		;
+
+merge_when_tgt_not_matched:
+			WHEN NOT MATCHED				{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+			| WHEN NOT MATCHED BY TARGET	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+		;
+
 opt_merge_when_condition:
 			AND a_expr				{ $$ = $2; }
 			|						{ $$ = NULL; }
@@ -17388,6 +17406,7 @@ unreserved_keyword:
 			| SIMPLE
 			| SKIP
 			| SNAPSHOT
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -17406,6 +17425,7 @@ unreserved_keyword:
 			| SYSTEM_P
 			| TABLES
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
@@ -18001,6 +18021,7 @@ bare_label_keyword:
 			| SMALLINT
 			| SNAPSHOT
 			| SOME
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -18024,6 +18045,7 @@ bare_label_keyword:
 			| TABLES
 			| TABLESAMPLE
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
diff --git a/src/backend/parser/parse_merge.c b/src/backend/parser/parse_merge.c
new file mode 100644
index 4356d61..f03d7c0
--- a/src/backend/parser/parse_merge.c
+++ b/src/backend/parser/parse_merge.c
@@ -43,9 +43,9 @@ static void setNamespaceVisibilityForRTE
  * Make appropriate changes to the namespace visibility while transforming
  * individual action's quals and targetlist expressions. In particular, for
  * INSERT actions we must only see the source relation (since INSERT action is
- * invoked for NOT MATCHED tuples and hence there is no target tuple to deal
- * with). On the other hand, UPDATE and DELETE actions can see both source and
- * target relations.
+ * invoked for NOT MATCHED [BY TARGET] tuples and hence there is no target
+ * tuple to deal with). On the other hand, UPDATE and DELETE actions can see
+ * both source and target relations, unless invoked for NOT MATCHED BY SOURCE.
  *
  * Also, since the internal join node can hide the source and target
  * relations, we must explicitly make the respective relation as visible so
@@ -61,7 +61,7 @@ setNamespaceForMergeWhen(ParseState *pst
 	targetRelRTE = rt_fetch(targetRTI, pstate->p_rtable);
 	sourceRelRTE = rt_fetch(sourceRTI, pstate->p_rtable);
 
-	if (mergeWhenClause->matched)
+	if (mergeWhenClause->matchKind == MERGE_WHEN_MATCHED)
 	{
 		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
 			   mergeWhenClause->commandType == CMD_DELETE ||
@@ -73,11 +73,25 @@ setNamespaceForMergeWhen(ParseState *pst
 		setNamespaceVisibilityForRTE(pstate->p_namespace,
 									 sourceRelRTE, true, true);
 	}
-	else
+	else if (mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
 	{
 		/*
-		 * NOT MATCHED actions can't see target relation, but they can see
-		 * source relation.
+		 * NOT MATCHED BY SOURCE actions can see the target relation, but they
+		 * can't see the source relation.
+		 */
+		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
+			   mergeWhenClause->commandType == CMD_DELETE ||
+			   mergeWhenClause->commandType == CMD_NOTHING);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 targetRelRTE, true, true);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 sourceRelRTE, false, false);
+	}
+	else						/* MERGE_WHEN_NOT_MATCHED_BY_TARGET */
+	{
+		/*
+		 * NOT MATCHED [BY TARGET] actions can't see target relation, but they
+		 * can see source relation.
 		 */
 		Assert(mergeWhenClause->commandType == CMD_INSERT ||
 			   mergeWhenClause->commandType == CMD_NOTHING);
@@ -98,10 +112,9 @@ transformMergeStmt(ParseState *pstate, M
 	Query	   *qry = makeNode(Query);
 	ListCell   *l;
 	AclMode		targetPerms = ACL_NO_RIGHTS;
-	bool		is_terminal[2];
+	bool		is_terminal[3];
 	Index		sourceRTI;
 	List	   *mergeActionList;
-	Node	   *joinExpr;
 	ParseNamespaceItem *nsitem;
 
 	/* There can't be any outer WITH to worry about */
@@ -125,12 +138,12 @@ transformMergeStmt(ParseState *pstate, M
 	/*
 	 * Check WHEN clauses for permissions and sanity
 	 */
-	is_terminal[0] = false;
-	is_terminal[1] = false;
+	is_terminal[MERGE_WHEN_MATCHED] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
 	foreach(l, stmt->mergeWhenClauses)
 	{
 		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
-		int			when_type = (mergeWhenClause->matched ? 0 : 1);
 
 		/*
 		 * Collect permissions to check, according to action types. We require
@@ -160,12 +173,12 @@ transformMergeStmt(ParseState *pstate, M
 		/*
 		 * Check for unreachable WHEN clauses
 		 */
-		if (is_terminal[when_type])
+		if (is_terminal[mergeWhenClause->matchKind])
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
 					 errmsg("unreachable WHEN clause specified after unconditional WHEN clause")));
 		if (mergeWhenClause->condition == NULL)
-			is_terminal[when_type] = true;
+			is_terminal[mergeWhenClause->matchKind] = true;
 	}
 
 	/*
@@ -226,16 +239,15 @@ transformMergeStmt(ParseState *pstate, M
 	 * side, so add that to the namespace.
 	 */
 	addNSItemToQuery(pstate, pstate->p_target_nsitem, false, true, true);
-	joinExpr = transformExpr(pstate, stmt->joinCondition,
-							 EXPR_KIND_JOIN_ON);
+	qry->mergeJoinCondition = transformExpr(pstate, stmt->joinCondition,
+											EXPR_KIND_JOIN_ON);
 
 	/*
 	 * Create the temporary query's jointree using the joinlist we built using
-	 * just the source relation; the target relation is not included.  The
-	 * quals we use are the join conditions to the merge target.  The join
+	 * just the source relation; the target relation is not included. The join
 	 * will be constructed fully by transform_MERGE_to_join.
 	 */
-	qry->jointree = makeFromExpr(pstate->p_joinlist, joinExpr);
+	qry->jointree = makeFromExpr(pstate->p_joinlist, NULL);
 
 	/*
 	 * We now have a good query shape, so now look at the WHEN conditions and
@@ -259,11 +271,7 @@ transformMergeStmt(ParseState *pstate, M
 
 		action = makeNode(MergeAction);
 		action->commandType = mergeWhenClause->commandType;
-		action->matched = mergeWhenClause->matched;
-
-		/* Use an outer join if any INSERT actions exist in the command. */
-		if (action->commandType == CMD_INSERT)
-			qry->mergeUseOuterJoin = true;
+		action->matchKind = mergeWhenClause->matchKind;
 
 		/*
 		 * Set namespace for the specific action. This must be done before
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
new file mode 100644
index a928a8c..648470b
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -7091,6 +7091,7 @@ get_merge_query_def(Query *query, depars
 	StringInfo	buf = context->buf;
 	RangeTblEntry *rte;
 	ListCell   *lc;
+	bool		haveNotMatchedBySource;
 
 	/* Insert the WITH clause if given */
 	get_with_clause(query, context);
@@ -7116,7 +7117,26 @@ get_merge_query_def(Query *query, depars
 	get_from_clause(query, " USING ", context);
 	appendContextKeyword(context, " ON ",
 						 -PRETTYINDENT_STD, PRETTYINDENT_STD, 2);
-	get_rule_expr(query->jointree->quals, context, false);
+	get_rule_expr(query->mergeJoinCondition, context, false);
+
+	/*
+	 * Test for any NOT MATCHED BY SOURCE actions.  If there are none, then
+	 * any NOT MATCHED BY TARGET actions are output as "WHEN NOT MATCHED", per
+	 * SQL standard.  Otherwise, we have a non-SQL-standard query, so output
+	 * "BY SOURCE" / "BY TARGET" qualifiers for all NOT MATCHED actions, to be
+	 * more explicit.
+	 */
+	haveNotMatchedBySource = false;
+	foreach(lc, query->mergeActionList)
+	{
+		MergeAction *action = lfirst_node(MergeAction, lc);
+
+		if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+		{
+			haveNotMatchedBySource = true;
+			break;
+		}
+	}
 
 	/* Print each merge action */
 	foreach(lc, query->mergeActionList)
@@ -7125,7 +7145,24 @@ get_merge_query_def(Query *query, depars
 
 		appendContextKeyword(context, " WHEN ",
 							 -PRETTYINDENT_STD, PRETTYINDENT_STD, 2);
-		appendStringInfo(buf, "%sMATCHED", action->matched ? "" : "NOT ");
+		switch (action->matchKind)
+		{
+			case MERGE_WHEN_MATCHED:
+				appendStringInfo(buf, "MATCHED");
+				break;
+			case MERGE_WHEN_NOT_MATCHED_BY_SOURCE:
+				appendStringInfo(buf, "NOT MATCHED BY SOURCE");
+				break;
+			case MERGE_WHEN_NOT_MATCHED_BY_TARGET:
+				if (haveNotMatchedBySource)
+					appendStringInfo(buf, "NOT MATCHED BY TARGET");
+				else
+					appendStringInfo(buf, "NOT MATCHED");
+				break;
+			default:
+				elog(ERROR, "unrecognized matchKind: %d",
+					 (int) action->matchKind);
+		}
 
 		if (action->qual)
 		{
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
new file mode 100644
index aa1acf8..b887c46
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -4332,17 +4332,35 @@ psql_completion(const char *text, int st
 			 TailMatches("USING", MatchAny, MatchAny, "ON", MatchAny, MatchAny, MatchAny, "WHEN"))
 		COMPLETE_WITH("MATCHED", "NOT MATCHED");
 
-	/* Complete ... WHEN [NOT] MATCHED with THEN/AND */
+	/*
+	 * Complete ... WHEN MATCHED and WHEN NOT MATCHED BY SOURCE|TARGET with
+	 * THEN/AND
+	 */
 	else if (TailMatches("WHEN", "MATCHED") ||
-			 TailMatches("WHEN", "NOT", "MATCHED"))
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE|TARGET"))
 		COMPLETE_WITH("THEN", "AND");
 
-	/* Complete ... WHEN MATCHED THEN with UPDATE SET/DELETE/DO NOTHING */
-	else if (TailMatches("WHEN", "MATCHED", "THEN"))
+	/* Complete ... WHEN NOT MATCHED with BY/THEN/AND */
+	else if (TailMatches("WHEN", "NOT", "MATCHED"))
+		COMPLETE_WITH("BY", "THEN", "AND");
+
+	/* Complete ... WHEN NOT MATCHED BY with SOURCE/TARGET */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "BY"))
+		COMPLETE_WITH("SOURCE", "TARGET");
+
+	/*
+	 * Complete ... WHEN MATCHED THEN and WHEN NOT MATCHED BY SOURCE THEN with
+	 * UPDATE SET/DELETE/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE", "THEN"))
 		COMPLETE_WITH("UPDATE SET", "DELETE", "DO NOTHING");
 
-	/* Complete ... WHEN NOT MATCHED THEN with INSERT/DO NOTHING */
-	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN"))
+	/*
+	 * Complete ... WHEN NOT MATCHED [BY TARGET] THEN with INSERT/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "TARGET", "THEN"))
 		COMPLETE_WITH("INSERT", "DO NOTHING");
 
 /* NOTIFY --- can be inside EXPLAIN, RULE, etc */
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
new file mode 100644
index 444a5f0..9f65cfb
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -544,9 +544,11 @@ typedef struct ResultRelInfo
 	/* ON CONFLICT evaluation state */
 	OnConflictSetState *ri_onConflict;
 
-	/* for MERGE, lists of MergeActionState */
-	List	   *ri_matchedMergeAction;
-	List	   *ri_notMatchedMergeAction;
+	/* for MERGE, lists of MergeActionState (one per MergeMatchKind) */
+	List	   *ri_MergeActions[3];
+
+	/* for MERGE, join condition-checking expr state */
+	ExprState  *ri_MergeJoinCondition;
 
 	/* partition check expression state (NULL if not set up yet) */
 	ExprState  *ri_PartitionCheckExpr;
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
new file mode 100644
index d60e148..b994224
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -175,8 +175,6 @@ typedef struct Query
 								 * also USING clause for MERGE */
 
 	List	   *mergeActionList;	/* list of actions for MERGE (only) */
-	/* whether to use outer join */
-	bool		mergeUseOuterJoin pg_node_attr(query_jumble_ignore);
 
 	/*
 	 * rtable index of target relation for MERGE to pull data. Initially, this
@@ -186,6 +184,9 @@ typedef struct Query
 	 */
 	int			mergeTargetRelation pg_node_attr(query_jumble_ignore);
 
+	/* join condition between source and target for MERGE */
+	Node	   *mergeJoinCondition;
+
 	List	   *targetList;		/* target list (of TargetEntry) */
 
 	/* OVERRIDING clause */
@@ -1673,7 +1674,7 @@ typedef struct CommonTableExpr
 typedef struct MergeWhenClause
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *condition;		/* WHEN conditions (raw parser) */
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
new file mode 100644
index 534692b..5ccfa5f
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -2367,6 +2367,8 @@ typedef struct ModifyTablePath
 	int			epqParam;		/* ID of Param for EvalPlanQual re-eval */
 	List	   *mergeActionLists;	/* per-target-table lists of actions for
 									 * MERGE */
+	List	   *mergeJoinConditions;	/* per-target-table join conditions
+										 * for MERGE */
 } ModifyTablePath;
 
 /*
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
new file mode 100644
index b4ef6bc..ebefd65
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -251,6 +251,8 @@ typedef struct ModifyTable
 	List	   *exclRelTlist;	/* tlist of the EXCLUDED pseudo relation */
 	List	   *mergeActionLists;	/* per-target-table lists of actions for
 									 * MERGE */
+	List	   *mergeJoinConditions;	/* per-target-table join conditions
+										 * for MERGE */
 } ModifyTable;
 
 struct PartitionPruneInfo;		/* forward reference to struct below */
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
new file mode 100644
index 4a15460..f7eebd8
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -1732,10 +1732,18 @@ typedef struct BooleanTest
  *
  * Transformed representation of a WHEN clause in a MERGE statement
  */
+
+typedef enum MergeMatchKind
+{
+	MERGE_WHEN_MATCHED,
+	MERGE_WHEN_NOT_MATCHED_BY_SOURCE,
+	MERGE_WHEN_NOT_MATCHED_BY_TARGET
+} MergeMatchKind;
+
 typedef struct MergeAction
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	/* OVERRIDING clause */
 	OverridingKind override pg_node_attr(query_jumble_ignore);
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
new file mode 100644
index c43d97b..1b3dd52
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -283,7 +283,8 @@ extern ModifyTablePath *create_modifytab
 												List *updateColnosLists,
 												List *withCheckOptionLists, List *returningLists,
 												List *rowMarks, OnConflictExpr *onconflict,
-												List *mergeActionLists, int epqParam);
+												List *mergeActionLists, List *mergeJoinConditions,
+												int epqParam);
 extern LimitPath *create_limit_path(PlannerInfo *root, RelOptInfo *rel,
 									Path *subpath,
 									Node *limitOffset, Node *limitCount,
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
new file mode 100644
index 2331aca..b7d5515
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -403,6 +403,7 @@ PG_KEYWORD("skip", SKIP, UNRESERVED_KEYW
 PG_KEYWORD("smallint", SMALLINT, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("snapshot", SNAPSHOT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("some", SOME, RESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("source", SOURCE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("sql", SQL_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("stable", STABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("standalone", STANDALONE_P, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -426,6 +427,7 @@ PG_KEYWORD("table", TABLE, RESERVED_KEYW
 PG_KEYWORD("tables", TABLES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablesample", TABLESAMPLE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablespace", TABLESPACE, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("target", TARGET, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temp", TEMP, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("template", TEMPLATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temporary", TEMPORARY, UNRESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/test/isolation/expected/merge-update.out b/src/test/isolation/expected/merge-update.out
new file mode 100644
index 55b1f90..11328aa
--- a/src/test/isolation/expected/merge-update.out
+++ b/src/test/isolation/expected/merge-update.out
@@ -37,13 +37,15 @@ step merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a';
 
 step select2: SELECT * FROM target;
-key|val                     
----+------------------------
-  2|setup1 updated by merge1
-  1|merge2a                 
+key|val                                                   
+---+------------------------------------------------------
+  3|setup1 updated by merge1 source not matched by merge2a
+  1|merge2a                                               
 (2 rows)
 
 step c2: COMMIT;
@@ -65,15 +67,17 @@ step merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a';
  <waiting ...>
 step c1: COMMIT;
 step merge2a: <... completed>
 step select2: SELECT * FROM target;
-key|val                     
----+------------------------
-  2|setup1 updated by merge1
-  1|merge2a                 
+key|val                                                   
+---+------------------------------------------------------
+  3|setup1 updated by merge1 source not matched by merge2a
+  1|merge2a                                               
 (2 rows)
 
 step c2: COMMIT;
@@ -95,7 +99,9 @@ step merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a';
  <waiting ...>
 step a1: ABORT;
 step merge2a: <... completed>
@@ -184,15 +190,17 @@ step pa_merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a';
  <waiting ...>
 step c1: COMMIT;
 step pa_merge2a: <... completed>
 step pa_select2: SELECT * FROM pa_target;
 key|val                                               
 ---+--------------------------------------------------
-  2|initial                                           
   2|initial updated by pa_merge1 updated by pa_merge2a
+  3|initial source not matched by pa_merge2a          
 (2 rows)
 
 step c2: COMMIT;
@@ -214,7 +222,9 @@ step pa_merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a';
  <waiting ...>
 step c1: COMMIT;
 step pa_merge2a: <... completed>
@@ -241,14 +251,16 @@ step pa_merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a';
 
 step pa_select2: SELECT * FROM pa_target;
-key|val                         
----+----------------------------
-  1|pa_merge2a                  
-  2|initial                     
-  2|initial updated by pa_merge2
+key|val                                                          
+---+-------------------------------------------------------------
+  1|pa_merge2a                                                   
+  3|initial source not matched by pa_merge2a                     
+  3|initial updated by pa_merge2 source not matched by pa_merge2a
 (3 rows)
 
 step c2: COMMIT;
diff --git a/src/test/isolation/specs/merge-update.spec b/src/test/isolation/specs/merge-update.spec
new file mode 100644
index e8d0166..04f5243
--- a/src/test/isolation/specs/merge-update.spec
+++ b/src/test/isolation/specs/merge-update.spec
@@ -91,7 +91,9 @@ step "merge2a"
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a';
 }
 step "merge2b"
 {
@@ -121,7 +123,9 @@ step "pa_merge2a"
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a';
 }
 # MERGE proceeds only if 'val' unchanged
 step "pa_merge2b_when"
diff --git a/src/test/regress/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index e3ebf46..17c0cba
--- a/src/test/regress/expected/merge.out
+++ b/src/test/regress/expected/merge.out
@@ -72,6 +72,15 @@ WHEN MATCHED THEN
 ERROR:  syntax error at or near "INSERT"
 LINE 5:  INSERT DEFAULT VALUES;
          ^
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
+ERROR:  syntax error at or near "INSERT"
+LINE 5:  INSERT DEFAULT VALUES;
+         ^
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -108,6 +117,15 @@ WHEN NOT MATCHED THEN
 ERROR:  syntax error at or near "UPDATE"
 LINE 5:  UPDATE SET balance = 0;
          ^
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
+ERROR:  syntax error at or near "UPDATE"
+LINE 5:  UPDATE SET balance = 0;
+         ^
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -270,6 +288,22 @@ SELECT * FROM target ORDER BY tid;
 (4 rows)
 
 ROLLBACK;
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   4 |      40
+(1 row)
+
+ROLLBACK;
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -737,6 +771,19 @@ SELECT * FROM wq_target;
    1 |      -1
 (1 row)
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+ERROR:  invalid reference to FROM-clause entry for table "s"
+LINE 3: WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+                                       ^
+DETAIL:  There is an entry for table "s", but it cannot be referenced from this part of the query.
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
  balance | sid 
@@ -922,6 +969,45 @@ SELECT * FROM target ORDER BY tid;
 (3 rows)
 
 ROLLBACK;
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE DELETE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  BEFORE INSERT ROW trigger row: (4,40)
+NOTICE:  BEFORE DELETE ROW trigger row: (2,20)
+NOTICE:  BEFORE UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  AFTER INSERT ROW trigger row: (4,40)
+NOTICE:  AFTER DELETE ROW trigger row: (2,20)
+NOTICE:  AFTER UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER DELETE STATEMENT trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |       0
+   3 |      10
+   4 |      40
+(3 rows)
+
+ROLLBACK;
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -1450,6 +1536,50 @@ WHEN NOT MATCHED AND s.a < 20 THEN
                ->  Seq Scan on ex_mtarget t (actual rows=49 loops=1)
 (12 rows)
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=54
+   ->  Merge Left Join (actual rows=54 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=100
+   ->  Merge Full Join (actual rows=100 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
@@ -1529,7 +1659,7 @@ CREATE TABLE pa_source (sid integer, del
 -- insert many rows to the source table
 INSERT INTO pa_source SELECT id, id * 10  FROM generate_series(1,14) AS id;
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 -- try simple MERGE
 BEGIN;
 MERGE INTO pa_target t
@@ -1538,10 +1668,12 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
    3 |     330 | initial updated by merge
@@ -1556,7 +1688,8 @@ SELECT * FROM pa_target ORDER BY tid;
   12 |     120 | inserted by merge
   13 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+  15 |    1500 | initial not matched by source
+(15 rows)
 
 ROLLBACK;
 -- same with a constant qual
@@ -1567,31 +1700,34 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
+   3 |     300 | initial not matched by source
    3 |      30 | inserted by merge
-   3 |     300 | initial
    4 |      40 | inserted by merge
-   5 |     500 | initial
+   5 |     500 | initial not matched by source
    5 |      50 | inserted by merge
    6 |      60 | inserted by merge
-   7 |     700 | initial
+   7 |     700 | initial not matched by source
    7 |      70 | inserted by merge
    8 |      80 | inserted by merge
+   9 |     900 | initial not matched by source
    9 |      90 | inserted by merge
-   9 |     900 | initial
   10 |     100 | inserted by merge
-  11 |    1100 | initial
+  11 |    1100 | initial not matched by source
   11 |     110 | inserted by merge
   12 |     120 | inserted by merge
-  13 |    1300 | initial
+  13 |    1300 | initial not matched by source
   13 |     130 | inserted by merge
   14 |     140 | inserted by merge
-(20 rows)
+  15 |    1500 | initial not matched by source
+(21 rows)
 
 ROLLBACK;
 -- try updating the partition key column
@@ -1606,7 +1742,9 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 IF FOUND THEN
   GET DIAGNOSTICS result := ROW_COUNT;
 END IF;
@@ -1616,27 +1754,28 @@ $$;
 SELECT merge_func();
  merge_func 
 ------------
-         14
+         15
 (1 row)
 
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
+   1 |    1500 | initial not matched by source
    2 |     110 | initial updated by merge
    2 |      20 | inserted by merge
-   4 |      40 | inserted by merge
    4 |     330 | initial updated by merge
+   4 |      40 | inserted by merge
    6 |     550 | initial updated by merge
    6 |      60 | inserted by merge
-   8 |      80 | inserted by merge
    8 |     770 | initial updated by merge
+   8 |      80 | inserted by merge
   10 |     990 | initial updated by merge
   10 |     100 | inserted by merge
   12 |    1210 | initial updated by merge
   12 |     120 | inserted by merge
   14 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+(15 rows)
 
 ROLLBACK;
 DROP TABLE pa_target CASCADE;
@@ -1658,7 +1797,7 @@ ALTER TABLE pa_target ATTACH PARTITION p
 ALTER TABLE pa_target ATTACH PARTITION part3 FOR VALUES IN (3,8,9);
 ALTER TABLE pa_target ATTACH PARTITION part4 DEFAULT;
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 -- try simple MERGE
 BEGIN;
 DO $$
@@ -1671,15 +1810,17 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 14
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 15
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
    3 |     330 | initial updated by merge
@@ -1694,7 +1835,8 @@ SELECT * FROM pa_target ORDER BY tid;
   12 |     120 | inserted by merge
   13 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+  15 |    1500 | initial not matched by source
+(15 rows)
 
 ROLLBACK;
 -- same with a constant qual
@@ -1706,29 +1848,32 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
+   3 |     300 | initial not matched by source
    3 |      30 | inserted by merge
-   3 |     300 | initial
    4 |      40 | inserted by merge
    6 |      60 | inserted by merge
-   7 |     700 | initial
+   7 |     700 | initial not matched by source
    7 |      70 | inserted by merge
    8 |      80 | inserted by merge
-   9 |     900 | initial
+   9 |     900 | initial not matched by source
    9 |      90 | inserted by merge
   10 |     100 | inserted by merge
+  11 |    1100 | initial not matched by source
   11 |     110 | inserted by merge
-  11 |    1100 | initial
   12 |     120 | inserted by merge
-  13 |    1300 | initial
+  13 |    1300 | initial not matched by source
   13 |     130 | inserted by merge
   14 |     140 | inserted by merge
-(18 rows)
+  15 |    1500 | initial not matched by source
+(19 rows)
 
 ROLLBACK;
 -- try updating the partition key column
@@ -1743,30 +1888,33 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 14
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 15
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
+   1 |    1500 | initial not matched by source
    2 |     110 | initial updated by merge
    2 |      20 | inserted by merge
-   4 |      40 | inserted by merge
    4 |     330 | initial updated by merge
+   4 |      40 | inserted by merge
    6 |     550 | initial updated by merge
    6 |      60 | inserted by merge
-   8 |      80 | inserted by merge
    8 |     770 | initial updated by merge
+   8 |      80 | inserted by merge
   10 |     990 | initial updated by merge
   10 |     100 | inserted by merge
   12 |    1210 | initial updated by merge
   12 |     120 | inserted by merge
   14 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+(15 rows)
 
 ROLLBACK;
 -- as above, but blocked by BEFORE DELETE ROW trigger
@@ -1785,15 +1933,17 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 10
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 11
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     100 | initial
    2 |      20 | inserted by merge
    3 |     300 | initial
@@ -1808,7 +1958,8 @@ SELECT * FROM pa_target ORDER BY tid;
   12 |     120 | inserted by merge
   14 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+  15 |    1500 | initial not matched by source
+(15 rows)
 
 ROLLBACK;
 -- as above, but blocked by BEFORE INSERT ROW trigger
@@ -1827,19 +1978,22 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 3
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 4
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    6 |     550 | initial updated by merge
   12 |    1210 | initial updated by merge
   14 |    1430 | initial updated by merge
-(3 rows)
+  15 |    1500 | initial not matched by source
+(4 rows)
 
 ROLLBACK;
 -- test RLS enforcement
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
new file mode 100644
index 0cd2c64..4e45941
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -3718,7 +3718,39 @@ BEGIN ATOMIC
      THEN INSERT (filling[1], id)
       VALUES (s.a, s.a);
 END
+CREATE FUNCTION merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+   USING rule_merge1 s
+   ON (s.a = t.id)
+WHEN NOT MATCHED
+   THEN INSERT (data, id)
+   VALUES (s.a, s.a)
+WHEN MATCHED
+   THEN UPDATE SET data = s.b
+WHEN NOT MATCHED BY SOURCE
+   THEN DELETE;
+END;
+\sf merge_sf_test2
+CREATE OR REPLACE FUNCTION public.merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+    USING rule_merge1 s
+    ON (s.a = t.id)
+    WHEN NOT MATCHED BY TARGET
+     THEN INSERT (data, id)
+      VALUES (s.a, s.a)
+    WHEN MATCHED
+     THEN UPDATE SET data = s.b
+    WHEN NOT MATCHED BY SOURCE
+     THEN DELETE;
+END
 DROP FUNCTION merge_sf_test;
+DROP FUNCTION merge_sf_test2;
 DROP TABLE sf_target;
 --
 -- Test enabling/disabling
diff --git a/src/test/regress/expected/updatable_views.out b/src/test/regress/expected/updatable_views.out
new file mode 100644
index 794cf9c..3a43cce
--- a/src/test/regress/expected/updatable_views.out
+++ b/src/test/regress/expected/updatable_views.out
@@ -491,6 +491,23 @@ SELECT * FROM base_tbl ORDER BY a;
   5 | Unspecified
 (6 rows)
 
+MERGE INTO rw_view1 t
+  USING (VALUES (0, 'R0'), (1, 'R1'),
+                (2, 'R2'), (3, 'R3')) AS v(a,b) ON t.a = v.a
+  WHEN MATCHED AND t.a <= 1 THEN UPDATE SET b = v.b
+  WHEN MATCHED THEN DELETE
+  WHEN NOT MATCHED BY SOURCE THEN DELETE
+  WHEN NOT MATCHED AND a > 0 THEN INSERT (a) VALUES (v.a);
+SELECT * FROM base_tbl ORDER BY a;
+ a  |      b      
+----+-------------
+ -2 | Row -2
+ -1 | Row -1
+  0 | Row 0
+  1 | R1
+  3 | Unspecified
+(5 rows)
+
 EXPLAIN (costs off) UPDATE rw_view1 SET a=6 WHERE a=5;
                     QUERY PLAN                    
 --------------------------------------------------
@@ -537,6 +554,23 @@ MERGE INTO rw_view1 t
 EXPLAIN (costs off)
 MERGE INTO rw_view1 t
   USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
+  WHEN NOT MATCHED BY SOURCE THEN DELETE;
+                            QUERY PLAN                             
+-------------------------------------------------------------------
+ Merge on base_tbl
+   ->  Hash Left Join
+         Hash Cond: (base_tbl.a = generate_series.generate_series)
+         ->  Bitmap Heap Scan on base_tbl
+               Recheck Cond: (a > 0)
+               ->  Bitmap Index Scan on base_tbl_pkey
+                     Index Cond: (a > 0)
+         ->  Hash
+               ->  Function Scan on generate_series
+(9 rows)
+
+EXPLAIN (costs off)
+MERGE INTO rw_view1 t
+  USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
   WHEN NOT MATCHED THEN INSERT (a) VALUES (s.a);
                             QUERY PLAN                             
 -------------------------------------------------------------------
@@ -640,6 +674,20 @@ SELECT * FROM rw_view2 ORDER BY aaa;
    5 | Unspecified
 (3 rows)
 
+MERGE INTO rw_view2 t
+  USING (VALUES (4, 'r4'), (5, 'r5'), (6, 'r6')) AS v(a,b) ON aaa = v.a
+  WHEN MATCHED AND aaa = 4 THEN DELETE
+  WHEN MATCHED THEN UPDATE SET bbb = v.b
+  WHEN NOT MATCHED THEN INSERT (aaa) VALUES (v.a)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET bbb = 'Not matched by source';
+SELECT * FROM rw_view2 ORDER BY aaa;
+ aaa |          bbb          
+-----+-----------------------
+   1 | Not matched by source
+   5 | r5
+   6 | Unspecified
+(3 rows)
+
 EXPLAIN (costs off) UPDATE rw_view2 SET aaa=5 WHERE aaa=4;
                        QUERY PLAN                       
 --------------------------------------------------------
@@ -1082,6 +1130,22 @@ SELECT * FROM base_tbl ORDER BY a;
   3 | R3
 (5 rows)
 
+MERGE INTO rw_view2 t
+  USING (SELECT x, 'r'||x FROM generate_series(0,2) x) AS s(a,b) ON t.a = s.a
+  WHEN MATCHED THEN UPDATE SET b = s.b
+  WHEN NOT MATCHED AND s.a > 0 THEN INSERT VALUES (s.a, s.b)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET b = 'Not matched by source';
+SELECT * FROM base_tbl ORDER BY a;
+ a  |           b           
+----+-----------------------
+ -2 | Row -2
+ -1 | Row -1
+  0 | Row 0
+  1 | r1
+  2 | r2
+  3 | Not matched by source
+(6 rows)
+
 EXPLAIN (costs off) UPDATE rw_view2 SET a=3 WHERE a=2;
                         QUERY PLAN                        
 ----------------------------------------------------------
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index 79a1868..a4607a8
--- a/src/test/regress/sql/merge.sql
+++ b/src/test/regress/sql/merge.sql
@@ -53,6 +53,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN MATCHED THEN
 	INSERT DEFAULT VALUES;
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -77,6 +83,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN NOT MATCHED THEN
 	UPDATE SET balance = 0;
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -214,6 +226,18 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -498,6 +522,17 @@ WHEN NOT MATCHED AND s.balance = 100 THE
 	INSERT (tid) VALUES (s.sid);
 SELECT * FROM wq_target;
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
+
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
 MERGE INTO wq_target t
@@ -625,6 +660,25 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -930,6 +984,20 @@ WHEN MATCHED AND t.a >= 30 AND t.a <= 40
 WHEN NOT MATCHED AND s.a < 20 THEN
 	INSERT VALUES (a, b)');
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
@@ -985,7 +1053,7 @@ CREATE TABLE pa_source (sid integer, del
 -- insert many rows to the source table
 INSERT INTO pa_source SELECT id, id * 10  FROM generate_series(1,14) AS id;
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 
 -- try simple MERGE
 BEGIN;
@@ -995,8 +1063,10 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- same with a constant qual
@@ -1007,8 +1077,10 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- try updating the partition key column
@@ -1023,7 +1095,9 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 IF FOUND THEN
   GET DIAGNOSTICS result := ROW_COUNT;
 END IF;
@@ -1031,7 +1105,7 @@ RETURN result;
 END;
 $$;
 SELECT merge_func();
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 DROP TABLE pa_target CASCADE;
@@ -1057,7 +1131,7 @@ ALTER TABLE pa_target ATTACH PARTITION p
 ALTER TABLE pa_target ATTACH PARTITION part4 DEFAULT;
 
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 
 -- try simple MERGE
 BEGIN;
@@ -1071,12 +1145,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- same with a constant qual
@@ -1088,8 +1164,10 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- try updating the partition key column
@@ -1104,12 +1182,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- as above, but blocked by BEFORE DELETE ROW trigger
@@ -1128,12 +1208,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- as above, but blocked by BEFORE INSERT ROW trigger
@@ -1152,12 +1234,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- test RLS enforcement
diff --git a/src/test/regress/sql/rules.sql b/src/test/regress/sql/rules.sql
new file mode 100644
index 6924012..198b4cd
--- a/src/test/regress/sql/rules.sql
+++ b/src/test/regress/sql/rules.sql
@@ -1336,7 +1336,26 @@ END;
 
 \sf merge_sf_test
 
+CREATE FUNCTION merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+   USING rule_merge1 s
+   ON (s.a = t.id)
+WHEN NOT MATCHED
+   THEN INSERT (data, id)
+   VALUES (s.a, s.a)
+WHEN MATCHED
+   THEN UPDATE SET data = s.b
+WHEN NOT MATCHED BY SOURCE
+   THEN DELETE;
+END;
+
+\sf merge_sf_test2
+
 DROP FUNCTION merge_sf_test;
+DROP FUNCTION merge_sf_test2;
 DROP TABLE sf_target;
 
 --
diff --git a/src/test/regress/sql/updatable_views.sql b/src/test/regress/sql/updatable_views.sql
new file mode 100644
index ae11e46..251eabf
--- a/src/test/regress/sql/updatable_views.sql
+++ b/src/test/regress/sql/updatable_views.sql
@@ -178,6 +178,15 @@ MERGE INTO rw_view1 t
   WHEN NOT MATCHED AND a > 0 THEN INSERT (a) VALUES (v.a);
 SELECT * FROM base_tbl ORDER BY a;
 
+MERGE INTO rw_view1 t
+  USING (VALUES (0, 'R0'), (1, 'R1'),
+                (2, 'R2'), (3, 'R3')) AS v(a,b) ON t.a = v.a
+  WHEN MATCHED AND t.a <= 1 THEN UPDATE SET b = v.b
+  WHEN MATCHED THEN DELETE
+  WHEN NOT MATCHED BY SOURCE THEN DELETE
+  WHEN NOT MATCHED AND a > 0 THEN INSERT (a) VALUES (v.a);
+SELECT * FROM base_tbl ORDER BY a;
+
 EXPLAIN (costs off) UPDATE rw_view1 SET a=6 WHERE a=5;
 EXPLAIN (costs off) DELETE FROM rw_view1 WHERE a=5;
 
@@ -193,6 +202,11 @@ MERGE INTO rw_view1 t
 EXPLAIN (costs off)
 MERGE INTO rw_view1 t
   USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
+  WHEN NOT MATCHED BY SOURCE THEN DELETE;
+
+EXPLAIN (costs off)
+MERGE INTO rw_view1 t
+  USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
   WHEN NOT MATCHED THEN INSERT (a) VALUES (s.a);
 
 -- it's still updatable if we add a DO ALSO rule
@@ -249,6 +263,14 @@ MERGE INTO rw_view2 t
   WHEN NOT MATCHED THEN INSERT (aaa) VALUES (v.a);
 SELECT * FROM rw_view2 ORDER BY aaa;
 
+MERGE INTO rw_view2 t
+  USING (VALUES (4, 'r4'), (5, 'r5'), (6, 'r6')) AS v(a,b) ON aaa = v.a
+  WHEN MATCHED AND aaa = 4 THEN DELETE
+  WHEN MATCHED THEN UPDATE SET bbb = v.b
+  WHEN NOT MATCHED THEN INSERT (aaa) VALUES (v.a)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET bbb = 'Not matched by source';
+SELECT * FROM rw_view2 ORDER BY aaa;
+
 EXPLAIN (costs off) UPDATE rw_view2 SET aaa=5 WHERE aaa=4;
 EXPLAIN (costs off) DELETE FROM rw_view2 WHERE aaa=4;
 
@@ -461,6 +483,13 @@ MERGE INTO rw_view2 t
   WHEN NOT MATCHED AND s.a > 0 THEN INSERT VALUES (s.a, s.b);
 SELECT * FROM base_tbl ORDER BY a;
 
+MERGE INTO rw_view2 t
+  USING (SELECT x, 'r'||x FROM generate_series(0,2) x) AS s(a,b) ON t.a = s.a
+  WHEN MATCHED THEN UPDATE SET b = s.b
+  WHEN NOT MATCHED AND s.a > 0 THEN INSERT VALUES (s.a, s.b)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET b = 'Not matched by source';
+SELECT * FROM base_tbl ORDER BY a;
+
 EXPLAIN (costs off) UPDATE rw_view2 SET a=3 WHERE a=2;
 EXPLAIN (costs off) DELETE FROM rw_view2 WHERE a=2;
 
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
new file mode 100644
index 95ae784..07e2a98
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1573,6 +1573,7 @@ MergeAppendState
 MergeJoin
 MergeJoinClause
 MergeJoinState
+MergeMatchKind
 MergePath
 MergeScanSelCache
 MergeStmt

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
new file mode 100644
index f8f83d4..380d0c9
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -394,10 +394,14 @@
     conditions for each action are re-evaluated on the updated version of
     the row, starting from the first action, even if the action that had
     originally matched appears later in the list of actions.
-    On the other hand, if the row is concurrently updated or deleted so
-    that the join condition fails, then <command>MERGE</command> will
-    evaluate the condition's <literal>NOT MATCHED</literal> actions next,
-    and execute the first one that succeeds.
+    On the other hand, if the row is concurrently updated so that the join
+    condition fails, then <command>MERGE</command> will evaluate the
+    command's <literal>NOT MATCHED BY SOURCE</literal> and
+    <literal>NOT MATCHED [BY TARGET]</literal> actions next, and execute
+    the first one of each kind that succeeds.
+    If the row is concurrently deleted, then <command>MERGE</command>
+    will evaluate the command's <literal>NOT MATCHED [BY TARGET]</literal>
+    actions, and execute the first one that succeeds.
     If <command>MERGE</command> attempts an <command>INSERT</command>
     and a unique index is present and a duplicate row is concurrently
     inserted, then a uniqueness violation error is raised;
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
new file mode 100644
index e745fbd..6845f14
--- a/doc/src/sgml/ref/merge.sgml
+++ b/doc/src/sgml/ref/merge.sgml
@@ -33,7 +33,8 @@ USING <replaceable class="parameter">dat
 <phrase>and <replaceable class="parameter">when_clause</replaceable> is:</phrase>
 
 { WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
-  WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
+  WHEN NOT MATCHED BY SOURCE [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
+  WHEN NOT MATCHED [BY TARGET] [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
 
 <phrase>and <replaceable class="parameter">merge_insert</replaceable> is:</phrase>
 
@@ -72,7 +73,9 @@ DELETE
    from <replaceable class="parameter">data_source</replaceable> to
    the target table
    producing zero or more candidate change rows.  For each candidate change
-   row, the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal>
+   row, the status of <literal>MATCHED</literal>,
+   <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>
    is set just once, after which <literal>WHEN</literal> clauses are evaluated
    in the order specified.  For each candidate change row, the first clause to
    evaluate as true is executed.  No more than one <literal>WHEN</literal>
@@ -254,18 +257,40 @@ DELETE
       At least one <literal>WHEN</literal> clause is required.
      </para>
      <para>
+      The <literal>WHEN</literal> clause may specify <literal>WHEN MATCHED</literal>,
+      <literal>WHEN NOT MATCHED BY SOURCE</literal>, or
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>.
+      Note that the <acronym>SQL</acronym> standard only defines
+      <literal>WHEN MATCHED</literal> and <literal>WHEN NOT MATCHED</literal>
+      (which is defined to mean no matching target row).
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> is an extension to the
+      <acronym>SQL</acronym> standard, as is the option to append
+      <literal>BY TARGET</literal> to <literal>WHEN NOT MATCHED</literal>, to
+      make its meaning more explicit.
+     </para>
+     <para>
       If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
       and the candidate change row matches a row in the
-      target table,
-      the <literal>WHEN</literal> clause is executed if the
+      <replaceable class="parameter">data_source</replaceable> to a row in the
+      target table, the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
      </para>
      <para>
-      Conversely, if the <literal>WHEN</literal> clause specifies
-      <literal>WHEN NOT MATCHED</literal>
-      and the candidate change row does not match a row in the
-      target table,
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> and the candidate change
+      row represents a row in the target table that does not match a row in the
+      <replaceable class="parameter">data_source</replaceable>, the
+      <literal>WHEN</literal> clause is executed if the
+      <replaceable class="parameter">condition</replaceable> is
+      absent or it evaluates to <literal>true</literal>.
+     </para>
+     <para>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal> and the candidate change
+      row represents a row in the
+      <replaceable class="parameter">data_source</replaceable> that does not
+      match a row in the target table,
       the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
@@ -285,7 +310,10 @@ DELETE
      <para>
       A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
       in both the source and the target relations. A condition on a
-      <literal>WHEN NOT MATCHED</literal> clause can only refer to columns from
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> clause can only refer to
+      columns from the target relation, since by definition there is no matching
+      source row. A condition on a <literal>WHEN NOT MATCHED [BY TARGET]</literal>
+      clause can only refer to columns from
       the source relation, since by definition there is no matching target row.
       Only the system attributes from the target table are accessible.
      </para>
@@ -409,8 +437,10 @@ DELETE
       <literal>WHEN MATCHED</literal> clause, the expression can use values
       from the original row in the target table, and values from the
       <replaceable class="parameter">data_source</replaceable> row.
-      If used in a <literal>WHEN NOT MATCHED</literal> clause, the
-      expression can use values from the
+      If used in a <literal>WHEN NOT MATCHED BY SOURCE</literal> clause, the
+      expression can only use values from the original row in the target table.
+      If used in a <literal>WHEN NOT MATCHED [BY TARGET]</literal> clause, the
+      expression can only use values from the
       <replaceable class="parameter">data_source</replaceable> row.
      </para>
     </listitem>
@@ -484,8 +514,9 @@ MERGE <replaceable class="parameter">tot
        <orderedlist>
         <listitem>
          <para>
-          Evaluate whether each row is <literal>MATCHED</literal> or
-          <literal>NOT MATCHED</literal>.
+          Evaluate whether each row is <literal>MATCHED</literal>,
+          <literal>NOT MATCHED BY SOURCE</literal>, or
+          <literal>NOT MATCHED [BY TARGET]</literal>.
          </para>
         </listitem>
         <listitem>
@@ -564,7 +595,8 @@ MERGE <replaceable class="parameter">tot
   <para>
    If a <literal>WHEN</literal> clause omits an <literal>AND</literal>
    sub-clause, it becomes the final reachable clause of that
-   kind (<literal>MATCHED</literal> or <literal>NOT MATCHED</literal>).
+   kind (<literal>MATCHED</literal>, <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>).
    If a later <literal>WHEN</literal> clause of that kind
    is specified it would be provably unreachable and an error is raised.
    If no final reachable clause is specified of either kind, it is
@@ -655,6 +687,23 @@ WHEN MATCHED THEN
    temporary table recently loaded into the database.
   </para>
 
+  <para>
+   Update <literal>wines</literal> based on a replacement wine list, inserting
+   rows for any new stock, updating modified stock entries, and deleting any
+   wines not present in the new list.
+<programlisting>
+MERGE INTO wines w
+USING new_wine_list s
+ON s.winename = w.winename
+WHEN NOT MATCHED BY TARGET THEN
+  INSERT VALUES(s.winename, s.stock)
+WHEN MATCHED AND w.stock != s.stock THEN
+  UPDATE SET stock = s.stock
+WHEN NOT MATCHED BY SOURCE THEN
+  DELETE;
+</programlisting>
+  </para>
+
  </refsect1>
 
  <refsect1>
@@ -663,7 +712,9 @@ WHEN MATCHED THEN
     This command conforms to the <acronym>SQL</acronym> standard.
   </para>
    <para>
-    The <literal>WITH</literal> clause and <literal>DO NOTHING</literal>
+    The <literal>WITH</literal> clause, <literal>BY SOURCE</literal> and
+    <literal>BY TARGET</literal> qualifiers to
+    <literal>WHEN NOT MATCHED</literal>, and <literal>DO NOTHING</literal>
     action are extensions to the <acronym>SQL</acronym> standard.
   </para>
  </refsect1>
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
new file mode 100644
index 940499c..24cb152
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -1245,8 +1245,10 @@ InitResultRelInfo(ResultRelInfo *resultR
 	resultRelInfo->ri_ReturningSlot = NULL;
 	resultRelInfo->ri_TrigOldSlot = NULL;
 	resultRelInfo->ri_TrigNewSlot = NULL;
-	resultRelInfo->ri_matchedMergeAction = NIL;
-	resultRelInfo->ri_notMatchedMergeAction = NIL;
+	resultRelInfo->ri_MergeActions[MERGE_WHEN_MATCHED] = NIL;
+	resultRelInfo->ri_MergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = NIL;
+	resultRelInfo->ri_MergeActions[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = NIL;
+	resultRelInfo->ri_MergeJoinCondition = NULL;
 
 	/*
 	 * Only ExecInitPartitionInfo() and ExecInitPartitionDispatchInfo() pass
diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
new file mode 100644
index 8ca512d..0d83b2f
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -878,6 +878,7 @@ ExecInitPartitionInfo(ModifyTableState *
 		List	   *firstMergeActionList = linitial(node->mergeActionLists);
 		ListCell   *lc;
 		ExprContext *econtext = mtstate->ps.ps_ExprContext;
+		Node	   *joinCondition;
 
 		if (part_attmap == NULL)
 			part_attmap =
@@ -888,23 +889,31 @@ ExecInitPartitionInfo(ModifyTableState *
 		if (unlikely(!leaf_part_rri->ri_projectNewInfoValid))
 			ExecInitMergeTupleSlots(mtstate, leaf_part_rri);
 
+		/* Initialize state for join condition-checking. */
+		joinCondition =
+			map_variable_attnos(linitial(node->mergeJoinConditions),
+								firstVarno, 0,
+								part_attmap,
+								RelationGetForm(partrel)->reltype,
+								&found_whole_row);
+		/* We ignore the value of found_whole_row. */
+		leaf_part_rri->ri_MergeJoinCondition =
+			ExecInitQual((List *) joinCondition, &mtstate->ps);
+
 		foreach(lc, firstMergeActionList)
 		{
 			/* Make a copy for this relation to be safe.  */
 			MergeAction *action = copyObject(lfirst(lc));
 			MergeActionState *action_state;
-			List	  **list;
 
 			/* Generate the action's state for this relation */
 			action_state = makeNode(MergeActionState);
 			action_state->mas_action = action;
 
 			/* And put the action in the appropriate list */
-			if (action->matched)
-				list = &leaf_part_rri->ri_matchedMergeAction;
-			else
-				list = &leaf_part_rri->ri_notMatchedMergeAction;
-			*list = lappend(*list, action_state);
+			leaf_part_rri->ri_MergeActions[action->matchKind] =
+				lappend(leaf_part_rri->ri_MergeActions[action->matchKind],
+						action_state);
 
 			switch (action->commandType)
 			{
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
new file mode 100644
index 9351fbc..7e19bae
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -24,13 +24,15 @@
  *		values plus row-locating info for UPDATE and MERGE cases, or just the
  *		row-locating info for DELETE cases.
  *
- *		MERGE runs a join between the source relation and the target
- *		table; if any WHEN NOT MATCHED clauses are present, then the
- *		join is an outer join.  In this case, any unmatched tuples will
- *		have NULL row-locating info, and only INSERT can be run. But for
- *		matched tuples, then row-locating info is used to determine the
- *		tuple to UPDATE or DELETE. When all clauses are WHEN MATCHED,
- *		then an inner join is used, so all tuples contain row-locating info.
+ *		MERGE runs a join between the source relation and the target table.
+ *		If any WHEN NOT MATCHED [BY TARGET] clauses are present, then the join
+ *		is an outer join that might output tuples without a matching target
+ *		tuple.  In this case, any unmatched target tuples will have NULL
+ *		row-locating info, and only INSERT can be run.  But for matched
+ *		target tuples, the row-locating info is used to determine the tuple
+ *		to UPDATE or DELETE.  When all clauses are WHEN MATCHED or WHEN NOT
+ *		MATCHED BY SOURCE, all tuples produced by the join will include a
+ *		matching target tuple, so all tuples contain row-locating info.
  *
  *		If the query specifies RETURNING, then the ModifyTable returns a
  *		RETURNING tuple after completing each row insert, update, or delete.
@@ -2716,48 +2718,61 @@ ExecMerge(ModifyTableContext *context, R
 	bool		matched;
 
 	/*-----
-	 * If we are dealing with a WHEN MATCHED case (tupleid or oldtuple is
-	 * valid, depending on whether the result relation is a table or a view),
-	 * we execute the first action for which the additional WHEN MATCHED AND
+	 * If we are dealing with a WHEN MATCHED case, tupleid or oldtuple is
+	 * valid, depending on whether the result relation is a table or a view.
+	 * We execute the first action for which the additional WHEN MATCHED AND
 	 * quals pass.  If an action without quals is found, that action is
 	 * executed.
 	 *
-	 * Similarly, if we are dealing with WHEN NOT MATCHED case, we look at
-	 * the given WHEN NOT MATCHED actions in sequence until one passes.
+	 * Similarly, in the WHEN NOT MATCHED BY SOURCE case, tupleid or oldtuple
+	 * is valid, and we look at the given WHEN NOT MATCHED BY SOURCE actions
+	 * in sequence until one passes.  This is almost identical to the WHEN
+	 * MATCHED case, and both cases are handled by ExecMergeMatched().
+	 *
+	 * Finally, in the WHEN NOT MATCHED [BY TARGET] case, both tupleid and
+	 * oldtuple are invalid, and we look at the given WHEN NOT MATCHED [BY
+	 * TARGET] actions in sequence until one passes.
 	 *
 	 * Things get interesting in case of concurrent update/delete of the
 	 * target tuple. Such concurrent update/delete is detected while we are
-	 * executing a WHEN MATCHED action.
+	 * executing a WHEN MATCHED or WHEN NOT MATCHED BY SOURCE action.
 	 *
 	 * A concurrent update can:
 	 *
 	 * 1. modify the target tuple so that it no longer satisfies the
-	 *    additional quals attached to the current WHEN MATCHED action
+	 *    additional quals attached to the current WHEN MATCHED or WHEN NOT
+	 *    MATCHED BY SOURCE action, but still satisfies the join quals.
 	 *
-	 *    In this case, we are still dealing with a WHEN MATCHED case.
-	 *    We recheck the list of WHEN MATCHED actions from the start and
-	 *    choose the first one that satisfies the new target tuple.
+	 *    In this case, we are still dealing with the same kind of match
+	 *    (MATCHED or NOT MATCHED BY SOURCE).  We recheck the same list of
+	 *    actions from the start and choose the first one that satisfies the
+	 *    new target tuple.
 	 *
 	 * 2. modify the target tuple so that the join quals no longer pass and
-	 *    hence the source tuple no longer has a match.
+	 *    hence the source and target tuples no longer match.
 	 *
-	 *    In this case, the source tuple no longer matches the target tuple,
-	 *    so we now instead find a qualifying WHEN NOT MATCHED action to
-	 *    execute.
+	 *    In this case, we are now dealing with a NOT MATCHED case, and we
+	 *    process both WHEN NOT MATCHED BY SOURCE and WHEN NOT MATCHED [BY
+	 *    TARGET] actions.  First ExecMergeMatched() processes the list of
+	 *    WHEN NOT MATCHED BY SOURCE actions in sequence until one passes,
+	 *    then ExecMergeNotMatched() processes any WHEN NOT MATCHED [BY
+	 *    TARGET] actions in sequence until one passes.  Thus we may execute
+	 *    two actions; one of each kind.
 	 *
 	 * XXX Hmmm, what if the updated tuple would now match one that was
 	 * considered NOT MATCHED so far?
 	 *
-	 * A concurrent delete changes a WHEN MATCHED case to WHEN NOT MATCHED.
+	 * A concurrent delete changes a WHEN MATCHED case to WHEN NOT MATCHED
+	 * [BY TARGET].
 	 *
 	 * ExecMergeMatched takes care of following the update chain and
-	 * re-finding the qualifying WHEN MATCHED action, as long as the updated
-	 * target tuple still satisfies the join quals, i.e., it remains a WHEN
-	 * MATCHED case. If the tuple gets deleted or the join quals fail, it
-	 * returns and we try ExecMergeNotMatched. Given that ExecMergeMatched
-	 * always make progress by following the update chain and we never switch
-	 * from ExecMergeNotMatched to ExecMergeMatched, there is no risk of a
-	 * livelock.
+	 * re-finding the qualifying WHEN MATCHED or WHEN NOT MATCHED BY SOURCE
+	 * action, as long as the target tuple still exists. If the target tuple
+	 * gets deleted or a concurrent update causes the join quals to fail, it
+	 * returns a matched status of false and we call ExecMergeNotMatched.
+	 * Given that ExecMergeMatched always makes progress by following the
+	 * update chain and we never switch from ExecMergeNotMatched to
+	 * ExecMergeMatched, there is no risk of a livelock.
 	 */
 	matched = tupleid != NULL || oldtuple != NULL;
 	if (matched)
@@ -2777,85 +2792,103 @@ ExecMerge(ModifyTableContext *context, R
 }
 
 /*
- * Check and execute the first qualifying MATCHED action.  If the target
+ * Check and execute the first qualifying MATCHED or NOT MATCHED BY SOURCE
+ * action, depending on whether the join quals are satisfied.  If the target
  * relation is a table, the current target tuple is identified by tupleid.
  * Otherwise, if the target relation is a view, oldtuple is the current target
  * tuple from the view.
  *
- * We start from the first WHEN MATCHED action and check if the WHEN quals
- * pass, if any. If the WHEN quals for the first action do not pass, we
- * check the second, then the third and so on. If we reach to the end, no
- * action is taken and we return true, indicating that no further action is
- * required for this tuple.
+ * We start from the first WHEN MATCHED or WHEN NOT MATCHED BY SOURCE action
+ * and check if the WHEN quals pass, if any. If the WHEN quals for the first
+ * action do not pass, we check the second, then the third and so on. If we
+ * reach to the end, no action is taken and we return true, indicating that no
+ * further action is required for this tuple.
  *
  * If we do find a qualifying action, then we attempt to execute the action.
  *
- * If the tuple is concurrently updated, EvalPlanQual is run with the updated
- * tuple to recheck the join quals. Note that the additional quals associated
- * with individual actions are evaluated by this routine via ExecQual, while
- * EvalPlanQual checks for the join quals. If EvalPlanQual tells us that the
- * updated tuple still passes the join quals, then we restart from the first
- * action to look for a qualifying action. Otherwise, we return false --
- * meaning that a NOT MATCHED action must now be executed for the current
- * source tuple.
+ * If the tuple is concurrently updated, and we were dealing with the MATCHED
+ * case, EvalPlanQual is run with the updated tuple to recheck the join quals.
+ * If the join quals no longer pass, we switch from the MATCHED case to the
+ * WHEN NOT MATCHED BY SOURCE case. Then we restart from the first action to
+ * look for a qualifying action. If we switched from matched to not matched,
+ * then we return false, indicating that a NOT MATCHED [BY TARGET] action must
+ * now be executed for the current source tuple (possibly in addition to any
+ * NOT MATCHED BY SOURCE action executed here).
  */
 static bool
 ExecMergeMatched(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
 				 ItemPointer tupleid, HeapTuple oldtuple, bool canSetTag)
 {
 	ModifyTableState *mtstate = context->mtstate;
+	List	  **mergeActions = resultRelInfo->ri_MergeActions;
+	List	   *actionStates;
 	TupleTableSlot *newslot;
 	EState	   *estate = context->estate;
 	ExprContext *econtext = mtstate->ps.ps_ExprContext;
 	bool		isNull;
 	EPQState   *epqstate = &mtstate->mt_epqstate;
+	bool		epq_ok;
 	ListCell   *l;
 
 	/*
-	 * If there are no WHEN MATCHED actions, we are done.
+	 * If there are no WHEN MATCHED or WHEN NOT MATCHED BY SOURCE actions, we
+	 * are done.
 	 */
-	if (resultRelInfo->ri_matchedMergeAction == NIL)
+	if (mergeActions[MERGE_WHEN_MATCHED] == NIL &&
+		mergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] == NIL)
 		return true;
 
 	/*
 	 * Make tuple and any needed join variables available to ExecQual and
 	 * ExecProject. The target's existing tuple is installed in the scantuple.
-	 * Again, this target relation's slot is required only in the case of a
-	 * MATCHED tuple and UPDATE/DELETE actions.
+	 * This target relation's slot is required only in the case of a MATCHED
+	 * or NOT MATCHED BY SOURCE tuple and UPDATE/DELETE actions.
 	 */
 	econtext->ecxt_scantuple = resultRelInfo->ri_oldTupleSlot;
 	econtext->ecxt_innertuple = context->planSlot;
 	econtext->ecxt_outertuple = NULL;
 
 	/*
-	 * This routine is only invoked for matched rows, so we should either have
-	 * the tupleid of the target row, or an old tuple from the target wholerow
-	 * junk attr.
+	 * This routine is only invoked for matched target rows, so we should
+	 * either have the tupleid of the target row, or an old tuple from the
+	 * target wholerow junk attr.
 	 */
 	Assert(tupleid != NULL || oldtuple != NULL);
 	if (oldtuple != NULL)
 		ExecForceStoreHeapTuple(oldtuple, resultRelInfo->ri_oldTupleSlot,
 								false);
-
-lmerge_matched:
+	else if (!table_tuple_fetch_row_version(resultRelInfo->ri_RelationDesc,
+											tupleid,
+											SnapshotAny,
+											resultRelInfo->ri_oldTupleSlot))
+		elog(ERROR, "failed to fetch the target tuple");
 
 	/*
-	 * If passed a tupleid, use it to fetch the old target row.
+	 * Test the join condition.  If it's satisfied, perform a MATCHED action;
+	 * otherwise, perform a NOT MATCHED BY SOURCE action.
 	 *
-	 * We use SnapshotAny for this because we might get called again after
-	 * EvalPlanQual returns us a new tuple, which may not be visible to our
-	 * MVCC snapshot.
+	 * Note that this join condition will be NULL if there are no NOT MATCHED
+	 * BY SOURCE actions --- see transform_MERGE_to_join().  In that case, the
+	 * join subplan will only output MATCHED and NOT MATCHED [BY TARGET] rows,
+	 * and we only need to process MATCHED actions here.
 	 */
-	if (tupleid != NULL)
-	{
-		if (!table_tuple_fetch_row_version(resultRelInfo->ri_RelationDesc,
-										   tupleid,
-										   SnapshotAny,
-										   resultRelInfo->ri_oldTupleSlot))
-			elog(ERROR, "failed to fetch the target tuple");
-	}
+	if (ExecQual(resultRelInfo->ri_MergeJoinCondition, econtext))
+		actionStates = mergeActions[MERGE_WHEN_MATCHED];
+	else
+		actionStates = mergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE];
 
-	foreach(l, resultRelInfo->ri_matchedMergeAction)
+	/*
+	 * A concurrent update may change the target tuple so that a MATCHED row
+	 * becomes NOT MATCHED BY SOURCE (but not vice versa).  If this happens,
+	 * we set epq_ok = false, process the NOT MATCHED BY SOURCE actions, and
+	 * then return false to indicate that the caller must also process any NOT
+	 * MATCHED [BY TARGET] actions.
+	 */
+	epq_ok = true;
+
+lmerge_matched:
+
+	foreach(l, actionStates)
 	{
 		MergeActionState *relaction = (MergeActionState *) lfirst(l);
 		CmdType		commandType = relaction->mas_action->commandType;
@@ -2910,7 +2943,7 @@ lmerge_matched:
 										tupleid, NULL, newslot, &result))
 				{
 					if (result == TM_Ok)
-						return true;	/* "do nothing" */
+						return epq_ok;	/* "do nothing" */
 					break;		/* concurrent update/delete */
 				}
 
@@ -2920,7 +2953,7 @@ lmerge_matched:
 				{
 					if (!ExecIRUpdateTriggers(estate, resultRelInfo,
 											  oldtuple, newslot))
-						return true;	/* "do nothing" */
+						return epq_ok;	/* "do nothing" */
 				}
 				else
 				{
@@ -2938,7 +2971,7 @@ lmerge_matched:
 					if (updateCxt.crossPartUpdate)
 					{
 						mtstate->mt_merge_updated += 1;
-						return true;
+						return epq_ok;
 					}
 				}
 
@@ -2956,7 +2989,7 @@ lmerge_matched:
 										NULL, NULL, &result))
 				{
 					if (result == TM_Ok)
-						return true;	/* "do nothing" */
+						return epq_ok;	/* "do nothing" */
 					break;		/* concurrent update/delete */
 				}
 
@@ -2966,7 +2999,7 @@ lmerge_matched:
 				{
 					if (!ExecIRDeleteTriggers(estate, resultRelInfo,
 											  oldtuple))
-						return true;	/* "do nothing" */
+						return epq_ok;	/* "do nothing" */
 				}
 				else
 					result = ExecDeleteAct(context, resultRelInfo, tupleid,
@@ -2986,7 +3019,7 @@ lmerge_matched:
 				break;
 
 			default:
-				elog(ERROR, "unknown action in MERGE WHEN MATCHED clause");
+				elog(ERROR, "unknown action in MERGE WHEN clause");
 		}
 
 		switch (result)
@@ -3044,12 +3077,13 @@ lmerge_matched:
 
 				/*
 				 * If the tuple was already deleted, return to let caller
-				 * handle it under NOT MATCHED clauses.
+				 * handle it under NOT MATCHED [BY TARGET] clauses.
 				 */
 				return false;
 
 			case TM_Updated:
 				{
+					bool		was_matched;
 					Relation	resultRelationDesc;
 					TupleTableSlot *epqslot,
 							   *inputslot;
@@ -3057,19 +3091,22 @@ lmerge_matched:
 
 					/*
 					 * The target tuple was concurrently updated by some other
-					 * transaction. Run EvalPlanQual() with the new version of
-					 * the tuple. If it does not return a tuple, then we
-					 * switch to the NOT MATCHED list of actions. If it does
-					 * return a tuple and the join qual is still satisfied,
-					 * then we just need to recheck the MATCHED actions,
-					 * starting from the top, and execute the first qualifying
-					 * action.
+					 * transaction.  If we are currently processing a MATCHED
+					 * action, use EvalPlanQual() with the new version of the
+					 * tuple and recheck the join qual, to detect a change
+					 * from the MATCHED to the NOT MATCHED cases.  If we are
+					 * already processing a NOT MATCHED BY SOURCE action, this
+					 * is not necessary.
 					 */
+					was_matched = relaction->mas_action->matchKind == MERGE_WHEN_MATCHED;
 					resultRelationDesc = resultRelInfo->ri_RelationDesc;
 					lockmode = ExecUpdateLockMode(estate, resultRelInfo);
 
-					inputslot = EvalPlanQualSlot(epqstate, resultRelationDesc,
-												 resultRelInfo->ri_RangeTableIndex);
+					if (was_matched)
+						inputslot = EvalPlanQualSlot(epqstate, resultRelationDesc,
+													 resultRelInfo->ri_RangeTableIndex);
+					else
+						inputslot = resultRelInfo->ri_oldTupleSlot;
 
 					result = table_tuple_lock(resultRelationDesc, tupleid,
 											  estate->es_snapshot,
@@ -3080,28 +3117,9 @@ lmerge_matched:
 					switch (result)
 					{
 						case TM_Ok:
-							epqslot = EvalPlanQual(epqstate,
-												   resultRelationDesc,
-												   resultRelInfo->ri_RangeTableIndex,
-												   inputslot);
-
-							/*
-							 * If we got no tuple, or the tuple we get has a
-							 * NULL ctid, go back to caller: this one is not a
-							 * MATCHED tuple anymore, so they can retry with
-							 * NOT MATCHED actions.
-							 */
-							if (TupIsNull(epqslot))
-								return false;
-
-							(void) ExecGetJunkAttribute(epqslot,
-														resultRelInfo->ri_RowIdAttNo,
-														&isNull);
-							if (isNull)
-								return false;
 
 							/*
-							 * When a tuple was updated and migrated to
+							 * If the tuple was updated and migrated to
 							 * another partition concurrently, the current
 							 * MERGE implementation can't follow.  There's
 							 * probably a better way to handle this case, but
@@ -3112,26 +3130,72 @@ lmerge_matched:
 							if (ItemPointerIndicatesMovedPartitions(&context->tmfd.ctid))
 								ereport(ERROR,
 										(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
-										 errmsg("tuple to be deleted was already moved to another partition due to concurrent update")));
+										 errmsg("tuple to be merged was already moved to another partition due to concurrent update")));
 
 							/*
-							 * A non-NULL ctid means that we are still dealing
-							 * with MATCHED case. Restart the loop so that we
-							 * apply all the MATCHED rules again, to ensure
-							 * that the first qualifying WHEN MATCHED action
-							 * is executed.
-							 *
-							 * Update tupleid to that of the new tuple, for
-							 * the refetch we do at the top.
+							 * If this was a MATCHED case, use EvalPlanQual()
+							 * to recheck the join condition.
+							 */
+							if (was_matched)
+							{
+								epqslot = EvalPlanQual(epqstate,
+													   resultRelationDesc,
+													   resultRelInfo->ri_RangeTableIndex,
+													   inputslot);
+
+								/*
+								 * If the subplan didn't return a tuple, then
+								 * we must be dealing with an inner join for
+								 * which the join condition no longer matches.
+								 * This can only happen if there are no NOT
+								 * MATCHED actions, and so there is nothing
+								 * more for us to do.
+								 */
+								if (TupIsNull(epqslot))
+									return true;
+
+								/*
+								 * If we got a NULL ctid from the subplan, the
+								 * join quals no longer pass and we switch to
+								 * the NOT MATCHED BY SOURCE case.
+								 */
+								(void) ExecGetJunkAttribute(epqslot,
+															resultRelInfo->ri_RowIdAttNo,
+															&isNull);
+								if (isNull)
+									epq_ok = false;
+
+								/*
+								 * Otherwise, recheck the join quals to see if
+								 * we need to switch to the NOT MATCHED BY
+								 * SOURCE case.
+								 */
+								if (!table_tuple_fetch_row_version(resultRelationDesc,
+																   &context->tmfd.ctid,
+																   SnapshotAny,
+																   resultRelInfo->ri_oldTupleSlot))
+									elog(ERROR, "failed to fetch the target tuple");
+
+								if (epq_ok)
+									epq_ok = ExecQual(resultRelInfo->ri_MergeJoinCondition,
+													  econtext);
+
+								/* Switch lists, if necessary */
+								if (!epq_ok)
+									actionStates = mergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE];
+							}
+
+							/*
+							 * Loop back and process the MATCHED or NOT
+							 * MATCHED BY SOURCE actions from the start.
 							 */
-							ItemPointerCopy(&context->tmfd.ctid, tupleid);
 							goto lmerge_matched;
 
 						case TM_Deleted:
 
 							/*
 							 * tuple already deleted; tell caller to run NOT
-							 * MATCHED actions
+							 * MATCHED [BY TARGET] actions
 							 */
 							return false;
 
@@ -3189,11 +3253,11 @@ lmerge_matched:
 	/*
 	 * Successfully executed an action or no qualifying action was found.
 	 */
-	return true;
+	return epq_ok;
 }
 
 /*
- * Execute the first qualifying NOT MATCHED action.
+ * Execute the first qualifying NOT MATCHED [BY TARGET] action.
  */
 static void
 ExecMergeNotMatched(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
@@ -3201,7 +3265,7 @@ ExecMergeNotMatched(ModifyTableContext *
 {
 	ModifyTableState *mtstate = context->mtstate;
 	ExprContext *econtext = mtstate->ps.ps_ExprContext;
-	List	   *actionStates = NIL;
+	List	   *actionStates;
 	ListCell   *l;
 
 	/*
@@ -3213,7 +3277,7 @@ ExecMergeNotMatched(ModifyTableContext *
 	 * XXX does this mean that we can avoid creating copies of actionStates on
 	 * partitioned tables, for not-matched actions?
 	 */
-	actionStates = resultRelInfo->ri_notMatchedMergeAction;
+	actionStates = resultRelInfo->ri_MergeActions[MERGE_WHEN_NOT_MATCHED_BY_TARGET];
 
 	/*
 	 * Make source tuple available to ExecQual and ExecProject. We don't need
@@ -3305,9 +3369,11 @@ ExecInitMerge(ModifyTableState *mtstate,
 	foreach(lc, node->mergeActionLists)
 	{
 		List	   *mergeActionList = lfirst(lc);
+		Node	   *joinCondition;
 		TupleDesc	relationDesc;
 		ListCell   *l;
 
+		joinCondition = (Node *) list_nth(node->mergeJoinConditions, i);
 		resultRelInfo = mtstate->resultRelInfo + i;
 		i++;
 		relationDesc = RelationGetDescr(resultRelInfo->ri_RelationDesc);
@@ -3316,13 +3382,16 @@ ExecInitMerge(ModifyTableState *mtstate,
 		if (unlikely(!resultRelInfo->ri_projectNewInfoValid))
 			ExecInitMergeTupleSlots(mtstate, resultRelInfo);
 
+		/* initialize state for join condition-checking */
+		resultRelInfo->ri_MergeJoinCondition =
+			ExecInitQual((List *) joinCondition, &mtstate->ps);
+
 		foreach(l, mergeActionList)
 		{
 			MergeAction *action = (MergeAction *) lfirst(l);
 			MergeActionState *action_state;
 			TupleTableSlot *tgtslot;
 			TupleDesc	tgtdesc;
-			List	  **list;
 
 			/*
 			 * Build action merge state for this rel.  (For partitions,
@@ -3334,15 +3403,12 @@ ExecInitMerge(ModifyTableState *mtstate,
 													  &mtstate->ps);
 
 			/*
-			 * We create two lists - one for WHEN MATCHED actions and one for
-			 * WHEN NOT MATCHED actions - and stick the MergeActionState into
-			 * the appropriate list.
+			 * We create three lists - one for each MergeMatchKind - and stick
+			 * the MergeActionState into the appropriate list.
 			 */
-			if (action_state->mas_action->matched)
-				list = &resultRelInfo->ri_matchedMergeAction;
-			else
-				list = &resultRelInfo->ri_notMatchedMergeAction;
-			*list = lappend(*list, action_state);
+			resultRelInfo->ri_MergeActions[action->matchKind] =
+				lappend(resultRelInfo->ri_MergeActions[action->matchKind],
+						action_state);
 
 			switch (action->commandType)
 			{
diff --git a/src/backend/nodes/nodeFuncs.c b/src/backend/nodes/nodeFuncs.c
new file mode 100644
index 6ba8e73..1900156
--- a/src/backend/nodes/nodeFuncs.c
+++ b/src/backend/nodes/nodeFuncs.c
@@ -2583,6 +2583,8 @@ query_tree_walker_impl(Query *query,
 		return true;
 	if (WALK(query->mergeActionList))
 		return true;
+	if (WALK(query->mergeJoinCondition))
+		return true;
 	if (WALK(query->returningList))
 		return true;
 	if (WALK(query->jointree))
@@ -3607,6 +3609,7 @@ query_tree_mutator_impl(Query *query,
 	MUTATE(query->withCheckOptions, query->withCheckOptions, List *);
 	MUTATE(query->onConflict, query->onConflict, OnConflictExpr *);
 	MUTATE(query->mergeActionList, query->mergeActionList, List *);
+	MUTATE(query->mergeJoinCondition, query->mergeJoinCondition, Node *);
 	MUTATE(query->returningList, query->returningList, List *);
 	MUTATE(query->jointree, query->jointree, FromExpr *);
 	MUTATE(query->setOperations, query->setOperations, Node *);
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
new file mode 100644
index 610f4a5..1d36665
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -311,7 +311,8 @@ static ModifyTable *make_modifytable(Pla
 									 List *updateColnosLists,
 									 List *withCheckOptionLists, List *returningLists,
 									 List *rowMarks, OnConflictExpr *onconflict,
-									 List *mergeActionLists, int epqParam);
+									 List *mergeActionLists, List *mergeJoinConditions,
+									 int epqParam);
 static GatherMerge *create_gather_merge_plan(PlannerInfo *root,
 											 GatherMergePath *best_path);
 
@@ -2835,6 +2836,7 @@ create_modifytable_plan(PlannerInfo *roo
 							best_path->rowMarks,
 							best_path->onconflict,
 							best_path->mergeActionLists,
+							best_path->mergeJoinConditions,
 							best_path->epqParam);
 
 	copy_generic_path_info(&plan->plan, &best_path->path);
@@ -7014,7 +7016,8 @@ make_modifytable(PlannerInfo *root, Plan
 				 List *updateColnosLists,
 				 List *withCheckOptionLists, List *returningLists,
 				 List *rowMarks, OnConflictExpr *onconflict,
-				 List *mergeActionLists, int epqParam)
+				 List *mergeActionLists, List *mergeJoinConditions,
+				 int epqParam)
 {
 	ModifyTable *node = makeNode(ModifyTable);
 	List	   *fdw_private_list;
@@ -7084,6 +7087,7 @@ make_modifytable(PlannerInfo *root, Plan
 	node->returningLists = returningLists;
 	node->rowMarks = rowMarks;
 	node->mergeActionLists = mergeActionLists;
+	node->mergeJoinConditions = mergeJoinConditions;
 	node->epqParam = epqParam;
 
 	/*
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
new file mode 100644
index 443ab08..99c0603
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -905,6 +905,9 @@ subquery_planner(PlannerGlobal *glob, Qu
 								  EXPRKIND_QUAL);
 	}
 
+	parse->mergeJoinCondition =
+		preprocess_expression(root, parse->mergeJoinCondition, EXPRKIND_QUAL);
+
 	root->append_rel_list = (List *)
 		preprocess_expression(root, (Node *) root->append_rel_list,
 							  EXPRKIND_APPINFO);
@@ -1787,6 +1790,7 @@ grouping_planner(PlannerInfo *root, doub
 			List	   *withCheckOptionLists = NIL;
 			List	   *returningLists = NIL;
 			List	   *mergeActionLists = NIL;
+			List	   *mergeJoinConditions = NIL;
 			List	   *rowMarks;
 
 			if (bms_membership(root->all_result_relids) == BMS_MULTIPLE)
@@ -1893,6 +1897,19 @@ grouping_planner(PlannerInfo *root, doub
 						mergeActionLists = lappend(mergeActionLists,
 												   mergeActionList);
 					}
+					if (parse->commandType == CMD_MERGE)
+					{
+						Node	   *mergeJoinCondition = parse->mergeJoinCondition;
+
+						if (this_result_rel != top_result_rel)
+							mergeJoinCondition =
+								adjust_appendrel_attrs_multilevel(root,
+																  mergeJoinCondition,
+																  this_result_rel,
+																  top_result_rel);
+						mergeJoinConditions = lappend(mergeJoinConditions,
+													  mergeJoinCondition);
+					}
 				}
 
 				if (resultRelations == NIL)
@@ -1917,6 +1934,8 @@ grouping_planner(PlannerInfo *root, doub
 						returningLists = list_make1(parse->returningList);
 					if (parse->mergeActionList)
 						mergeActionLists = list_make1(parse->mergeActionList);
+					if (parse->commandType == CMD_MERGE)
+						mergeJoinConditions = list_make1(parse->mergeJoinCondition);
 				}
 			}
 			else
@@ -1932,6 +1951,8 @@ grouping_planner(PlannerInfo *root, doub
 					returningLists = list_make1(parse->returningList);
 				if (parse->mergeActionList)
 					mergeActionLists = list_make1(parse->mergeActionList);
+				if (parse->commandType == CMD_MERGE)
+					mergeJoinConditions = list_make1(parse->mergeJoinCondition);
 			}
 
 			/*
@@ -1959,6 +1980,7 @@ grouping_planner(PlannerInfo *root, doub
 										rowMarks,
 										parse->onConflict,
 										mergeActionLists,
+										mergeJoinConditions,
 										assign_special_exec_param(root));
 		}
 
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
new file mode 100644
index 42603db..37abcb4
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -1143,7 +1143,9 @@ set_plan_refs(PlannerInfo *root, Plan *p
 				 */
 				if (splan->mergeActionLists != NIL)
 				{
+					List	   *newMJC = NIL;
 					ListCell   *lca,
+							   *lcj,
 							   *lcr;
 
 					/*
@@ -1164,10 +1166,12 @@ set_plan_refs(PlannerInfo *root, Plan *p
 
 					itlist = build_tlist_index(subplan->targetlist);
 
-					forboth(lca, splan->mergeActionLists,
-							lcr, splan->resultRelations)
+					forthree(lca, splan->mergeActionLists,
+							 lcj, splan->mergeJoinConditions,
+							 lcr, splan->resultRelations)
 					{
 						List	   *mergeActionList = lfirst(lca);
+						Node	   *mergeJoinCondition = lfirst(lcj);
 						Index		resultrel = lfirst_int(lcr);
 
 						foreach(l, mergeActionList)
@@ -1192,7 +1196,19 @@ set_plan_refs(PlannerInfo *root, Plan *p
 																  NRM_EQUAL,
 																  NUM_EXEC_QUAL(plan));
 						}
+
+						/* Fix join condition too. */
+						mergeJoinCondition = (Node *)
+							fix_join_expr(root,
+										  (List *) mergeJoinCondition,
+										  NULL, itlist,
+										  resultrel,
+										  rtoffset,
+										  NRM_EQUAL,
+										  NUM_EXEC_QUAL(plan));
+						newMJC = lappend(newMJC, mergeJoinCondition);
 					}
+					splan->mergeJoinConditions = newMJC;
 				}
 
 				splan->nominalRelation += rtoffset;
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
new file mode 100644
index 300691c..2d8956d
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -153,9 +153,11 @@ transform_MERGE_to_join(Query *parse)
 {
 	RangeTblEntry *joinrte;
 	JoinExpr   *joinexpr;
+	bool		have_action[3];
 	JoinType	jointype;
 	int			joinrti;
 	List	   *vars;
+	RangeTblRef *rtr;
 
 	if (parse->commandType != CMD_MERGE)
 		return;
@@ -164,11 +166,27 @@ transform_MERGE_to_join(Query *parse)
 	vars = NIL;
 
 	/*
-	 * When any WHEN NOT MATCHED THEN INSERT clauses exist, we need to use an
-	 * outer join so that we process all unmatched tuples from the source
-	 * relation.  If none exist, we can use an inner join.
+	 * Work out what kind of join is required.  If there any WHEN NOT MATCHED
+	 * BY SOURCE/TARGET actions, an outer join is required so that we process
+	 * all unmatched tuples from the source and/or target relations.
+	 * Otherwise, we can use an inner join.
 	 */
-	if (parse->mergeUseOuterJoin)
+	have_action[MERGE_WHEN_MATCHED] = false;
+	have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	have_action[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
+
+	foreach_node(MergeAction, action, parse->mergeActionList)
+	{
+		if (action->commandType != CMD_NOTHING)
+			have_action[action->matchKind] = true;
+	}
+
+	if (have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] &&
+		have_action[MERGE_WHEN_NOT_MATCHED_BY_TARGET])
+		jointype = JOIN_FULL;
+	else if (have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE])
+		jointype = JOIN_LEFT;
+	else if (have_action[MERGE_WHEN_NOT_MATCHED_BY_TARGET])
 		jointype = JOIN_RIGHT;
 	else
 		jointype = JOIN_INNER;
@@ -204,16 +222,16 @@ transform_MERGE_to_join(Query *parse)
 	 * trigger-updatable view, it will be the expanded view subquery that we
 	 * need to pull data from.
 	 */
+	rtr = makeNode(RangeTblRef);
+	rtr->rtindex = parse->mergeTargetRelation;
 	joinexpr = makeNode(JoinExpr);
 	joinexpr->jointype = jointype;
 	joinexpr->isNatural = false;
-	joinexpr->larg = (Node *) makeNode(RangeTblRef);
-	((RangeTblRef *) joinexpr->larg)->rtindex = parse->mergeTargetRelation;
-	joinexpr->rarg = linitial(parse->jointree->fromlist);	/* original join */
+	joinexpr->larg = (Node *) makeFromExpr(list_make1(rtr), parse->jointree->quals);
+	joinexpr->rarg = linitial(parse->jointree->fromlist);	/* source rel */
 	joinexpr->usingClause = NIL;
 	joinexpr->join_using_alias = NULL;
-	/* The quals are removed from the jointree and into this specific join */
-	joinexpr->quals = parse->jointree->quals;
+	joinexpr->quals = parse->mergeJoinCondition;
 	joinexpr->alias = NULL;
 	joinexpr->rtindex = joinrti;
 
@@ -233,6 +251,15 @@ transform_MERGE_to_join(Query *parse)
 			add_nulling_relids((Node *) parse->targetList,
 							   bms_make_singleton(parse->mergeTargetRelation),
 							   bms_make_singleton(joinrti));
+
+	/*
+	 * If there are any WHEN NOT MATCHED BY SOURCE actions, the executor will
+	 * use the join condition to distinguish between MATCHED and NOT MATCHED
+	 * BY SOURCE cases.  Otherwise, it's no longer needed, and we set it to
+	 * NULL, saving cycles during planning and execution.
+	 */
+	if (!have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE])
+		parse->mergeJoinCondition = NULL;
 }
 
 /*
@@ -2173,6 +2200,8 @@ perform_pullup_replace_vars(PlannerInfo
 				pullup_replace_vars((Node *) action->targetList, rvcontext);
 		}
 	}
+	parse->mergeJoinCondition = pullup_replace_vars(parse->mergeJoinCondition,
+													rvcontext);
 	replace_vars_in_jointree((Node *) parse->jointree, rvcontext);
 	Assert(parse->setOperations == NULL);
 	parse->havingQual = pullup_replace_vars(parse->havingQual, rvcontext);
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
new file mode 100644
index 7698bfa..931b9c0
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -134,6 +134,7 @@ preprocess_targetlist(PlannerInfo *root)
 	if (command_type == CMD_MERGE)
 	{
 		ListCell   *l;
+		List	   *vars;
 
 		/*
 		 * For MERGE, handle targetlist of each MergeAction separately. Give
@@ -144,7 +145,6 @@ preprocess_targetlist(PlannerInfo *root)
 		foreach(l, parse->mergeActionList)
 		{
 			MergeAction *action = (MergeAction *) lfirst(l);
-			List	   *vars;
 			ListCell   *l2;
 
 			if (action->commandType == CMD_INSERT)
@@ -182,6 +182,30 @@ preprocess_targetlist(PlannerInfo *root)
 			}
 			list_free(vars);
 		}
+
+		/*
+		 * Add resjunk entries for any Vars and PlaceHolderVars used in the
+		 * join condition that belong to relations other than the target.  We
+		 * don't expect to see any aggregates or window functions here.
+		 */
+		vars = pull_var_clause(parse->mergeJoinCondition,
+							   PVC_INCLUDE_PLACEHOLDERS);
+		foreach(l, vars)
+		{
+			Var		   *var = (Var *) lfirst(l);
+			TargetEntry *tle;
+
+			if (IsA(var, Var) && var->varno == result_relation)
+				continue;		/* don't need it */
+
+			if (tlist_member((Expr *) var, tlist))
+				continue;		/* already got it */
+
+			tle = makeTargetEntry((Expr *) var,
+								  list_length(tlist) + 1,
+								  NULL, true);
+			tlist = lappend(tlist, tle);
+		}
 	}
 
 	/*
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
new file mode 100644
index 246cd8f..e73b883
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -3702,6 +3702,7 @@ create_lockrows_path(PlannerInfo *root,
  * 'onconflict' is the ON CONFLICT clause, or NULL
  * 'epqParam' is the ID of Param for EvalPlanQual re-eval
  * 'mergeActionLists' is a list of lists of MERGE actions (one per rel)
+ * 'mergeJoinConditions' is a list of join conditions for MERGE (one per rel)
  */
 ModifyTablePath *
 create_modifytable_path(PlannerInfo *root, RelOptInfo *rel,
@@ -3713,7 +3714,8 @@ create_modifytable_path(PlannerInfo *roo
 						List *updateColnosLists,
 						List *withCheckOptionLists, List *returningLists,
 						List *rowMarks, OnConflictExpr *onconflict,
-						List *mergeActionLists, int epqParam)
+						List *mergeActionLists, List *mergeJoinConditions,
+						int epqParam)
 {
 	ModifyTablePath *pathnode = makeNode(ModifyTablePath);
 
@@ -3781,6 +3783,7 @@ create_modifytable_path(PlannerInfo *roo
 	pathnode->onconflict = onconflict;
 	pathnode->epqParam = epqParam;
 	pathnode->mergeActionLists = mergeActionLists;
+	pathnode->mergeJoinConditions = mergeJoinConditions;
 
 	return pathnode;
 }
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index c6e2f67..1cd1f21
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -275,6 +275,7 @@ static Node *makeRecursiveViewSelect(cha
 	struct SelectLimit *selectlimit;
 	SetQuantifier setquantifier;
 	struct GroupClause *groupclause;
+	MergeMatchKind mergematch;
 	MergeWhenClause *mergewhen;
 	struct KeyActions *keyactions;
 	struct KeyAction *keyaction;
@@ -516,6 +517,7 @@ static Node *makeRecursiveViewSelect(cha
 %type <onconflict> opt_on_conflict
 %type <mergewhen>	merge_insert merge_update merge_delete
 
+%type <mergematch> merge_when_tgt_matched merge_when_tgt_not_matched
 %type <node>	merge_when_clause opt_merge_when_condition
 %type <list>	merge_when_list
 
@@ -760,11 +762,11 @@ static Node *makeRecursiveViewSelect(cha
 	SAVEPOINT SCALAR SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT
 	SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
-	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
+	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SOURCE SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRIP_P
 	SUBSCRIPTION SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
 
-	TABLE TABLES TABLESAMPLE TABLESPACE TEMP TEMPLATE TEMPORARY TEXT_P THEN
+	TABLE TABLES TABLESAMPLE TABLESPACE TARGET TEMP TEMPLATE TEMPORARY TEXT_P THEN
 	TIES TIME TIMESTAMP TO TRAILING TRANSACTION TRANSFORM
 	TREAT TRIGGER TRIM TRUE_P
 	TRUNCATE TRUSTED TYPE_P TYPES_P
@@ -12392,50 +12394,66 @@ merge_when_list:
 			| merge_when_list merge_when_clause		{ $$ = lappend($1,$2); }
 		;
 
+/*
+ * A WHEN clause may be WHEN MATCHED, WHEN NOT MATCHED BY SOURCE, or WHEN NOT
+ * MATCHED [BY TARGET]. The first two cases match target tuples, and support
+ * UPDATE/DELETE/DO NOTHING actions. The third case does not match target
+ * tuples, and only supports INSERT/DO NOTHING actions.
+ */
 merge_when_clause:
-			WHEN MATCHED opt_merge_when_condition THEN merge_update
+			merge_when_tgt_matched opt_merge_when_condition THEN merge_update
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN merge_delete
+			| merge_when_tgt_matched opt_merge_when_condition THEN merge_delete
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN merge_insert
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN merge_insert
 				{
-					$6->matched = false;
-					$6->condition = $4;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $6;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = true;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $3;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = false;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $4;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
 		;
 
+merge_when_tgt_matched:
+			WHEN MATCHED					{ $$ = MERGE_WHEN_MATCHED; }
+			| WHEN NOT MATCHED BY SOURCE	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_SOURCE; }
+		;
+
+merge_when_tgt_not_matched:
+			WHEN NOT MATCHED				{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+			| WHEN NOT MATCHED BY TARGET	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+		;
+
 opt_merge_when_condition:
 			AND a_expr				{ $$ = $2; }
 			|						{ $$ = NULL; }
@@ -17394,6 +17412,7 @@ unreserved_keyword:
 			| SIMPLE
 			| SKIP
 			| SNAPSHOT
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -17412,6 +17431,7 @@ unreserved_keyword:
 			| SYSTEM_P
 			| TABLES
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
@@ -18007,6 +18027,7 @@ bare_label_keyword:
 			| SMALLINT
 			| SNAPSHOT
 			| SOME
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -18030,6 +18051,7 @@ bare_label_keyword:
 			| TABLES
 			| TABLESAMPLE
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
diff --git a/src/backend/parser/parse_merge.c b/src/backend/parser/parse_merge.c
new file mode 100644
index a7d8ba7..272cef5
--- a/src/backend/parser/parse_merge.c
+++ b/src/backend/parser/parse_merge.c
@@ -40,9 +40,9 @@ static void setNamespaceVisibilityForRTE
  * Make appropriate changes to the namespace visibility while transforming
  * individual action's quals and targetlist expressions. In particular, for
  * INSERT actions we must only see the source relation (since INSERT action is
- * invoked for NOT MATCHED tuples and hence there is no target tuple to deal
- * with). On the other hand, UPDATE and DELETE actions can see both source and
- * target relations.
+ * invoked for NOT MATCHED [BY TARGET] tuples and hence there is no target
+ * tuple to deal with). On the other hand, UPDATE and DELETE actions can see
+ * both source and target relations, unless invoked for NOT MATCHED BY SOURCE.
  *
  * Also, since the internal join node can hide the source and target
  * relations, we must explicitly make the respective relation as visible so
@@ -58,7 +58,7 @@ setNamespaceForMergeWhen(ParseState *pst
 	targetRelRTE = rt_fetch(targetRTI, pstate->p_rtable);
 	sourceRelRTE = rt_fetch(sourceRTI, pstate->p_rtable);
 
-	if (mergeWhenClause->matched)
+	if (mergeWhenClause->matchKind == MERGE_WHEN_MATCHED)
 	{
 		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
 			   mergeWhenClause->commandType == CMD_DELETE ||
@@ -70,11 +70,25 @@ setNamespaceForMergeWhen(ParseState *pst
 		setNamespaceVisibilityForRTE(pstate->p_namespace,
 									 sourceRelRTE, true, true);
 	}
-	else
+	else if (mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
 	{
 		/*
-		 * NOT MATCHED actions can't see target relation, but they can see
-		 * source relation.
+		 * NOT MATCHED BY SOURCE actions can see the target relation, but they
+		 * can't see the source relation.
+		 */
+		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
+			   mergeWhenClause->commandType == CMD_DELETE ||
+			   mergeWhenClause->commandType == CMD_NOTHING);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 targetRelRTE, true, true);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 sourceRelRTE, false, false);
+	}
+	else						/* MERGE_WHEN_NOT_MATCHED_BY_TARGET */
+	{
+		/*
+		 * NOT MATCHED [BY TARGET] actions can't see target relation, but they
+		 * can see source relation.
 		 */
 		Assert(mergeWhenClause->commandType == CMD_INSERT ||
 			   mergeWhenClause->commandType == CMD_NOTHING);
@@ -95,10 +109,9 @@ transformMergeStmt(ParseState *pstate, M
 	Query	   *qry = makeNode(Query);
 	ListCell   *l;
 	AclMode		targetPerms = ACL_NO_RIGHTS;
-	bool		is_terminal[2];
+	bool		is_terminal[3];
 	Index		sourceRTI;
 	List	   *mergeActionList;
-	Node	   *joinExpr;
 	ParseNamespaceItem *nsitem;
 
 	/* There can't be any outer WITH to worry about */
@@ -122,12 +135,12 @@ transformMergeStmt(ParseState *pstate, M
 	/*
 	 * Check WHEN clauses for permissions and sanity
 	 */
-	is_terminal[0] = false;
-	is_terminal[1] = false;
+	is_terminal[MERGE_WHEN_MATCHED] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
 	foreach(l, stmt->mergeWhenClauses)
 	{
 		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
-		int			when_type = (mergeWhenClause->matched ? 0 : 1);
 
 		/*
 		 * Collect permissions to check, according to action types. We require
@@ -157,12 +170,12 @@ transformMergeStmt(ParseState *pstate, M
 		/*
 		 * Check for unreachable WHEN clauses
 		 */
-		if (is_terminal[when_type])
+		if (is_terminal[mergeWhenClause->matchKind])
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
 					 errmsg("unreachable WHEN clause specified after unconditional WHEN clause")));
 		if (mergeWhenClause->condition == NULL)
-			is_terminal[when_type] = true;
+			is_terminal[mergeWhenClause->matchKind] = true;
 	}
 
 	/*
@@ -223,16 +236,15 @@ transformMergeStmt(ParseState *pstate, M
 	 * side, so add that to the namespace.
 	 */
 	addNSItemToQuery(pstate, pstate->p_target_nsitem, false, true, true);
-	joinExpr = transformExpr(pstate, stmt->joinCondition,
-							 EXPR_KIND_JOIN_ON);
+	qry->mergeJoinCondition = transformExpr(pstate, stmt->joinCondition,
+											EXPR_KIND_JOIN_ON);
 
 	/*
 	 * Create the temporary query's jointree using the joinlist we built using
-	 * just the source relation; the target relation is not included.  The
-	 * quals we use are the join conditions to the merge target.  The join
+	 * just the source relation; the target relation is not included. The join
 	 * will be constructed fully by transform_MERGE_to_join.
 	 */
-	qry->jointree = makeFromExpr(pstate->p_joinlist, joinExpr);
+	qry->jointree = makeFromExpr(pstate->p_joinlist, NULL);
 
 	/*
 	 * We now have a good query shape, so now look at the WHEN conditions and
@@ -256,11 +268,7 @@ transformMergeStmt(ParseState *pstate, M
 
 		action = makeNode(MergeAction);
 		action->commandType = mergeWhenClause->commandType;
-		action->matched = mergeWhenClause->matched;
-
-		/* Use an outer join if any INSERT actions exist in the command. */
-		if (action->commandType == CMD_INSERT)
-			qry->mergeUseOuterJoin = true;
+		action->matchKind = mergeWhenClause->matchKind;
 
 		/*
 		 * Set namespace for the specific action. This must be done before
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
new file mode 100644
index 2a1ee69..3c64273
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -7090,6 +7090,7 @@ get_merge_query_def(Query *query, depars
 	StringInfo	buf = context->buf;
 	RangeTblEntry *rte;
 	ListCell   *lc;
+	bool		haveNotMatchedBySource;
 
 	/* Insert the WITH clause if given */
 	get_with_clause(query, context);
@@ -7115,7 +7116,26 @@ get_merge_query_def(Query *query, depars
 	get_from_clause(query, " USING ", context);
 	appendContextKeyword(context, " ON ",
 						 -PRETTYINDENT_STD, PRETTYINDENT_STD, 2);
-	get_rule_expr(query->jointree->quals, context, false);
+	get_rule_expr(query->mergeJoinCondition, context, false);
+
+	/*
+	 * Test for any NOT MATCHED BY SOURCE actions.  If there are none, then
+	 * any NOT MATCHED BY TARGET actions are output as "WHEN NOT MATCHED", per
+	 * SQL standard.  Otherwise, we have a non-SQL-standard query, so output
+	 * "BY SOURCE" / "BY TARGET" qualifiers for all NOT MATCHED actions, to be
+	 * more explicit.
+	 */
+	haveNotMatchedBySource = false;
+	foreach(lc, query->mergeActionList)
+	{
+		MergeAction *action = lfirst_node(MergeAction, lc);
+
+		if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+		{
+			haveNotMatchedBySource = true;
+			break;
+		}
+	}
 
 	/* Print each merge action */
 	foreach(lc, query->mergeActionList)
@@ -7124,7 +7144,24 @@ get_merge_query_def(Query *query, depars
 
 		appendContextKeyword(context, " WHEN ",
 							 -PRETTYINDENT_STD, PRETTYINDENT_STD, 2);
-		appendStringInfo(buf, "%sMATCHED", action->matched ? "" : "NOT ");
+		switch (action->matchKind)
+		{
+			case MERGE_WHEN_MATCHED:
+				appendStringInfo(buf, "MATCHED");
+				break;
+			case MERGE_WHEN_NOT_MATCHED_BY_SOURCE:
+				appendStringInfo(buf, "NOT MATCHED BY SOURCE");
+				break;
+			case MERGE_WHEN_NOT_MATCHED_BY_TARGET:
+				if (haveNotMatchedBySource)
+					appendStringInfo(buf, "NOT MATCHED BY TARGET");
+				else
+					appendStringInfo(buf, "NOT MATCHED");
+				break;
+			default:
+				elog(ERROR, "unrecognized matchKind: %d",
+					 (int) action->matchKind);
+		}
 
 		if (action->qual)
 		{
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
new file mode 100644
index 73133ce..ed2cb19
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -4333,17 +4333,35 @@ psql_completion(const char *text, int st
 			 TailMatches("USING", MatchAny, MatchAny, "ON", MatchAny, MatchAny, MatchAny, "WHEN"))
 		COMPLETE_WITH("MATCHED", "NOT MATCHED");
 
-	/* Complete ... WHEN [NOT] MATCHED with THEN/AND */
+	/*
+	 * Complete ... WHEN MATCHED and WHEN NOT MATCHED BY SOURCE|TARGET with
+	 * THEN/AND
+	 */
 	else if (TailMatches("WHEN", "MATCHED") ||
-			 TailMatches("WHEN", "NOT", "MATCHED"))
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE|TARGET"))
 		COMPLETE_WITH("THEN", "AND");
 
-	/* Complete ... WHEN MATCHED THEN with UPDATE SET/DELETE/DO NOTHING */
-	else if (TailMatches("WHEN", "MATCHED", "THEN"))
+	/* Complete ... WHEN NOT MATCHED with BY/THEN/AND */
+	else if (TailMatches("WHEN", "NOT", "MATCHED"))
+		COMPLETE_WITH("BY", "THEN", "AND");
+
+	/* Complete ... WHEN NOT MATCHED BY with SOURCE/TARGET */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "BY"))
+		COMPLETE_WITH("SOURCE", "TARGET");
+
+	/*
+	 * Complete ... WHEN MATCHED THEN and WHEN NOT MATCHED BY SOURCE THEN with
+	 * UPDATE SET/DELETE/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE", "THEN"))
 		COMPLETE_WITH("UPDATE SET", "DELETE", "DO NOTHING");
 
-	/* Complete ... WHEN NOT MATCHED THEN with INSERT/DO NOTHING */
-	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN"))
+	/*
+	 * Complete ... WHEN NOT MATCHED [BY TARGET] THEN with INSERT/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "TARGET", "THEN"))
 		COMPLETE_WITH("INSERT", "DO NOTHING");
 
 /* NOTIFY --- can be inside EXPLAIN, RULE, etc */
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
new file mode 100644
index 444a5f0..9f65cfb
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -544,9 +544,11 @@ typedef struct ResultRelInfo
 	/* ON CONFLICT evaluation state */
 	OnConflictSetState *ri_onConflict;
 
-	/* for MERGE, lists of MergeActionState */
-	List	   *ri_matchedMergeAction;
-	List	   *ri_notMatchedMergeAction;
+	/* for MERGE, lists of MergeActionState (one per MergeMatchKind) */
+	List	   *ri_MergeActions[3];
+
+	/* for MERGE, join condition-checking expr state */
+	ExprState  *ri_MergeJoinCondition;
 
 	/* partition check expression state (NULL if not set up yet) */
 	ExprState  *ri_PartitionCheckExpr;
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
new file mode 100644
index 2380821..7c553a6
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -175,8 +175,6 @@ typedef struct Query
 								 * also USING clause for MERGE */
 
 	List	   *mergeActionList;	/* list of actions for MERGE (only) */
-	/* whether to use outer join */
-	bool		mergeUseOuterJoin pg_node_attr(query_jumble_ignore);
 
 	/*
 	 * rtable index of target relation for MERGE to pull data. Initially, this
@@ -186,6 +184,9 @@ typedef struct Query
 	 */
 	int			mergeTargetRelation pg_node_attr(query_jumble_ignore);
 
+	/* join condition between source and target for MERGE */
+	Node	   *mergeJoinCondition;
+
 	List	   *targetList;		/* target list (of TargetEntry) */
 
 	/* OVERRIDING clause */
@@ -1676,7 +1677,7 @@ typedef struct CommonTableExpr
 typedef struct MergeWhenClause
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *condition;		/* WHEN conditions (raw parser) */
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
new file mode 100644
index 534692b..5ccfa5f
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -2367,6 +2367,8 @@ typedef struct ModifyTablePath
 	int			epqParam;		/* ID of Param for EvalPlanQual re-eval */
 	List	   *mergeActionLists;	/* per-target-table lists of actions for
 									 * MERGE */
+	List	   *mergeJoinConditions;	/* per-target-table join conditions
+										 * for MERGE */
 } ModifyTablePath;
 
 /*
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
new file mode 100644
index b4ef6bc..ebefd65
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -251,6 +251,8 @@ typedef struct ModifyTable
 	List	   *exclRelTlist;	/* tlist of the EXCLUDED pseudo relation */
 	List	   *mergeActionLists;	/* per-target-table lists of actions for
 									 * MERGE */
+	List	   *mergeJoinConditions;	/* per-target-table join conditions
+										 * for MERGE */
 } ModifyTable;
 
 struct PartitionPruneInfo;		/* forward reference to struct below */
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
new file mode 100644
index 4a15460..f7eebd8
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -1732,10 +1732,18 @@ typedef struct BooleanTest
  *
  * Transformed representation of a WHEN clause in a MERGE statement
  */
+
+typedef enum MergeMatchKind
+{
+	MERGE_WHEN_MATCHED,
+	MERGE_WHEN_NOT_MATCHED_BY_SOURCE,
+	MERGE_WHEN_NOT_MATCHED_BY_TARGET
+} MergeMatchKind;
+
 typedef struct MergeAction
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	/* OVERRIDING clause */
 	OverridingKind override pg_node_attr(query_jumble_ignore);
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
new file mode 100644
index c43d97b..1b3dd52
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -283,7 +283,8 @@ extern ModifyTablePath *create_modifytab
 												List *updateColnosLists,
 												List *withCheckOptionLists, List *returningLists,
 												List *rowMarks, OnConflictExpr *onconflict,
-												List *mergeActionLists, int epqParam);
+												List *mergeActionLists, List *mergeJoinConditions,
+												int epqParam);
 extern LimitPath *create_limit_path(PlannerInfo *root, RelOptInfo *rel,
 									Path *subpath,
 									Node *limitOffset, Node *limitCount,
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
new file mode 100644
index 2331aca..b7d5515
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -403,6 +403,7 @@ PG_KEYWORD("skip", SKIP, UNRESERVED_KEYW
 PG_KEYWORD("smallint", SMALLINT, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("snapshot", SNAPSHOT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("some", SOME, RESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("source", SOURCE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("sql", SQL_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("stable", STABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("standalone", STANDALONE_P, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -426,6 +427,7 @@ PG_KEYWORD("table", TABLE, RESERVED_KEYW
 PG_KEYWORD("tables", TABLES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablesample", TABLESAMPLE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablespace", TABLESPACE, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("target", TARGET, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temp", TEMP, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("template", TEMPLATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temporary", TEMPORARY, UNRESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/test/isolation/expected/merge-update.out b/src/test/isolation/expected/merge-update.out
new file mode 100644
index f5f7e3b..fe3689f
--- a/src/test/isolation/expected/merge-update.out
+++ b/src/test/isolation/expected/merge-update.out
@@ -37,13 +37,15 @@ step merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a';
 
 step select2: SELECT * FROM target;
-key|val                     
----+------------------------
-  2|setup1 updated by merge1
-  1|merge2a                 
+key|val                                                   
+---+------------------------------------------------------
+  3|setup1 updated by merge1 source not matched by merge2a
+  1|merge2a                                               
 (2 rows)
 
 step c2: COMMIT;
@@ -86,15 +88,17 @@ step merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a';
  <waiting ...>
 step c1: COMMIT;
 step merge2a: <... completed>
 step select2: SELECT * FROM target;
-key|val                     
----+------------------------
-  2|setup1 updated by merge1
-  1|merge2a                 
+key|val                                                   
+---+------------------------------------------------------
+  3|setup1 updated by merge1 source not matched by merge2a
+  1|merge2a                                               
 (2 rows)
 
 step c2: COMMIT;
@@ -116,7 +120,9 @@ step merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a';
  <waiting ...>
 step a1: ABORT;
 step merge2a: <... completed>
@@ -205,15 +211,17 @@ step pa_merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a';
  <waiting ...>
 step c1: COMMIT;
 step pa_merge2a: <... completed>
 step pa_select2: SELECT * FROM pa_target;
 key|val                                               
 ---+--------------------------------------------------
-  2|initial                                           
   2|initial updated by pa_merge1 updated by pa_merge2a
+  3|initial source not matched by pa_merge2a          
 (2 rows)
 
 step c2: COMMIT;
@@ -235,7 +243,9 @@ step pa_merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a';
  <waiting ...>
 step c1: COMMIT;
 step pa_merge2a: <... completed>
@@ -262,14 +272,16 @@ step pa_merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a';
 
 step pa_select2: SELECT * FROM pa_target;
-key|val                         
----+----------------------------
-  1|pa_merge2a                  
-  2|initial                     
-  2|initial updated by pa_merge2
+key|val                                                          
+---+-------------------------------------------------------------
+  1|pa_merge2a                                                   
+  3|initial source not matched by pa_merge2a                     
+  3|initial updated by pa_merge2 source not matched by pa_merge2a
 (3 rows)
 
 step c2: COMMIT;
diff --git a/src/test/isolation/specs/merge-update.spec b/src/test/isolation/specs/merge-update.spec
new file mode 100644
index 3ccd466..657b4ac
--- a/src/test/isolation/specs/merge-update.spec
+++ b/src/test/isolation/specs/merge-update.spec
@@ -92,7 +92,9 @@ step "merge2a"
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a';
 }
 step "merge2b"
 {
@@ -122,7 +124,9 @@ step "pa_merge2a"
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a';
 }
 # MERGE proceeds only if 'val' unchanged
 step "pa_merge2b_when"
diff --git a/src/test/regress/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index e3ebf46..17c0cba
--- a/src/test/regress/expected/merge.out
+++ b/src/test/regress/expected/merge.out
@@ -72,6 +72,15 @@ WHEN MATCHED THEN
 ERROR:  syntax error at or near "INSERT"
 LINE 5:  INSERT DEFAULT VALUES;
          ^
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
+ERROR:  syntax error at or near "INSERT"
+LINE 5:  INSERT DEFAULT VALUES;
+         ^
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -108,6 +117,15 @@ WHEN NOT MATCHED THEN
 ERROR:  syntax error at or near "UPDATE"
 LINE 5:  UPDATE SET balance = 0;
          ^
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
+ERROR:  syntax error at or near "UPDATE"
+LINE 5:  UPDATE SET balance = 0;
+         ^
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -270,6 +288,22 @@ SELECT * FROM target ORDER BY tid;
 (4 rows)
 
 ROLLBACK;
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   4 |      40
+(1 row)
+
+ROLLBACK;
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -737,6 +771,19 @@ SELECT * FROM wq_target;
    1 |      -1
 (1 row)
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+ERROR:  invalid reference to FROM-clause entry for table "s"
+LINE 3: WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+                                       ^
+DETAIL:  There is an entry for table "s", but it cannot be referenced from this part of the query.
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
  balance | sid 
@@ -922,6 +969,45 @@ SELECT * FROM target ORDER BY tid;
 (3 rows)
 
 ROLLBACK;
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE DELETE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  BEFORE INSERT ROW trigger row: (4,40)
+NOTICE:  BEFORE DELETE ROW trigger row: (2,20)
+NOTICE:  BEFORE UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  AFTER INSERT ROW trigger row: (4,40)
+NOTICE:  AFTER DELETE ROW trigger row: (2,20)
+NOTICE:  AFTER UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER DELETE STATEMENT trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |       0
+   3 |      10
+   4 |      40
+(3 rows)
+
+ROLLBACK;
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -1450,6 +1536,50 @@ WHEN NOT MATCHED AND s.a < 20 THEN
                ->  Seq Scan on ex_mtarget t (actual rows=49 loops=1)
 (12 rows)
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=54
+   ->  Merge Left Join (actual rows=54 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=100
+   ->  Merge Full Join (actual rows=100 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
@@ -1529,7 +1659,7 @@ CREATE TABLE pa_source (sid integer, del
 -- insert many rows to the source table
 INSERT INTO pa_source SELECT id, id * 10  FROM generate_series(1,14) AS id;
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 -- try simple MERGE
 BEGIN;
 MERGE INTO pa_target t
@@ -1538,10 +1668,12 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
    3 |     330 | initial updated by merge
@@ -1556,7 +1688,8 @@ SELECT * FROM pa_target ORDER BY tid;
   12 |     120 | inserted by merge
   13 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+  15 |    1500 | initial not matched by source
+(15 rows)
 
 ROLLBACK;
 -- same with a constant qual
@@ -1567,31 +1700,34 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
+   3 |     300 | initial not matched by source
    3 |      30 | inserted by merge
-   3 |     300 | initial
    4 |      40 | inserted by merge
-   5 |     500 | initial
+   5 |     500 | initial not matched by source
    5 |      50 | inserted by merge
    6 |      60 | inserted by merge
-   7 |     700 | initial
+   7 |     700 | initial not matched by source
    7 |      70 | inserted by merge
    8 |      80 | inserted by merge
+   9 |     900 | initial not matched by source
    9 |      90 | inserted by merge
-   9 |     900 | initial
   10 |     100 | inserted by merge
-  11 |    1100 | initial
+  11 |    1100 | initial not matched by source
   11 |     110 | inserted by merge
   12 |     120 | inserted by merge
-  13 |    1300 | initial
+  13 |    1300 | initial not matched by source
   13 |     130 | inserted by merge
   14 |     140 | inserted by merge
-(20 rows)
+  15 |    1500 | initial not matched by source
+(21 rows)
 
 ROLLBACK;
 -- try updating the partition key column
@@ -1606,7 +1742,9 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 IF FOUND THEN
   GET DIAGNOSTICS result := ROW_COUNT;
 END IF;
@@ -1616,27 +1754,28 @@ $$;
 SELECT merge_func();
  merge_func 
 ------------
-         14
+         15
 (1 row)
 
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
+   1 |    1500 | initial not matched by source
    2 |     110 | initial updated by merge
    2 |      20 | inserted by merge
-   4 |      40 | inserted by merge
    4 |     330 | initial updated by merge
+   4 |      40 | inserted by merge
    6 |     550 | initial updated by merge
    6 |      60 | inserted by merge
-   8 |      80 | inserted by merge
    8 |     770 | initial updated by merge
+   8 |      80 | inserted by merge
   10 |     990 | initial updated by merge
   10 |     100 | inserted by merge
   12 |    1210 | initial updated by merge
   12 |     120 | inserted by merge
   14 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+(15 rows)
 
 ROLLBACK;
 DROP TABLE pa_target CASCADE;
@@ -1658,7 +1797,7 @@ ALTER TABLE pa_target ATTACH PARTITION p
 ALTER TABLE pa_target ATTACH PARTITION part3 FOR VALUES IN (3,8,9);
 ALTER TABLE pa_target ATTACH PARTITION part4 DEFAULT;
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 -- try simple MERGE
 BEGIN;
 DO $$
@@ -1671,15 +1810,17 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 14
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 15
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
    3 |     330 | initial updated by merge
@@ -1694,7 +1835,8 @@ SELECT * FROM pa_target ORDER BY tid;
   12 |     120 | inserted by merge
   13 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+  15 |    1500 | initial not matched by source
+(15 rows)
 
 ROLLBACK;
 -- same with a constant qual
@@ -1706,29 +1848,32 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
+   3 |     300 | initial not matched by source
    3 |      30 | inserted by merge
-   3 |     300 | initial
    4 |      40 | inserted by merge
    6 |      60 | inserted by merge
-   7 |     700 | initial
+   7 |     700 | initial not matched by source
    7 |      70 | inserted by merge
    8 |      80 | inserted by merge
-   9 |     900 | initial
+   9 |     900 | initial not matched by source
    9 |      90 | inserted by merge
   10 |     100 | inserted by merge
+  11 |    1100 | initial not matched by source
   11 |     110 | inserted by merge
-  11 |    1100 | initial
   12 |     120 | inserted by merge
-  13 |    1300 | initial
+  13 |    1300 | initial not matched by source
   13 |     130 | inserted by merge
   14 |     140 | inserted by merge
-(18 rows)
+  15 |    1500 | initial not matched by source
+(19 rows)
 
 ROLLBACK;
 -- try updating the partition key column
@@ -1743,30 +1888,33 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 14
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 15
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
+   1 |    1500 | initial not matched by source
    2 |     110 | initial updated by merge
    2 |      20 | inserted by merge
-   4 |      40 | inserted by merge
    4 |     330 | initial updated by merge
+   4 |      40 | inserted by merge
    6 |     550 | initial updated by merge
    6 |      60 | inserted by merge
-   8 |      80 | inserted by merge
    8 |     770 | initial updated by merge
+   8 |      80 | inserted by merge
   10 |     990 | initial updated by merge
   10 |     100 | inserted by merge
   12 |    1210 | initial updated by merge
   12 |     120 | inserted by merge
   14 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+(15 rows)
 
 ROLLBACK;
 -- as above, but blocked by BEFORE DELETE ROW trigger
@@ -1785,15 +1933,17 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 10
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 11
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     100 | initial
    2 |      20 | inserted by merge
    3 |     300 | initial
@@ -1808,7 +1958,8 @@ SELECT * FROM pa_target ORDER BY tid;
   12 |     120 | inserted by merge
   14 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+  15 |    1500 | initial not matched by source
+(15 rows)
 
 ROLLBACK;
 -- as above, but blocked by BEFORE INSERT ROW trigger
@@ -1827,19 +1978,22 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 3
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 4
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    6 |     550 | initial updated by merge
   12 |    1210 | initial updated by merge
   14 |    1430 | initial updated by merge
-(3 rows)
+  15 |    1500 | initial not matched by source
+(4 rows)
 
 ROLLBACK;
 -- test RLS enforcement
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
new file mode 100644
index 0cd2c64..4e45941
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -3718,7 +3718,39 @@ BEGIN ATOMIC
      THEN INSERT (filling[1], id)
       VALUES (s.a, s.a);
 END
+CREATE FUNCTION merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+   USING rule_merge1 s
+   ON (s.a = t.id)
+WHEN NOT MATCHED
+   THEN INSERT (data, id)
+   VALUES (s.a, s.a)
+WHEN MATCHED
+   THEN UPDATE SET data = s.b
+WHEN NOT MATCHED BY SOURCE
+   THEN DELETE;
+END;
+\sf merge_sf_test2
+CREATE OR REPLACE FUNCTION public.merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+    USING rule_merge1 s
+    ON (s.a = t.id)
+    WHEN NOT MATCHED BY TARGET
+     THEN INSERT (data, id)
+      VALUES (s.a, s.a)
+    WHEN MATCHED
+     THEN UPDATE SET data = s.b
+    WHEN NOT MATCHED BY SOURCE
+     THEN DELETE;
+END
 DROP FUNCTION merge_sf_test;
+DROP FUNCTION merge_sf_test2;
 DROP TABLE sf_target;
 --
 -- Test enabling/disabling
diff --git a/src/test/regress/expected/updatable_views.out b/src/test/regress/expected/updatable_views.out
new file mode 100644
index 794cf9c..3a43cce
--- a/src/test/regress/expected/updatable_views.out
+++ b/src/test/regress/expected/updatable_views.out
@@ -491,6 +491,23 @@ SELECT * FROM base_tbl ORDER BY a;
   5 | Unspecified
 (6 rows)
 
+MERGE INTO rw_view1 t
+  USING (VALUES (0, 'R0'), (1, 'R1'),
+                (2, 'R2'), (3, 'R3')) AS v(a,b) ON t.a = v.a
+  WHEN MATCHED AND t.a <= 1 THEN UPDATE SET b = v.b
+  WHEN MATCHED THEN DELETE
+  WHEN NOT MATCHED BY SOURCE THEN DELETE
+  WHEN NOT MATCHED AND a > 0 THEN INSERT (a) VALUES (v.a);
+SELECT * FROM base_tbl ORDER BY a;
+ a  |      b      
+----+-------------
+ -2 | Row -2
+ -1 | Row -1
+  0 | Row 0
+  1 | R1
+  3 | Unspecified
+(5 rows)
+
 EXPLAIN (costs off) UPDATE rw_view1 SET a=6 WHERE a=5;
                     QUERY PLAN                    
 --------------------------------------------------
@@ -537,6 +554,23 @@ MERGE INTO rw_view1 t
 EXPLAIN (costs off)
 MERGE INTO rw_view1 t
   USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
+  WHEN NOT MATCHED BY SOURCE THEN DELETE;
+                            QUERY PLAN                             
+-------------------------------------------------------------------
+ Merge on base_tbl
+   ->  Hash Left Join
+         Hash Cond: (base_tbl.a = generate_series.generate_series)
+         ->  Bitmap Heap Scan on base_tbl
+               Recheck Cond: (a > 0)
+               ->  Bitmap Index Scan on base_tbl_pkey
+                     Index Cond: (a > 0)
+         ->  Hash
+               ->  Function Scan on generate_series
+(9 rows)
+
+EXPLAIN (costs off)
+MERGE INTO rw_view1 t
+  USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
   WHEN NOT MATCHED THEN INSERT (a) VALUES (s.a);
                             QUERY PLAN                             
 -------------------------------------------------------------------
@@ -640,6 +674,20 @@ SELECT * FROM rw_view2 ORDER BY aaa;
    5 | Unspecified
 (3 rows)
 
+MERGE INTO rw_view2 t
+  USING (VALUES (4, 'r4'), (5, 'r5'), (6, 'r6')) AS v(a,b) ON aaa = v.a
+  WHEN MATCHED AND aaa = 4 THEN DELETE
+  WHEN MATCHED THEN UPDATE SET bbb = v.b
+  WHEN NOT MATCHED THEN INSERT (aaa) VALUES (v.a)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET bbb = 'Not matched by source';
+SELECT * FROM rw_view2 ORDER BY aaa;
+ aaa |          bbb          
+-----+-----------------------
+   1 | Not matched by source
+   5 | r5
+   6 | Unspecified
+(3 rows)
+
 EXPLAIN (costs off) UPDATE rw_view2 SET aaa=5 WHERE aaa=4;
                        QUERY PLAN                       
 --------------------------------------------------------
@@ -1082,6 +1130,22 @@ SELECT * FROM base_tbl ORDER BY a;
   3 | R3
 (5 rows)
 
+MERGE INTO rw_view2 t
+  USING (SELECT x, 'r'||x FROM generate_series(0,2) x) AS s(a,b) ON t.a = s.a
+  WHEN MATCHED THEN UPDATE SET b = s.b
+  WHEN NOT MATCHED AND s.a > 0 THEN INSERT VALUES (s.a, s.b)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET b = 'Not matched by source';
+SELECT * FROM base_tbl ORDER BY a;
+ a  |           b           
+----+-----------------------
+ -2 | Row -2
+ -1 | Row -1
+  0 | Row 0
+  1 | r1
+  2 | r2
+  3 | Not matched by source
+(6 rows)
+
 EXPLAIN (costs off) UPDATE rw_view2 SET a=3 WHERE a=2;
                         QUERY PLAN                        
 ----------------------------------------------------------
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index 79a1868..a4607a8
--- a/src/test/regress/sql/merge.sql
+++ b/src/test/regress/sql/merge.sql
@@ -53,6 +53,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN MATCHED THEN
 	INSERT DEFAULT VALUES;
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -77,6 +83,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN NOT MATCHED THEN
 	UPDATE SET balance = 0;
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -214,6 +226,18 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta);
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -498,6 +522,17 @@ WHEN NOT MATCHED AND s.balance = 100 THE
 	INSERT (tid) VALUES (s.sid);
 SELECT * FROM wq_target;
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
+
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
 MERGE INTO wq_target t
@@ -625,6 +660,25 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -930,6 +984,20 @@ WHEN MATCHED AND t.a >= 30 AND t.a <= 40
 WHEN NOT MATCHED AND s.a < 20 THEN
 	INSERT VALUES (a, b)');
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
@@ -985,7 +1053,7 @@ CREATE TABLE pa_source (sid integer, del
 -- insert many rows to the source table
 INSERT INTO pa_source SELECT id, id * 10  FROM generate_series(1,14) AS id;
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 
 -- try simple MERGE
 BEGIN;
@@ -995,8 +1063,10 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- same with a constant qual
@@ -1007,8 +1077,10 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- try updating the partition key column
@@ -1023,7 +1095,9 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 IF FOUND THEN
   GET DIAGNOSTICS result := ROW_COUNT;
 END IF;
@@ -1031,7 +1105,7 @@ RETURN result;
 END;
 $$;
 SELECT merge_func();
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 DROP TABLE pa_target CASCADE;
@@ -1057,7 +1131,7 @@ ALTER TABLE pa_target ATTACH PARTITION p
 ALTER TABLE pa_target ATTACH PARTITION part4 DEFAULT;
 
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 
 -- try simple MERGE
 BEGIN;
@@ -1071,12 +1145,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- same with a constant qual
@@ -1088,8 +1164,10 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- try updating the partition key column
@@ -1104,12 +1182,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- as above, but blocked by BEFORE DELETE ROW trigger
@@ -1128,12 +1208,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- as above, but blocked by BEFORE INSERT ROW trigger
@@ -1152,12 +1234,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- test RLS enforcement
diff --git a/src/test/regress/sql/rules.sql b/src/test/regress/sql/rules.sql
new file mode 100644
index 6924012..198b4cd
--- a/src/test/regress/sql/rules.sql
+++ b/src/test/regress/sql/rules.sql
@@ -1336,7 +1336,26 @@ END;
 
 \sf merge_sf_test
 
+CREATE FUNCTION merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+   USING rule_merge1 s
+   ON (s.a = t.id)
+WHEN NOT MATCHED
+   THEN INSERT (data, id)
+   VALUES (s.a, s.a)
+WHEN MATCHED
+   THEN UPDATE SET data = s.b
+WHEN NOT MATCHED BY SOURCE
+   THEN DELETE;
+END;
+
+\sf merge_sf_test2
+
 DROP FUNCTION merge_sf_test;
+DROP FUNCTION merge_sf_test2;
 DROP TABLE sf_target;
 
 --
diff --git a/src/test/regress/sql/updatable_views.sql b/src/test/regress/sql/updatable_views.sql
new file mode 100644
index ae11e46..251eabf
--- a/src/test/regress/sql/updatable_views.sql
+++ b/src/test/regress/sql/updatable_views.sql
@@ -178,6 +178,15 @@ MERGE INTO rw_view1 t
   WHEN NOT MATCHED AND a > 0 THEN INSERT (a) VALUES (v.a);
 SELECT * FROM base_tbl ORDER BY a;
 
+MERGE INTO rw_view1 t
+  USING (VALUES (0, 'R0'), (1, 'R1'),
+                (2, 'R2'), (3, 'R3')) AS v(a,b) ON t.a = v.a
+  WHEN MATCHED AND t.a <= 1 THEN UPDATE SET b = v.b
+  WHEN MATCHED THEN DELETE
+  WHEN NOT MATCHED BY SOURCE THEN DELETE
+  WHEN NOT MATCHED AND a > 0 THEN INSERT (a) VALUES (v.a);
+SELECT * FROM base_tbl ORDER BY a;
+
 EXPLAIN (costs off) UPDATE rw_view1 SET a=6 WHERE a=5;
 EXPLAIN (costs off) DELETE FROM rw_view1 WHERE a=5;
 
@@ -193,6 +202,11 @@ MERGE INTO rw_view1 t
 EXPLAIN (costs off)
 MERGE INTO rw_view1 t
   USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
+  WHEN NOT MATCHED BY SOURCE THEN DELETE;
+
+EXPLAIN (costs off)
+MERGE INTO rw_view1 t
+  USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
   WHEN NOT MATCHED THEN INSERT (a) VALUES (s.a);
 
 -- it's still updatable if we add a DO ALSO rule
@@ -249,6 +263,14 @@ MERGE INTO rw_view2 t
   WHEN NOT MATCHED THEN INSERT (aaa) VALUES (v.a);
 SELECT * FROM rw_view2 ORDER BY aaa;
 
+MERGE INTO rw_view2 t
+  USING (VALUES (4, 'r4'), (5, 'r5'), (6, 'r6')) AS v(a,b) ON aaa = v.a
+  WHEN MATCHED AND aaa = 4 THEN DELETE
+  WHEN MATCHED THEN UPDATE SET bbb = v.b
+  WHEN NOT MATCHED THEN INSERT (aaa) VALUES (v.a)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET bbb = 'Not matched by source';
+SELECT * FROM rw_view2 ORDER BY aaa;
+
 EXPLAIN (costs off) UPDATE rw_view2 SET aaa=5 WHERE aaa=4;
 EXPLAIN (costs off) DELETE FROM rw_view2 WHERE aaa=4;
 
@@ -461,6 +483,13 @@ MERGE INTO rw_view2 t
   WHEN NOT MATCHED AND s.a > 0 THEN INSERT VALUES (s.a, s.b);
 SELECT * FROM base_tbl ORDER BY a;
 
+MERGE INTO rw_view2 t
+  USING (SELECT x, 'r'||x FROM generate_series(0,2) x) AS s(a,b) ON t.a = s.a
+  WHEN MATCHED THEN UPDATE SET b = s.b
+  WHEN NOT MATCHED AND s.a > 0 THEN INSERT VALUES (s.a, s.b)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET b = 'Not matched by source';
+SELECT * FROM base_tbl ORDER BY a;
+
 EXPLAIN (costs off) UPDATE rw_view2 SET a=3 WHERE a=2;
 EXPLAIN (costs off) DELETE FROM rw_view2 WHERE a=2;
 
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
new file mode 100644
index aa7a25b..08b72c5
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1574,6 +1574,7 @@ MergeAppendState
 MergeJoin
 MergeJoinClause
 MergeJoinState
+MergeMatchKind
 MergePath
 MergeScanSelCache
 MergeStmt

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
new file mode 100644
index f8f83d4..380d0c9
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -394,10 +394,14 @@
     conditions for each action are re-evaluated on the updated version of
     the row, starting from the first action, even if the action that had
     originally matched appears later in the list of actions.
-    On the other hand, if the row is concurrently updated or deleted so
-    that the join condition fails, then <command>MERGE</command> will
-    evaluate the condition's <literal>NOT MATCHED</literal> actions next,
-    and execute the first one that succeeds.
+    On the other hand, if the row is concurrently updated so that the join
+    condition fails, then <command>MERGE</command> will evaluate the
+    command's <literal>NOT MATCHED BY SOURCE</literal> and
+    <literal>NOT MATCHED [BY TARGET]</literal> actions next, and execute
+    the first one of each kind that succeeds.
+    If the row is concurrently deleted, then <command>MERGE</command>
+    will evaluate the command's <literal>NOT MATCHED [BY TARGET]</literal>
+    actions, and execute the first one that succeeds.
     If <command>MERGE</command> attempts an <command>INSERT</command>
     and a unique index is present and a duplicate row is concurrently
     inserted, then a uniqueness violation error is raised;
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
new file mode 100644
index 44e5ec0..16f0aa9
--- a/doc/src/sgml/ref/merge.sgml
+++ b/doc/src/sgml/ref/merge.sgml
@@ -34,7 +34,8 @@ USING <replaceable class="parameter">dat
 <phrase>and <replaceable class="parameter">when_clause</replaceable> is:</phrase>
 
 { WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
-  WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
+  WHEN NOT MATCHED BY SOURCE [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
+  WHEN NOT MATCHED [BY TARGET] [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
 
 <phrase>and <replaceable class="parameter">merge_insert</replaceable> is:</phrase>
 
@@ -73,7 +74,9 @@ DELETE
    from <replaceable class="parameter">data_source</replaceable> to
    the target table
    producing zero or more candidate change rows.  For each candidate change
-   row, the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal>
+   row, the status of <literal>MATCHED</literal>,
+   <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>
    is set just once, after which <literal>WHEN</literal> clauses are evaluated
    in the order specified.  For each candidate change row, the first clause to
    evaluate as true is executed.  No more than one <literal>WHEN</literal>
@@ -268,18 +271,40 @@ DELETE
       At least one <literal>WHEN</literal> clause is required.
      </para>
      <para>
+      The <literal>WHEN</literal> clause may specify <literal>WHEN MATCHED</literal>,
+      <literal>WHEN NOT MATCHED BY SOURCE</literal>, or
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>.
+      Note that the <acronym>SQL</acronym> standard only defines
+      <literal>WHEN MATCHED</literal> and <literal>WHEN NOT MATCHED</literal>
+      (which is defined to mean no matching target row).
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> is an extension to the
+      <acronym>SQL</acronym> standard, as is the option to append
+      <literal>BY TARGET</literal> to <literal>WHEN NOT MATCHED</literal>, to
+      make its meaning more explicit.
+     </para>
+     <para>
       If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
       and the candidate change row matches a row in the
-      target table,
-      the <literal>WHEN</literal> clause is executed if the
+      <replaceable class="parameter">data_source</replaceable> to a row in the
+      target table, the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
      </para>
      <para>
-      Conversely, if the <literal>WHEN</literal> clause specifies
-      <literal>WHEN NOT MATCHED</literal>
-      and the candidate change row does not match a row in the
-      target table,
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> and the candidate change
+      row represents a row in the target table that does not match a row in the
+      <replaceable class="parameter">data_source</replaceable>, the
+      <literal>WHEN</literal> clause is executed if the
+      <replaceable class="parameter">condition</replaceable> is
+      absent or it evaluates to <literal>true</literal>.
+     </para>
+     <para>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal> and the candidate change
+      row represents a row in the
+      <replaceable class="parameter">data_source</replaceable> that does not
+      match a row in the target table,
       the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
@@ -299,7 +324,10 @@ DELETE
      <para>
       A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
       in both the source and the target relations. A condition on a
-      <literal>WHEN NOT MATCHED</literal> clause can only refer to columns from
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> clause can only refer to
+      columns from the target relation, since by definition there is no matching
+      source row. A condition on a <literal>WHEN NOT MATCHED [BY TARGET]</literal>
+      clause can only refer to columns from
       the source relation, since by definition there is no matching target row.
       Only the system attributes from the target table are accessible.
      </para>
@@ -423,8 +451,10 @@ DELETE
       <literal>WHEN MATCHED</literal> clause, the expression can use values
       from the original row in the target table, and values from the
       <replaceable class="parameter">data_source</replaceable> row.
-      If used in a <literal>WHEN NOT MATCHED</literal> clause, the
-      expression can use values from the
+      If used in a <literal>WHEN NOT MATCHED BY SOURCE</literal> clause, the
+      expression can only use values from the original row in the target table.
+      If used in a <literal>WHEN NOT MATCHED [BY TARGET]</literal> clause, the
+      expression can only use values from the
       <replaceable class="parameter">data_source</replaceable> row.
      </para>
     </listitem>
@@ -535,8 +565,9 @@ MERGE <replaceable class="parameter">tot
        <orderedlist>
         <listitem>
          <para>
-          Evaluate whether each row is <literal>MATCHED</literal> or
-          <literal>NOT MATCHED</literal>.
+          Evaluate whether each row is <literal>MATCHED</literal>,
+          <literal>NOT MATCHED BY SOURCE</literal>, or
+          <literal>NOT MATCHED [BY TARGET]</literal>.
          </para>
         </listitem>
         <listitem>
@@ -615,7 +646,8 @@ MERGE <replaceable class="parameter">tot
   <para>
    If a <literal>WHEN</literal> clause omits an <literal>AND</literal>
    sub-clause, it becomes the final reachable clause of that
-   kind (<literal>MATCHED</literal> or <literal>NOT MATCHED</literal>).
+   kind (<literal>MATCHED</literal>, <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>).
    If a later <literal>WHEN</literal> clause of that kind
    is specified it would be provably unreachable and an error is raised.
    If no final reachable clause is specified of either kind, it is
@@ -701,6 +733,23 @@ RETURNING merge_action(), w.*;
    temporary table recently loaded into the database.
   </para>
 
+  <para>
+   Update <literal>wines</literal> based on a replacement wine list, inserting
+   rows for any new stock, updating modified stock entries, and deleting any
+   wines not present in the new list.
+<programlisting>
+MERGE INTO wines w
+USING new_wine_list s
+ON s.winename = w.winename
+WHEN NOT MATCHED BY TARGET THEN
+  INSERT VALUES(s.winename, s.stock)
+WHEN MATCHED AND w.stock != s.stock THEN
+  UPDATE SET stock = s.stock
+WHEN NOT MATCHED BY SOURCE THEN
+  DELETE;
+</programlisting>
+  </para>
+
  </refsect1>
 
  <refsect1>
@@ -709,7 +758,9 @@ RETURNING merge_action(), w.*;
     This command conforms to the <acronym>SQL</acronym> standard.
   </para>
    <para>
-    The <literal>WITH</literal> clause, <literal>DO NOTHING</literal> action,
+    The <literal>WITH</literal> clause, <literal>BY SOURCE</literal> and
+    <literal>BY TARGET</literal> qualifiers to
+    <literal>WHEN NOT MATCHED</literal>, <literal>DO NOTHING</literal> action,
     and <literal>RETURNING</literal> clause are extensions to the
     <acronym>SQL</acronym> standard.
   </para>
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
new file mode 100644
index 7eb1f7d..4d7c92d
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -1251,8 +1251,10 @@ InitResultRelInfo(ResultRelInfo *resultR
 	resultRelInfo->ri_ReturningSlot = NULL;
 	resultRelInfo->ri_TrigOldSlot = NULL;
 	resultRelInfo->ri_TrigNewSlot = NULL;
-	resultRelInfo->ri_matchedMergeAction = NIL;
-	resultRelInfo->ri_notMatchedMergeAction = NIL;
+	resultRelInfo->ri_MergeActions[MERGE_WHEN_MATCHED] = NIL;
+	resultRelInfo->ri_MergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = NIL;
+	resultRelInfo->ri_MergeActions[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = NIL;
+	resultRelInfo->ri_MergeJoinCondition = NULL;
 
 	/*
 	 * Only ExecInitPartitionInfo() and ExecInitPartitionDispatchInfo() pass
diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
new file mode 100644
index 64fcb01..f511092
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -880,6 +880,7 @@ ExecInitPartitionInfo(ModifyTableState *
 		List	   *firstMergeActionList = linitial(node->mergeActionLists);
 		ListCell   *lc;
 		ExprContext *econtext = mtstate->ps.ps_ExprContext;
+		Node	   *joinCondition;
 
 		if (part_attmap == NULL)
 			part_attmap =
@@ -890,23 +891,31 @@ ExecInitPartitionInfo(ModifyTableState *
 		if (unlikely(!leaf_part_rri->ri_projectNewInfoValid))
 			ExecInitMergeTupleSlots(mtstate, leaf_part_rri);
 
+		/* Initialize state for join condition-checking. */
+		joinCondition =
+			map_variable_attnos(linitial(node->mergeJoinConditions),
+								firstVarno, 0,
+								part_attmap,
+								RelationGetForm(partrel)->reltype,
+								&found_whole_row);
+		/* We ignore the value of found_whole_row. */
+		leaf_part_rri->ri_MergeJoinCondition =
+			ExecInitQual((List *) joinCondition, &mtstate->ps);
+
 		foreach(lc, firstMergeActionList)
 		{
 			/* Make a copy for this relation to be safe.  */
 			MergeAction *action = copyObject(lfirst(lc));
 			MergeActionState *action_state;
-			List	  **list;
 
 			/* Generate the action's state for this relation */
 			action_state = makeNode(MergeActionState);
 			action_state->mas_action = action;
 
 			/* And put the action in the appropriate list */
-			if (action->matched)
-				list = &leaf_part_rri->ri_matchedMergeAction;
-			else
-				list = &leaf_part_rri->ri_notMatchedMergeAction;
-			*list = lappend(*list, action_state);
+			leaf_part_rri->ri_MergeActions[action->matchKind] =
+				lappend(leaf_part_rri->ri_MergeActions[action->matchKind],
+						action_state);
 
 			switch (action->commandType)
 			{
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
new file mode 100644
index 4abfe82..ff76830
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -24,13 +24,15 @@
  *		values plus row-locating info for UPDATE and MERGE cases, or just the
  *		row-locating info for DELETE cases.
  *
- *		MERGE runs a join between the source relation and the target
- *		table; if any WHEN NOT MATCHED clauses are present, then the
- *		join is an outer join.  In this case, any unmatched tuples will
- *		have NULL row-locating info, and only INSERT can be run. But for
- *		matched tuples, then row-locating info is used to determine the
- *		tuple to UPDATE or DELETE. When all clauses are WHEN MATCHED,
- *		then an inner join is used, so all tuples contain row-locating info.
+ *		MERGE runs a join between the source relation and the target table.
+ *		If any WHEN NOT MATCHED [BY TARGET] clauses are present, then the join
+ *		is an outer join that might output tuples without a matching target
+ *		tuple.  In this case, any unmatched target tuples will have NULL
+ *		row-locating info, and only INSERT can be run.  But for matched
+ *		target tuples, the row-locating info is used to determine the tuple
+ *		to UPDATE or DELETE.  When all clauses are WHEN MATCHED or WHEN NOT
+ *		MATCHED BY SOURCE, all tuples produced by the join will include a
+ *		matching target tuple, so all tuples contain row-locating info.
  *
  *		If the query specifies RETURNING, then the ModifyTable returns a
  *		RETURNING tuple after completing each row insert, update, or delete.
@@ -2714,48 +2716,61 @@ ExecMerge(ModifyTableContext *context, R
 	bool		matched;
 
 	/*-----
-	 * If we are dealing with a WHEN MATCHED case (tupleid or oldtuple is
-	 * valid, depending on whether the result relation is a table or a view),
-	 * we execute the first action for which the additional WHEN MATCHED AND
+	 * If we are dealing with a WHEN MATCHED case, tupleid or oldtuple is
+	 * valid, depending on whether the result relation is a table or a view.
+	 * We execute the first action for which the additional WHEN MATCHED AND
 	 * quals pass.  If an action without quals is found, that action is
 	 * executed.
 	 *
-	 * Similarly, if we are dealing with WHEN NOT MATCHED case, we look at
-	 * the given WHEN NOT MATCHED actions in sequence until one passes.
+	 * Similarly, in the WHEN NOT MATCHED BY SOURCE case, tupleid or oldtuple
+	 * is valid, and we look at the given WHEN NOT MATCHED BY SOURCE actions
+	 * in sequence until one passes.  This is almost identical to the WHEN
+	 * MATCHED case, and both cases are handled by ExecMergeMatched().
+	 *
+	 * Finally, in the WHEN NOT MATCHED [BY TARGET] case, both tupleid and
+	 * oldtuple are invalid, and we look at the given WHEN NOT MATCHED [BY
+	 * TARGET] actions in sequence until one passes.
 	 *
 	 * Things get interesting in case of concurrent update/delete of the
 	 * target tuple. Such concurrent update/delete is detected while we are
-	 * executing a WHEN MATCHED action.
+	 * executing a WHEN MATCHED or WHEN NOT MATCHED BY SOURCE action.
 	 *
 	 * A concurrent update can:
 	 *
 	 * 1. modify the target tuple so that it no longer satisfies the
-	 *    additional quals attached to the current WHEN MATCHED action
+	 *    additional quals attached to the current WHEN MATCHED or WHEN NOT
+	 *    MATCHED BY SOURCE action, but still satisfies the join quals.
 	 *
-	 *    In this case, we are still dealing with a WHEN MATCHED case.
-	 *    We recheck the list of WHEN MATCHED actions from the start and
-	 *    choose the first one that satisfies the new target tuple.
+	 *    In this case, we are still dealing with the same kind of match
+	 *    (MATCHED or NOT MATCHED BY SOURCE).  We recheck the same list of
+	 *    actions from the start and choose the first one that satisfies the
+	 *    new target tuple.
 	 *
 	 * 2. modify the target tuple so that the join quals no longer pass and
-	 *    hence the source tuple no longer has a match.
+	 *    hence the source and target tuples no longer match.
 	 *
-	 *    In this case, the source tuple no longer matches the target tuple,
-	 *    so we now instead find a qualifying WHEN NOT MATCHED action to
-	 *    execute.
+	 *    In this case, we are now dealing with a NOT MATCHED case, and we
+	 *    process both WHEN NOT MATCHED BY SOURCE and WHEN NOT MATCHED [BY
+	 *    TARGET] actions.  First ExecMergeMatched() processes the list of
+	 *    WHEN NOT MATCHED BY SOURCE actions in sequence until one passes,
+	 *    then ExecMergeNotMatched() processes any WHEN NOT MATCHED [BY
+	 *    TARGET] actions in sequence until one passes.  Thus we may execute
+	 *    two actions; one of each kind.
 	 *
 	 * XXX Hmmm, what if the updated tuple would now match one that was
 	 * considered NOT MATCHED so far?
 	 *
-	 * A concurrent delete changes a WHEN MATCHED case to WHEN NOT MATCHED.
+	 * A concurrent delete changes a WHEN MATCHED case to WHEN NOT MATCHED
+	 * [BY TARGET].
 	 *
 	 * ExecMergeMatched takes care of following the update chain and
-	 * re-finding the qualifying WHEN MATCHED action, as long as the updated
-	 * target tuple still satisfies the join quals, i.e., it remains a WHEN
-	 * MATCHED case. If the tuple gets deleted or the join quals fail, it
-	 * returns and we try ExecMergeNotMatched. Given that ExecMergeMatched
-	 * always make progress by following the update chain and we never switch
-	 * from ExecMergeNotMatched to ExecMergeMatched, there is no risk of a
-	 * livelock.
+	 * re-finding the qualifying WHEN MATCHED or WHEN NOT MATCHED BY SOURCE
+	 * action, as long as the target tuple still exists. If the target tuple
+	 * gets deleted or a concurrent update causes the join quals to fail, it
+	 * returns a matched status of false and we call ExecMergeNotMatched.
+	 * Given that ExecMergeMatched always makes progress by following the
+	 * update chain and we never switch from ExecMergeNotMatched to
+	 * ExecMergeMatched, there is no risk of a livelock.
 	 */
 	matched = tupleid != NULL || oldtuple != NULL;
 	if (matched)
@@ -2768,33 +2783,52 @@ ExecMerge(ModifyTableContext *context, R
 	 * "matched" to false, indicating that it no longer matches).
 	 */
 	if (!matched)
-		rslot = ExecMergeNotMatched(context, resultRelInfo, canSetTag);
+	{
+		/*
+		 * If a concurrent update turned a MATCHED case into a NOT MATCHED
+		 * case, and we have both WHEN NOT MATCHED BY SOURCE and WHEN NOT
+		 * MATCHED [BY TARGET] actions, and there is a RETURNING clause,
+		 * ExecMergeMatched() may have already executed a WHEN NOT MATCHED BY
+		 * SOURCE action, and computed the row to return.  If so, we cannot
+		 * execute the WHEN NOT MATCHED [BY TARGET] action now, so mark it as
+		 * pending (to be processed on the next call to ExecModifyTable()).
+		 * Otherwise, just process the action now.
+		 */
+		if (rslot == NULL)
+			rslot = ExecMergeNotMatched(context, resultRelInfo, canSetTag);
+		else
+			context->mtstate->mt_merge_pending_not_matched = context->planSlot;
+	}
 
 	return rslot;
 }
 
 /*
- * Check and execute the first qualifying MATCHED action.  If the target
+ * Check and execute the first qualifying MATCHED or NOT MATCHED BY SOURCE
+ * action, depending on whether the join quals are satisfied.  If the target
  * relation is a table, the current target tuple is identified by tupleid.
  * Otherwise, if the target relation is a view, oldtuple is the current target
  * tuple from the view.
  *
- * We start from the first WHEN MATCHED action and check if the WHEN quals
- * pass, if any. If the WHEN quals for the first action do not pass, we
- * check the second, then the third and so on. If we reach to the end, no
- * action is taken and "matched" is set to true, indicating that no further
- * action is required for this tuple.
+ * We start from the first WHEN MATCHED or WHEN NOT MATCHED BY SOURCE action
+ * and check if the WHEN quals pass, if any. If the WHEN quals for the first
+ * action do not pass, we check the second, then the third and so on. If we
+ * reach the end without finding a qualifying action, we return NULL.
+ * Otherwise, we execute the qualifying action and return its RETURNING
+ * result, if any, or NULL.
  *
- * If we do find a qualifying action, then we attempt to execute the action.
+ * On entry, "*matched" is assumed to be true.  If a concurrent update or
+ * delete is detected that causes the join quals to no longer pass, we set it
+ * to false, indicating that the caller should process any NOT MATCHED [BY
+ * TARGET] actions.
  *
- * If the tuple is concurrently updated, EvalPlanQual is run with the updated
- * tuple to recheck the join quals. Note that the additional quals associated
- * with individual actions are evaluated by this routine via ExecQual, while
- * EvalPlanQual checks for the join quals. If EvalPlanQual tells us that the
- * updated tuple still passes the join quals, then we restart from the first
- * action to look for a qualifying action. Otherwise, "matched" is set to
- * false -- meaning that a NOT MATCHED action must now be executed for the
- * current source tuple.
+ * After a concurrent update, we restart from the first action to look for a
+ * new qualifying action to execute. If the join quals originally passed, and
+ * the concurrent update caused them to no longer pass, then we switch from
+ * the MATCHED to the NOT MATCHED BY SOURCE list of actions before restarting
+ * (and setting "*matched" to false).  As a result we may execute a WHEN NOT
+ * MATCHED BY SOURCE action, and set "*matched" to false, causing the caller
+ * to also execute a WHEN NOT MATCHED [BY TARGET] action.
  */
 static TupleTableSlot *
 ExecMergeMatched(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
@@ -2802,6 +2836,8 @@ ExecMergeMatched(ModifyTableContext *con
 				 bool *matched)
 {
 	ModifyTableState *mtstate = context->mtstate;
+	List	  **mergeActions = resultRelInfo->ri_MergeActions;
+	List	   *actionStates;
 	TupleTableSlot *newslot = NULL;
 	TupleTableSlot *rslot = NULL;
 	EState	   *estate = context->estate;
@@ -2810,54 +2846,58 @@ ExecMergeMatched(ModifyTableContext *con
 	EPQState   *epqstate = &mtstate->mt_epqstate;
 	ListCell   *l;
 
+	/* Expect matched to be true on entry */
+	Assert(*matched == true);
+
 	/*
-	 * If there are no WHEN MATCHED actions, we are done.
+	 * If there are no WHEN MATCHED or WHEN NOT MATCHED BY SOURCE actions, we
+	 * are done.
 	 */
-	if (resultRelInfo->ri_matchedMergeAction == NIL)
-	{
-		*matched = true;
+	if (mergeActions[MERGE_WHEN_MATCHED] == NIL &&
+		mergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] == NIL)
 		return NULL;
-	}
 
 	/*
 	 * Make tuple and any needed join variables available to ExecQual and
 	 * ExecProject. The target's existing tuple is installed in the scantuple.
-	 * Again, this target relation's slot is required only in the case of a
-	 * MATCHED tuple and UPDATE/DELETE actions.
+	 * This target relation's slot is required only in the case of a MATCHED
+	 * or NOT MATCHED BY SOURCE tuple and UPDATE/DELETE actions.
 	 */
 	econtext->ecxt_scantuple = resultRelInfo->ri_oldTupleSlot;
 	econtext->ecxt_innertuple = context->planSlot;
 	econtext->ecxt_outertuple = NULL;
 
 	/*
-	 * This routine is only invoked for matched rows, so we should either have
-	 * the tupleid of the target row, or an old tuple from the target wholerow
-	 * junk attr.
+	 * This routine is only invoked for matched target rows, so we should
+	 * either have the tupleid of the target row, or an old tuple from the
+	 * target wholerow junk attr.
 	 */
 	Assert(tupleid != NULL || oldtuple != NULL);
 	if (oldtuple != NULL)
 		ExecForceStoreHeapTuple(oldtuple, resultRelInfo->ri_oldTupleSlot,
 								false);
-
-lmerge_matched:
+	else if (!table_tuple_fetch_row_version(resultRelInfo->ri_RelationDesc,
+											tupleid,
+											SnapshotAny,
+											resultRelInfo->ri_oldTupleSlot))
+		elog(ERROR, "failed to fetch the target tuple");
 
 	/*
-	 * If passed a tupleid, use it to fetch the old target row.
+	 * Test the join condition.  If it's satisfied, perform a MATCHED action;
+	 * otherwise, perform a NOT MATCHED BY SOURCE action.
 	 *
-	 * We use SnapshotAny for this because we might get called again after
-	 * EvalPlanQual returns us a new tuple, which may not be visible to our
-	 * MVCC snapshot.
+	 * Note that this join condition will be NULL if there are no NOT MATCHED
+	 * BY SOURCE actions --- see transform_MERGE_to_join().  In that case, we
+	 * need only consider MATCHED actions here.
 	 */
-	if (tupleid != NULL)
-	{
-		if (!table_tuple_fetch_row_version(resultRelInfo->ri_RelationDesc,
-										   tupleid,
-										   SnapshotAny,
-										   resultRelInfo->ri_oldTupleSlot))
-			elog(ERROR, "failed to fetch the target tuple");
-	}
+	if (ExecQual(resultRelInfo->ri_MergeJoinCondition, econtext))
+		actionStates = mergeActions[MERGE_WHEN_MATCHED];
+	else
+		actionStates = mergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE];
 
-	foreach(l, resultRelInfo->ri_matchedMergeAction)
+lmerge_matched:
+
+	foreach(l, actionStates)
 	{
 		MergeActionState *relaction = (MergeActionState *) lfirst(l);
 		CmdType		commandType = relaction->mas_action->commandType;
@@ -2912,10 +2952,8 @@ lmerge_matched:
 										tupleid, NULL, newslot, &result))
 				{
 					if (result == TM_Ok)
-					{
-						*matched = true;
 						return NULL;	/* "do nothing" */
-					}
+
 					break;		/* concurrent update/delete */
 				}
 
@@ -2925,10 +2963,7 @@ lmerge_matched:
 				{
 					if (!ExecIRUpdateTriggers(estate, resultRelInfo,
 											  oldtuple, newslot))
-					{
-						*matched = true;
 						return NULL;	/* "do nothing" */
-					}
 				}
 				else
 				{
@@ -2948,7 +2983,6 @@ lmerge_matched:
 					if (updateCxt.crossPartUpdate)
 					{
 						mtstate->mt_merge_updated += 1;
-						*matched = true;
 						return context->cpUpdateReturningSlot;
 					}
 				}
@@ -2967,10 +3001,8 @@ lmerge_matched:
 										NULL, NULL, &result))
 				{
 					if (result == TM_Ok)
-					{
-						*matched = true;
 						return NULL;	/* "do nothing" */
-					}
+
 					break;		/* concurrent update/delete */
 				}
 
@@ -2980,10 +3012,7 @@ lmerge_matched:
 				{
 					if (!ExecIRDeleteTriggers(estate, resultRelInfo,
 											  oldtuple))
-					{
-						*matched = true;
 						return NULL;	/* "do nothing" */
-					}
 				}
 				else
 					result = ExecDeleteAct(context, resultRelInfo, tupleid,
@@ -3003,7 +3032,7 @@ lmerge_matched:
 				break;
 
 			default:
-				elog(ERROR, "unknown action in MERGE WHEN MATCHED clause");
+				elog(ERROR, "unknown action in MERGE WHEN clause");
 		}
 
 		switch (result)
@@ -3060,14 +3089,15 @@ lmerge_matched:
 							 errmsg("could not serialize access due to concurrent delete")));
 
 				/*
-				 * If the tuple was already deleted, return to let caller
-				 * handle it under NOT MATCHED clauses.
+				 * If the tuple was already deleted, set matched to false to
+				 * let caller handle it under NOT MATCHED [BY TARGET] clauses.
 				 */
 				*matched = false;
 				return NULL;
 
 			case TM_Updated:
 				{
+					bool		was_matched;
 					Relation	resultRelationDesc;
 					TupleTableSlot *epqslot,
 							   *inputslot;
@@ -3075,19 +3105,23 @@ lmerge_matched:
 
 					/*
 					 * The target tuple was concurrently updated by some other
-					 * transaction. Run EvalPlanQual() with the new version of
-					 * the tuple. If it does not return a tuple, then we
-					 * switch to the NOT MATCHED list of actions. If it does
-					 * return a tuple and the join qual is still satisfied,
-					 * then we just need to recheck the MATCHED actions,
-					 * starting from the top, and execute the first qualifying
-					 * action.
+					 * transaction.  If we are currently processing a MATCHED
+					 * action, use EvalPlanQual() with the new version of the
+					 * tuple and recheck the join qual, to detect a change
+					 * from the MATCHED to the NOT MATCHED cases.  If we are
+					 * already processing a NOT MATCHED BY SOURCE action, we
+					 * skip this (cannot switch from NOT MATCHED BY SOURCE to
+					 * MATCHED).
 					 */
+					was_matched = relaction->mas_action->matchKind == MERGE_WHEN_MATCHED;
 					resultRelationDesc = resultRelInfo->ri_RelationDesc;
 					lockmode = ExecUpdateLockMode(estate, resultRelInfo);
 
-					inputslot = EvalPlanQualSlot(epqstate, resultRelationDesc,
-												 resultRelInfo->ri_RangeTableIndex);
+					if (was_matched)
+						inputslot = EvalPlanQualSlot(epqstate, resultRelationDesc,
+													 resultRelInfo->ri_RangeTableIndex);
+					else
+						inputslot = resultRelInfo->ri_oldTupleSlot;
 
 					result = table_tuple_lock(resultRelationDesc, tupleid,
 											  estate->es_snapshot,
@@ -3098,34 +3132,9 @@ lmerge_matched:
 					switch (result)
 					{
 						case TM_Ok:
-							epqslot = EvalPlanQual(epqstate,
-												   resultRelationDesc,
-												   resultRelInfo->ri_RangeTableIndex,
-												   inputslot);
 
 							/*
-							 * If we got no tuple, or the tuple we get has a
-							 * NULL ctid, go back to caller: this one is not a
-							 * MATCHED tuple anymore, so they can retry with
-							 * NOT MATCHED actions.
-							 */
-							if (TupIsNull(epqslot))
-							{
-								*matched = false;
-								return NULL;
-							}
-
-							(void) ExecGetJunkAttribute(epqslot,
-														resultRelInfo->ri_RowIdAttNo,
-														&isNull);
-							if (isNull)
-							{
-								*matched = false;
-								return NULL;
-							}
-
-							/*
-							 * When a tuple was updated and migrated to
+							 * If the tuple was updated and migrated to
 							 * another partition concurrently, the current
 							 * MERGE implementation can't follow.  There's
 							 * probably a better way to handle this case, but
@@ -3136,26 +3145,72 @@ lmerge_matched:
 							if (ItemPointerIndicatesMovedPartitions(&context->tmfd.ctid))
 								ereport(ERROR,
 										(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
-										 errmsg("tuple to be deleted was already moved to another partition due to concurrent update")));
+										 errmsg("tuple to be merged was already moved to another partition due to concurrent update")));
 
 							/*
-							 * A non-NULL ctid means that we are still dealing
-							 * with MATCHED case. Restart the loop so that we
-							 * apply all the MATCHED rules again, to ensure
-							 * that the first qualifying WHEN MATCHED action
-							 * is executed.
-							 *
-							 * Update tupleid to that of the new tuple, for
-							 * the refetch we do at the top.
+							 * If this was a MATCHED case, use EvalPlanQual()
+							 * to recheck the join condition.
+							 */
+							if (was_matched)
+							{
+								epqslot = EvalPlanQual(epqstate,
+													   resultRelationDesc,
+													   resultRelInfo->ri_RangeTableIndex,
+													   inputslot);
+
+								/*
+								 * If the subplan didn't return a tuple, then
+								 * we must be dealing with an inner join for
+								 * which the join condition no longer matches.
+								 * This can only happen if there are no NOT
+								 * MATCHED actions, and so there is nothing
+								 * more to do.
+								 */
+								if (TupIsNull(epqslot))
+									return NULL;
+
+								/*
+								 * If we got a NULL ctid from the subplan, the
+								 * join quals no longer pass and we switch to
+								 * the NOT MATCHED BY SOURCE case.
+								 */
+								(void) ExecGetJunkAttribute(epqslot,
+															resultRelInfo->ri_RowIdAttNo,
+															&isNull);
+								if (isNull)
+									*matched = false;
+
+								/*
+								 * Otherwise, recheck the join quals to see if
+								 * we need to switch to the NOT MATCHED BY
+								 * SOURCE case.
+								 */
+								if (!table_tuple_fetch_row_version(resultRelationDesc,
+																   &context->tmfd.ctid,
+																   SnapshotAny,
+																   resultRelInfo->ri_oldTupleSlot))
+									elog(ERROR, "failed to fetch the target tuple");
+
+								if (*matched)
+									*matched = ExecQual(resultRelInfo->ri_MergeJoinCondition,
+														econtext);
+
+								/* Switch lists, if necessary */
+								if (!*matched)
+									actionStates = mergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE];
+							}
+
+							/*
+							 * Loop back and process the MATCHED or NOT
+							 * MATCHED BY SOURCE actions from the start.
 							 */
-							ItemPointerCopy(&context->tmfd.ctid, tupleid);
 							goto lmerge_matched;
 
 						case TM_Deleted:
 
 							/*
 							 * tuple already deleted; tell caller to run NOT
-							 * MATCHED actions
+							 * MATCHED [BY TARGET] actions
 							 */
 							*matched = false;
 							return NULL;
@@ -3239,13 +3294,11 @@ lmerge_matched:
 	/*
 	 * Successfully executed an action or no qualifying action was found.
 	 */
-	*matched = true;
-
 	return rslot;
 }
 
 /*
- * Execute the first qualifying NOT MATCHED action.
+ * Execute the first qualifying NOT MATCHED [BY TARGET] action.
  */
 static TupleTableSlot *
 ExecMergeNotMatched(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
@@ -3253,7 +3306,7 @@ ExecMergeNotMatched(ModifyTableContext *
 {
 	ModifyTableState *mtstate = context->mtstate;
 	ExprContext *econtext = mtstate->ps.ps_ExprContext;
-	List	   *actionStates = NIL;
+	List	   *actionStates;
 	TupleTableSlot *rslot = NULL;
 	ListCell   *l;
 
@@ -3266,7 +3319,7 @@ ExecMergeNotMatched(ModifyTableContext *
 	 * XXX does this mean that we can avoid creating copies of actionStates on
 	 * partitioned tables, for not-matched actions?
 	 */
-	actionStates = resultRelInfo->ri_notMatchedMergeAction;
+	actionStates = resultRelInfo->ri_MergeActions[MERGE_WHEN_NOT_MATCHED_BY_TARGET];
 
 	/*
 	 * Make source tuple available to ExecQual and ExecProject. We don't need
@@ -3360,9 +3413,11 @@ ExecInitMerge(ModifyTableState *mtstate,
 	foreach(lc, node->mergeActionLists)
 	{
 		List	   *mergeActionList = lfirst(lc);
+		Node	   *joinCondition;
 		TupleDesc	relationDesc;
 		ListCell   *l;
 
+		joinCondition = (Node *) list_nth(node->mergeJoinConditions, i);
 		resultRelInfo = mtstate->resultRelInfo + i;
 		i++;
 		relationDesc = RelationGetDescr(resultRelInfo->ri_RelationDesc);
@@ -3371,13 +3426,16 @@ ExecInitMerge(ModifyTableState *mtstate,
 		if (unlikely(!resultRelInfo->ri_projectNewInfoValid))
 			ExecInitMergeTupleSlots(mtstate, resultRelInfo);
 
+		/* initialize state for join condition-checking */
+		resultRelInfo->ri_MergeJoinCondition =
+			ExecInitQual((List *) joinCondition, &mtstate->ps);
+
 		foreach(l, mergeActionList)
 		{
 			MergeAction *action = (MergeAction *) lfirst(l);
 			MergeActionState *action_state;
 			TupleTableSlot *tgtslot;
 			TupleDesc	tgtdesc;
-			List	  **list;
 
 			/*
 			 * Build action merge state for this rel.  (For partitions,
@@ -3389,15 +3447,12 @@ ExecInitMerge(ModifyTableState *mtstate,
 													  &mtstate->ps);
 
 			/*
-			 * We create two lists - one for WHEN MATCHED actions and one for
-			 * WHEN NOT MATCHED actions - and stick the MergeActionState into
-			 * the appropriate list.
+			 * We create three lists - one for each MergeMatchKind - and stick
+			 * the MergeActionState into the appropriate list.
 			 */
-			if (action_state->mas_action->matched)
-				list = &resultRelInfo->ri_matchedMergeAction;
-			else
-				list = &resultRelInfo->ri_notMatchedMergeAction;
-			*list = lappend(*list, action_state);
+			resultRelInfo->ri_MergeActions[action->matchKind] =
+				lappend(resultRelInfo->ri_MergeActions[action->matchKind],
+						action_state);
 
 			switch (action->commandType)
 			{
@@ -3754,6 +3809,31 @@ ExecModifyTable(PlanState *pstate)
 		if (pstate->ps_ExprContext)
 			ResetExprContext(pstate->ps_ExprContext);
 
+		/*
+		 * If there is a pending MERGE ... WHEN NOT MATCHED [BY TARGET] action
+		 * to execute, do so now --- see the comments in ExecMerge().
+		 */
+		if (node->mt_merge_pending_not_matched != NULL)
+		{
+			context.planSlot = node->mt_merge_pending_not_matched;
+
+			slot = ExecMergeNotMatched(&context, node->resultRelInfo,
+									   node->canSetTag);
+
+			/* Clear the pending action */
+			node->mt_merge_pending_not_matched = NULL;
+
+			/*
+			 * If we got a RETURNING result, return it to the caller.  We'll
+			 * continue the work on next call.
+			 */
+			if (slot)
+				return slot;
+
+			continue;			/* continue with the next tuple */
+		}
+
+		/* Fetch the next row from subplan */
 		context.planSlot = ExecProcNode(subplanstate);
 
 		/* No more tuples to process? */
@@ -4139,6 +4219,7 @@ ExecInitModifyTable(ModifyTable *node, E
 	mtstate->resultRelInfo = (ResultRelInfo *)
 		palloc(nrels * sizeof(ResultRelInfo));
 
+	mtstate->mt_merge_pending_not_matched = NULL;
 	mtstate->mt_merge_inserted = 0;
 	mtstate->mt_merge_updated = 0;
 	mtstate->mt_merge_deleted = 0;
diff --git a/src/backend/nodes/nodeFuncs.c b/src/backend/nodes/nodeFuncs.c
new file mode 100644
index 5b70280..4e0cd63
--- a/src/backend/nodes/nodeFuncs.c
+++ b/src/backend/nodes/nodeFuncs.c
@@ -2596,6 +2596,8 @@ query_tree_walker_impl(Query *query,
 		return true;
 	if (WALK(query->mergeActionList))
 		return true;
+	if (WALK(query->mergeJoinCondition))
+		return true;
 	if (WALK(query->returningList))
 		return true;
 	if (WALK(query->jointree))
@@ -3621,6 +3623,7 @@ query_tree_mutator_impl(Query *query,
 	MUTATE(query->withCheckOptions, query->withCheckOptions, List *);
 	MUTATE(query->onConflict, query->onConflict, OnConflictExpr *);
 	MUTATE(query->mergeActionList, query->mergeActionList, List *);
+	MUTATE(query->mergeJoinCondition, query->mergeJoinCondition, Node *);
 	MUTATE(query->returningList, query->returningList, List *);
 	MUTATE(query->jointree, query->jointree, FromExpr *);
 	MUTATE(query->setOperations, query->setOperations, Node *);
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
new file mode 100644
index 610f4a5..1d36665
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -311,7 +311,8 @@ static ModifyTable *make_modifytable(Pla
 									 List *updateColnosLists,
 									 List *withCheckOptionLists, List *returningLists,
 									 List *rowMarks, OnConflictExpr *onconflict,
-									 List *mergeActionLists, int epqParam);
+									 List *mergeActionLists, List *mergeJoinConditions,
+									 int epqParam);
 static GatherMerge *create_gather_merge_plan(PlannerInfo *root,
 											 GatherMergePath *best_path);
 
@@ -2835,6 +2836,7 @@ create_modifytable_plan(PlannerInfo *roo
 							best_path->rowMarks,
 							best_path->onconflict,
 							best_path->mergeActionLists,
+							best_path->mergeJoinConditions,
 							best_path->epqParam);
 
 	copy_generic_path_info(&plan->plan, &best_path->path);
@@ -7014,7 +7016,8 @@ make_modifytable(PlannerInfo *root, Plan
 				 List *updateColnosLists,
 				 List *withCheckOptionLists, List *returningLists,
 				 List *rowMarks, OnConflictExpr *onconflict,
-				 List *mergeActionLists, int epqParam)
+				 List *mergeActionLists, List *mergeJoinConditions,
+				 int epqParam)
 {
 	ModifyTable *node = makeNode(ModifyTable);
 	List	   *fdw_private_list;
@@ -7084,6 +7087,7 @@ make_modifytable(PlannerInfo *root, Plan
 	node->returningLists = returningLists;
 	node->rowMarks = rowMarks;
 	node->mergeActionLists = mergeActionLists;
+	node->mergeJoinConditions = mergeJoinConditions;
 	node->epqParam = epqParam;
 
 	/*
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
new file mode 100644
index 5564826..6318b18
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -905,6 +905,9 @@ subquery_planner(PlannerGlobal *glob, Qu
 								  EXPRKIND_QUAL);
 	}
 
+	parse->mergeJoinCondition =
+		preprocess_expression(root, parse->mergeJoinCondition, EXPRKIND_QUAL);
+
 	root->append_rel_list = (List *)
 		preprocess_expression(root, (Node *) root->append_rel_list,
 							  EXPRKIND_APPINFO);
@@ -1787,6 +1790,7 @@ grouping_planner(PlannerInfo *root, doub
 			List	   *withCheckOptionLists = NIL;
 			List	   *returningLists = NIL;
 			List	   *mergeActionLists = NIL;
+			List	   *mergeJoinConditions = NIL;
 			List	   *rowMarks;
 
 			if (bms_membership(root->all_result_relids) == BMS_MULTIPLE)
@@ -1893,6 +1897,19 @@ grouping_planner(PlannerInfo *root, doub
 						mergeActionLists = lappend(mergeActionLists,
 												   mergeActionList);
 					}
+					if (parse->commandType == CMD_MERGE)
+					{
+						Node	   *mergeJoinCondition = parse->mergeJoinCondition;
+
+						if (this_result_rel != top_result_rel)
+							mergeJoinCondition =
+								adjust_appendrel_attrs_multilevel(root,
+																  mergeJoinCondition,
+																  this_result_rel,
+																  top_result_rel);
+						mergeJoinConditions = lappend(mergeJoinConditions,
+													  mergeJoinCondition);
+					}
 				}
 
 				if (resultRelations == NIL)
@@ -1917,6 +1934,8 @@ grouping_planner(PlannerInfo *root, doub
 						returningLists = list_make1(parse->returningList);
 					if (parse->mergeActionList)
 						mergeActionLists = list_make1(parse->mergeActionList);
+					if (parse->commandType == CMD_MERGE)
+						mergeJoinConditions = list_make1(parse->mergeJoinCondition);
 				}
 			}
 			else
@@ -1932,6 +1951,8 @@ grouping_planner(PlannerInfo *root, doub
 					returningLists = list_make1(parse->returningList);
 				if (parse->mergeActionList)
 					mergeActionLists = list_make1(parse->mergeActionList);
+				if (parse->commandType == CMD_MERGE)
+					mergeJoinConditions = list_make1(parse->mergeJoinCondition);
 			}
 
 			/*
@@ -1959,6 +1980,7 @@ grouping_planner(PlannerInfo *root, doub
 										rowMarks,
 										parse->onConflict,
 										mergeActionLists,
+										mergeJoinConditions,
 										assign_special_exec_param(root));
 		}
 
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
new file mode 100644
index 42603db..37abcb4
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -1143,7 +1143,9 @@ set_plan_refs(PlannerInfo *root, Plan *p
 				 */
 				if (splan->mergeActionLists != NIL)
 				{
+					List	   *newMJC = NIL;
 					ListCell   *lca,
+							   *lcj,
 							   *lcr;
 
 					/*
@@ -1164,10 +1166,12 @@ set_plan_refs(PlannerInfo *root, Plan *p
 
 					itlist = build_tlist_index(subplan->targetlist);
 
-					forboth(lca, splan->mergeActionLists,
-							lcr, splan->resultRelations)
+					forthree(lca, splan->mergeActionLists,
+							 lcj, splan->mergeJoinConditions,
+							 lcr, splan->resultRelations)
 					{
 						List	   *mergeActionList = lfirst(lca);
+						Node	   *mergeJoinCondition = lfirst(lcj);
 						Index		resultrel = lfirst_int(lcr);
 
 						foreach(l, mergeActionList)
@@ -1192,7 +1196,19 @@ set_plan_refs(PlannerInfo *root, Plan *p
 																  NRM_EQUAL,
 																  NUM_EXEC_QUAL(plan));
 						}
+
+						/* Fix join condition too. */
+						mergeJoinCondition = (Node *)
+							fix_join_expr(root,
+										  (List *) mergeJoinCondition,
+										  NULL, itlist,
+										  resultrel,
+										  rtoffset,
+										  NRM_EQUAL,
+										  NUM_EXEC_QUAL(plan));
+						newMJC = lappend(newMJC, mergeJoinCondition);
 					}
+					splan->mergeJoinConditions = newMJC;
 				}
 
 				splan->nominalRelation += rtoffset;
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
new file mode 100644
index 300691c..2d8956d
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -153,9 +153,11 @@ transform_MERGE_to_join(Query *parse)
 {
 	RangeTblEntry *joinrte;
 	JoinExpr   *joinexpr;
+	bool		have_action[3];
 	JoinType	jointype;
 	int			joinrti;
 	List	   *vars;
+	RangeTblRef *rtr;
 
 	if (parse->commandType != CMD_MERGE)
 		return;
@@ -164,11 +166,27 @@ transform_MERGE_to_join(Query *parse)
 	vars = NIL;
 
 	/*
-	 * When any WHEN NOT MATCHED THEN INSERT clauses exist, we need to use an
-	 * outer join so that we process all unmatched tuples from the source
-	 * relation.  If none exist, we can use an inner join.
+	 * Work out what kind of join is required.  If there any WHEN NOT MATCHED
+	 * BY SOURCE/TARGET actions, an outer join is required so that we process
+	 * all unmatched tuples from the source and/or target relations.
+	 * Otherwise, we can use an inner join.
 	 */
-	if (parse->mergeUseOuterJoin)
+	have_action[MERGE_WHEN_MATCHED] = false;
+	have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	have_action[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
+
+	foreach_node(MergeAction, action, parse->mergeActionList)
+	{
+		if (action->commandType != CMD_NOTHING)
+			have_action[action->matchKind] = true;
+	}
+
+	if (have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] &&
+		have_action[MERGE_WHEN_NOT_MATCHED_BY_TARGET])
+		jointype = JOIN_FULL;
+	else if (have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE])
+		jointype = JOIN_LEFT;
+	else if (have_action[MERGE_WHEN_NOT_MATCHED_BY_TARGET])
 		jointype = JOIN_RIGHT;
 	else
 		jointype = JOIN_INNER;
@@ -204,16 +222,16 @@ transform_MERGE_to_join(Query *parse)
 	 * trigger-updatable view, it will be the expanded view subquery that we
 	 * need to pull data from.
 	 */
+	rtr = makeNode(RangeTblRef);
+	rtr->rtindex = parse->mergeTargetRelation;
 	joinexpr = makeNode(JoinExpr);
 	joinexpr->jointype = jointype;
 	joinexpr->isNatural = false;
-	joinexpr->larg = (Node *) makeNode(RangeTblRef);
-	((RangeTblRef *) joinexpr->larg)->rtindex = parse->mergeTargetRelation;
-	joinexpr->rarg = linitial(parse->jointree->fromlist);	/* original join */
+	joinexpr->larg = (Node *) makeFromExpr(list_make1(rtr), parse->jointree->quals);
+	joinexpr->rarg = linitial(parse->jointree->fromlist);	/* source rel */
 	joinexpr->usingClause = NIL;
 	joinexpr->join_using_alias = NULL;
-	/* The quals are removed from the jointree and into this specific join */
-	joinexpr->quals = parse->jointree->quals;
+	joinexpr->quals = parse->mergeJoinCondition;
 	joinexpr->alias = NULL;
 	joinexpr->rtindex = joinrti;
 
@@ -233,6 +251,15 @@ transform_MERGE_to_join(Query *parse)
 			add_nulling_relids((Node *) parse->targetList,
 							   bms_make_singleton(parse->mergeTargetRelation),
 							   bms_make_singleton(joinrti));
+
+	/*
+	 * If there are any WHEN NOT MATCHED BY SOURCE actions, the executor will
+	 * use the join condition to distinguish between MATCHED and NOT MATCHED
+	 * BY SOURCE cases.  Otherwise, it's no longer needed, and we set it to
+	 * NULL, saving cycles during planning and execution.
+	 */
+	if (!have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE])
+		parse->mergeJoinCondition = NULL;
 }
 
 /*
@@ -2173,6 +2200,8 @@ perform_pullup_replace_vars(PlannerInfo
 				pullup_replace_vars((Node *) action->targetList, rvcontext);
 		}
 	}
+	parse->mergeJoinCondition = pullup_replace_vars(parse->mergeJoinCondition,
+													rvcontext);
 	replace_vars_in_jointree((Node *) parse->jointree, rvcontext);
 	Assert(parse->setOperations == NULL);
 	parse->havingQual = pullup_replace_vars(parse->havingQual, rvcontext);
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
new file mode 100644
index 7698bfa..931b9c0
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -134,6 +134,7 @@ preprocess_targetlist(PlannerInfo *root)
 	if (command_type == CMD_MERGE)
 	{
 		ListCell   *l;
+		List	   *vars;
 
 		/*
 		 * For MERGE, handle targetlist of each MergeAction separately. Give
@@ -144,7 +145,6 @@ preprocess_targetlist(PlannerInfo *root)
 		foreach(l, parse->mergeActionList)
 		{
 			MergeAction *action = (MergeAction *) lfirst(l);
-			List	   *vars;
 			ListCell   *l2;
 
 			if (action->commandType == CMD_INSERT)
@@ -182,6 +182,30 @@ preprocess_targetlist(PlannerInfo *root)
 			}
 			list_free(vars);
 		}
+
+		/*
+		 * Add resjunk entries for any Vars and PlaceHolderVars used in the
+		 * join condition that belong to relations other than the target.  We
+		 * don't expect to see any aggregates or window functions here.
+		 */
+		vars = pull_var_clause(parse->mergeJoinCondition,
+							   PVC_INCLUDE_PLACEHOLDERS);
+		foreach(l, vars)
+		{
+			Var		   *var = (Var *) lfirst(l);
+			TargetEntry *tle;
+
+			if (IsA(var, Var) && var->varno == result_relation)
+				continue;		/* don't need it */
+
+			if (tlist_member((Expr *) var, tlist))
+				continue;		/* already got it */
+
+			tle = makeTargetEntry((Expr *) var,
+								  list_length(tlist) + 1,
+								  NULL, true);
+			tlist = lappend(tlist, tle);
+		}
 	}
 
 	/*
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
new file mode 100644
index 246cd8f..e73b883
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -3702,6 +3702,7 @@ create_lockrows_path(PlannerInfo *root,
  * 'onconflict' is the ON CONFLICT clause, or NULL
  * 'epqParam' is the ID of Param for EvalPlanQual re-eval
  * 'mergeActionLists' is a list of lists of MERGE actions (one per rel)
+ * 'mergeJoinConditions' is a list of join conditions for MERGE (one per rel)
  */
 ModifyTablePath *
 create_modifytable_path(PlannerInfo *root, RelOptInfo *rel,
@@ -3713,7 +3714,8 @@ create_modifytable_path(PlannerInfo *roo
 						List *updateColnosLists,
 						List *withCheckOptionLists, List *returningLists,
 						List *rowMarks, OnConflictExpr *onconflict,
-						List *mergeActionLists, int epqParam)
+						List *mergeActionLists, List *mergeJoinConditions,
+						int epqParam)
 {
 	ModifyTablePath *pathnode = makeNode(ModifyTablePath);
 
@@ -3781,6 +3783,7 @@ create_modifytable_path(PlannerInfo *roo
 	pathnode->onconflict = onconflict;
 	pathnode->epqParam = epqParam;
 	pathnode->mergeActionLists = mergeActionLists;
+	pathnode->mergeJoinConditions = mergeJoinConditions;
 
 	return pathnode;
 }
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index 39a801a..dd268bc
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -275,6 +275,7 @@ static Node *makeRecursiveViewSelect(cha
 	struct SelectLimit *selectlimit;
 	SetQuantifier setquantifier;
 	struct GroupClause *groupclause;
+	MergeMatchKind mergematch;
 	MergeWhenClause *mergewhen;
 	struct KeyActions *keyactions;
 	struct KeyAction *keyaction;
@@ -516,6 +517,7 @@ static Node *makeRecursiveViewSelect(cha
 %type <onconflict> opt_on_conflict
 %type <mergewhen>	merge_insert merge_update merge_delete
 
+%type <mergematch> merge_when_tgt_matched merge_when_tgt_not_matched
 %type <node>	merge_when_clause opt_merge_when_condition
 %type <list>	merge_when_list
 
@@ -760,11 +762,11 @@ static Node *makeRecursiveViewSelect(cha
 	SAVEPOINT SCALAR SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT
 	SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
-	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
+	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SOURCE SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRIP_P
 	SUBSCRIPTION SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
 
-	TABLE TABLES TABLESAMPLE TABLESPACE TEMP TEMPLATE TEMPORARY TEXT_P THEN
+	TABLE TABLES TABLESAMPLE TABLESPACE TARGET TEMP TEMPLATE TEMPORARY TEXT_P THEN
 	TIES TIME TIMESTAMP TO TRAILING TRANSACTION TRANSFORM
 	TREAT TRIGGER TRIM TRUE_P
 	TRUNCATE TRUSTED TYPE_P TYPES_P
@@ -12394,50 +12396,66 @@ merge_when_list:
 			| merge_when_list merge_when_clause		{ $$ = lappend($1,$2); }
 		;
 
+/*
+ * A WHEN clause may be WHEN MATCHED, WHEN NOT MATCHED BY SOURCE, or WHEN NOT
+ * MATCHED [BY TARGET]. The first two cases match target tuples, and support
+ * UPDATE/DELETE/DO NOTHING actions. The third case does not match target
+ * tuples, and only supports INSERT/DO NOTHING actions.
+ */
 merge_when_clause:
-			WHEN MATCHED opt_merge_when_condition THEN merge_update
+			merge_when_tgt_matched opt_merge_when_condition THEN merge_update
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN merge_delete
+			| merge_when_tgt_matched opt_merge_when_condition THEN merge_delete
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN merge_insert
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN merge_insert
 				{
-					$6->matched = false;
-					$6->condition = $4;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $6;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = true;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $3;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = false;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $4;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
 		;
 
+merge_when_tgt_matched:
+			WHEN MATCHED					{ $$ = MERGE_WHEN_MATCHED; }
+			| WHEN NOT MATCHED BY SOURCE	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_SOURCE; }
+		;
+
+merge_when_tgt_not_matched:
+			WHEN NOT MATCHED				{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+			| WHEN NOT MATCHED BY TARGET	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+		;
+
 opt_merge_when_condition:
 			AND a_expr				{ $$ = $2; }
 			|						{ $$ = NULL; }
@@ -17404,6 +17422,7 @@ unreserved_keyword:
 			| SIMPLE
 			| SKIP
 			| SNAPSHOT
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -17422,6 +17441,7 @@ unreserved_keyword:
 			| SYSTEM_P
 			| TABLES
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
@@ -18019,6 +18039,7 @@ bare_label_keyword:
 			| SMALLINT
 			| SNAPSHOT
 			| SOME
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -18042,6 +18063,7 @@ bare_label_keyword:
 			| TABLES
 			| TABLESAMPLE
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
diff --git a/src/backend/parser/parse_merge.c b/src/backend/parser/parse_merge.c
new file mode 100644
index 04ed5e6..bce11d5
--- a/src/backend/parser/parse_merge.c
+++ b/src/backend/parser/parse_merge.c
@@ -40,9 +40,9 @@ static void setNamespaceVisibilityForRTE
  * Make appropriate changes to the namespace visibility while transforming
  * individual action's quals and targetlist expressions. In particular, for
  * INSERT actions we must only see the source relation (since INSERT action is
- * invoked for NOT MATCHED tuples and hence there is no target tuple to deal
- * with). On the other hand, UPDATE and DELETE actions can see both source and
- * target relations.
+ * invoked for NOT MATCHED [BY TARGET] tuples and hence there is no target
+ * tuple to deal with). On the other hand, UPDATE and DELETE actions can see
+ * both source and target relations, unless invoked for NOT MATCHED BY SOURCE.
  *
  * Also, since the internal join node can hide the source and target
  * relations, we must explicitly make the respective relation as visible so
@@ -58,7 +58,7 @@ setNamespaceForMergeWhen(ParseState *pst
 	targetRelRTE = rt_fetch(targetRTI, pstate->p_rtable);
 	sourceRelRTE = rt_fetch(sourceRTI, pstate->p_rtable);
 
-	if (mergeWhenClause->matched)
+	if (mergeWhenClause->matchKind == MERGE_WHEN_MATCHED)
 	{
 		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
 			   mergeWhenClause->commandType == CMD_DELETE ||
@@ -70,11 +70,25 @@ setNamespaceForMergeWhen(ParseState *pst
 		setNamespaceVisibilityForRTE(pstate->p_namespace,
 									 sourceRelRTE, true, true);
 	}
-	else
+	else if (mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
 	{
 		/*
-		 * NOT MATCHED actions can't see target relation, but they can see
-		 * source relation.
+		 * NOT MATCHED BY SOURCE actions can see the target relation, but they
+		 * can't see the source relation.
+		 */
+		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
+			   mergeWhenClause->commandType == CMD_DELETE ||
+			   mergeWhenClause->commandType == CMD_NOTHING);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 targetRelRTE, true, true);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 sourceRelRTE, false, false);
+	}
+	else						/* MERGE_WHEN_NOT_MATCHED_BY_TARGET */
+	{
+		/*
+		 * NOT MATCHED [BY TARGET] actions can't see target relation, but they
+		 * can see source relation.
 		 */
 		Assert(mergeWhenClause->commandType == CMD_INSERT ||
 			   mergeWhenClause->commandType == CMD_NOTHING);
@@ -95,10 +109,9 @@ transformMergeStmt(ParseState *pstate, M
 	Query	   *qry = makeNode(Query);
 	ListCell   *l;
 	AclMode		targetPerms = ACL_NO_RIGHTS;
-	bool		is_terminal[2];
+	bool		is_terminal[3];
 	Index		sourceRTI;
 	List	   *mergeActionList;
-	Node	   *joinExpr;
 	ParseNamespaceItem *nsitem;
 
 	/* There can't be any outer WITH to worry about */
@@ -122,12 +135,12 @@ transformMergeStmt(ParseState *pstate, M
 	/*
 	 * Check WHEN clauses for permissions and sanity
 	 */
-	is_terminal[0] = false;
-	is_terminal[1] = false;
+	is_terminal[MERGE_WHEN_MATCHED] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
 	foreach(l, stmt->mergeWhenClauses)
 	{
 		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
-		int			when_type = (mergeWhenClause->matched ? 0 : 1);
 
 		/*
 		 * Collect permissions to check, according to action types. We require
@@ -157,12 +170,12 @@ transformMergeStmt(ParseState *pstate, M
 		/*
 		 * Check for unreachable WHEN clauses
 		 */
-		if (is_terminal[when_type])
+		if (is_terminal[mergeWhenClause->matchKind])
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
 					 errmsg("unreachable WHEN clause specified after unconditional WHEN clause")));
 		if (mergeWhenClause->condition == NULL)
-			is_terminal[when_type] = true;
+			is_terminal[mergeWhenClause->matchKind] = true;
 	}
 
 	/*
@@ -223,16 +236,15 @@ transformMergeStmt(ParseState *pstate, M
 	 * side, so add that to the namespace.
 	 */
 	addNSItemToQuery(pstate, pstate->p_target_nsitem, false, true, true);
-	joinExpr = transformExpr(pstate, stmt->joinCondition,
-							 EXPR_KIND_JOIN_ON);
+	qry->mergeJoinCondition = transformExpr(pstate, stmt->joinCondition,
+											EXPR_KIND_JOIN_ON);
 
 	/*
 	 * Create the temporary query's jointree using the joinlist we built using
-	 * just the source relation; the target relation is not included.  The
-	 * quals we use are the join conditions to the merge target.  The join
+	 * just the source relation; the target relation is not included. The join
 	 * will be constructed fully by transform_MERGE_to_join.
 	 */
-	qry->jointree = makeFromExpr(pstate->p_joinlist, joinExpr);
+	qry->jointree = makeFromExpr(pstate->p_joinlist, NULL);
 
 	/* Transform the RETURNING list, if any */
 	qry->returningList = transformReturningList(pstate, stmt->returningList,
@@ -260,11 +272,7 @@ transformMergeStmt(ParseState *pstate, M
 
 		action = makeNode(MergeAction);
 		action->commandType = mergeWhenClause->commandType;
-		action->matched = mergeWhenClause->matched;
-
-		/* Use an outer join if any INSERT actions exist in the command. */
-		if (action->commandType == CMD_INSERT)
-			qry->mergeUseOuterJoin = true;
+		action->matchKind = mergeWhenClause->matchKind;
 
 		/*
 		 * Set namespace for the specific action. This must be done before
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
new file mode 100644
index f2893d4..4d36375
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -7093,6 +7093,7 @@ get_merge_query_def(Query *query, depars
 	StringInfo	buf = context->buf;
 	RangeTblEntry *rte;
 	ListCell   *lc;
+	bool		haveNotMatchedBySource;
 
 	/* Insert the WITH clause if given */
 	get_with_clause(query, context);
@@ -7118,7 +7119,26 @@ get_merge_query_def(Query *query, depars
 	get_from_clause(query, " USING ", context);
 	appendContextKeyword(context, " ON ",
 						 -PRETTYINDENT_STD, PRETTYINDENT_STD, 2);
-	get_rule_expr(query->jointree->quals, context, false);
+	get_rule_expr(query->mergeJoinCondition, context, false);
+
+	/*
+	 * Test for any NOT MATCHED BY SOURCE actions.  If there are none, then
+	 * any NOT MATCHED BY TARGET actions are output as "WHEN NOT MATCHED", per
+	 * SQL standard.  Otherwise, we have a non-SQL-standard query, so output
+	 * "BY SOURCE" / "BY TARGET" qualifiers for all NOT MATCHED actions, to be
+	 * more explicit.
+	 */
+	haveNotMatchedBySource = false;
+	foreach(lc, query->mergeActionList)
+	{
+		MergeAction *action = lfirst_node(MergeAction, lc);
+
+		if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+		{
+			haveNotMatchedBySource = true;
+			break;
+		}
+	}
 
 	/* Print each merge action */
 	foreach(lc, query->mergeActionList)
@@ -7127,7 +7147,24 @@ get_merge_query_def(Query *query, depars
 
 		appendContextKeyword(context, " WHEN ",
 							 -PRETTYINDENT_STD, PRETTYINDENT_STD, 2);
-		appendStringInfo(buf, "%sMATCHED", action->matched ? "" : "NOT ");
+		switch (action->matchKind)
+		{
+			case MERGE_WHEN_MATCHED:
+				appendStringInfo(buf, "MATCHED");
+				break;
+			case MERGE_WHEN_NOT_MATCHED_BY_SOURCE:
+				appendStringInfo(buf, "NOT MATCHED BY SOURCE");
+				break;
+			case MERGE_WHEN_NOT_MATCHED_BY_TARGET:
+				if (haveNotMatchedBySource)
+					appendStringInfo(buf, "NOT MATCHED BY TARGET");
+				else
+					appendStringInfo(buf, "NOT MATCHED");
+				break;
+			default:
+				elog(ERROR, "unrecognized matchKind: %d",
+					 (int) action->matchKind);
+		}
 
 		if (action->qual)
 		{
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
new file mode 100644
index 56d723d..c6977a6
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -4335,17 +4335,35 @@ psql_completion(const char *text, int st
 			 TailMatches("USING", MatchAny, MatchAny, "ON", MatchAny, MatchAny, MatchAny, "WHEN"))
 		COMPLETE_WITH("MATCHED", "NOT MATCHED");
 
-	/* Complete ... WHEN [NOT] MATCHED with THEN/AND */
+	/*
+	 * Complete ... WHEN MATCHED and WHEN NOT MATCHED BY SOURCE|TARGET with
+	 * THEN/AND
+	 */
 	else if (TailMatches("WHEN", "MATCHED") ||
-			 TailMatches("WHEN", "NOT", "MATCHED"))
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE|TARGET"))
 		COMPLETE_WITH("THEN", "AND");
 
-	/* Complete ... WHEN MATCHED THEN with UPDATE SET/DELETE/DO NOTHING */
-	else if (TailMatches("WHEN", "MATCHED", "THEN"))
+	/* Complete ... WHEN NOT MATCHED with BY/THEN/AND */
+	else if (TailMatches("WHEN", "NOT", "MATCHED"))
+		COMPLETE_WITH("BY", "THEN", "AND");
+
+	/* Complete ... WHEN NOT MATCHED BY with SOURCE/TARGET */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "BY"))
+		COMPLETE_WITH("SOURCE", "TARGET");
+
+	/*
+	 * Complete ... WHEN MATCHED THEN and WHEN NOT MATCHED BY SOURCE THEN with
+	 * UPDATE SET/DELETE/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE", "THEN"))
 		COMPLETE_WITH("UPDATE SET", "DELETE", "DO NOTHING");
 
-	/* Complete ... WHEN NOT MATCHED THEN with INSERT/DO NOTHING */
-	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN"))
+	/*
+	 * Complete ... WHEN NOT MATCHED [BY TARGET] THEN with INSERT/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "TARGET", "THEN"))
 		COMPLETE_WITH("INSERT", "DO NOTHING");
 
 /* NOTIFY --- can be inside EXPLAIN, RULE, etc */
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
new file mode 100644
index 9259352..c2d047d
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -544,9 +544,11 @@ typedef struct ResultRelInfo
 	/* ON CONFLICT evaluation state */
 	OnConflictSetState *ri_onConflict;
 
-	/* for MERGE, lists of MergeActionState */
-	List	   *ri_matchedMergeAction;
-	List	   *ri_notMatchedMergeAction;
+	/* for MERGE, lists of MergeActionState (one per MergeMatchKind) */
+	List	   *ri_MergeActions[3];
+
+	/* for MERGE, join condition-checking expr state */
+	ExprState  *ri_MergeJoinCondition;
 
 	/* partition check expression state (NULL if not set up yet) */
 	ExprState  *ri_PartitionCheckExpr;
@@ -1328,6 +1330,13 @@ typedef struct ModifyTableState
 	/* For MERGE, the action currently being executed */
 	MergeActionState *mt_merge_action;
 
+	/*
+	 * For MERGE, if there is a pending NOT MATCHED [BY TARGET] action to be
+	 * performed, this will be the last tuple read from the subplan; otherwise
+	 * it will be NULL --- see the comments in ExecMerge().
+	 */
+	TupleTableSlot *mt_merge_pending_not_matched;
+
 	/* tuple counters for MERGE */
 	double		mt_merge_inserted;
 	double		mt_merge_updated;
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
new file mode 100644
index 7b57fdd..6b47eb7
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -176,8 +176,6 @@ typedef struct Query
 								 * also USING clause for MERGE */
 
 	List	   *mergeActionList;	/* list of actions for MERGE (only) */
-	/* whether to use outer join */
-	bool		mergeUseOuterJoin pg_node_attr(query_jumble_ignore);
 
 	/*
 	 * rtable index of target relation for MERGE to pull data. Initially, this
@@ -187,6 +185,9 @@ typedef struct Query
 	 */
 	int			mergeTargetRelation pg_node_attr(query_jumble_ignore);
 
+	/* join condition between source and target for MERGE */
+	Node	   *mergeJoinCondition;
+
 	List	   *targetList;		/* target list (of TargetEntry) */
 
 	/* OVERRIDING clause */
@@ -1677,7 +1678,7 @@ typedef struct CommonTableExpr
 typedef struct MergeWhenClause
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *condition;		/* WHEN conditions (raw parser) */
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
new file mode 100644
index 534692b..5ccfa5f
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -2367,6 +2367,8 @@ typedef struct ModifyTablePath
 	int			epqParam;		/* ID of Param for EvalPlanQual re-eval */
 	List	   *mergeActionLists;	/* per-target-table lists of actions for
 									 * MERGE */
+	List	   *mergeJoinConditions;	/* per-target-table join conditions
+										 * for MERGE */
 } ModifyTablePath;
 
 /*
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
new file mode 100644
index b4ef6bc..ebefd65
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -251,6 +251,8 @@ typedef struct ModifyTable
 	List	   *exclRelTlist;	/* tlist of the EXCLUDED pseudo relation */
 	List	   *mergeActionLists;	/* per-target-table lists of actions for
 									 * MERGE */
+	List	   *mergeJoinConditions;	/* per-target-table join conditions
+										 * for MERGE */
 } ModifyTable;
 
 struct PartitionPruneInfo;		/* forward reference to struct below */
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
new file mode 100644
index 8df8884..3b7b8de
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -1753,10 +1753,18 @@ typedef struct BooleanTest
  *
  * Transformed representation of a WHEN clause in a MERGE statement
  */
+
+typedef enum MergeMatchKind
+{
+	MERGE_WHEN_MATCHED,
+	MERGE_WHEN_NOT_MATCHED_BY_SOURCE,
+	MERGE_WHEN_NOT_MATCHED_BY_TARGET
+} MergeMatchKind;
+
 typedef struct MergeAction
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	/* OVERRIDING clause */
 	OverridingKind override pg_node_attr(query_jumble_ignore);
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
new file mode 100644
index c43d97b..1b3dd52
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -283,7 +283,8 @@ extern ModifyTablePath *create_modifytab
 												List *updateColnosLists,
 												List *withCheckOptionLists, List *returningLists,
 												List *rowMarks, OnConflictExpr *onconflict,
-												List *mergeActionLists, int epqParam);
+												List *mergeActionLists, List *mergeJoinConditions,
+												int epqParam);
 extern LimitPath *create_limit_path(PlannerInfo *root, RelOptInfo *rel,
 									Path *subpath,
 									Node *limitOffset, Node *limitCount,
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
new file mode 100644
index 0993534..45229ed
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -404,6 +404,7 @@ PG_KEYWORD("skip", SKIP, UNRESERVED_KEYW
 PG_KEYWORD("smallint", SMALLINT, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("snapshot", SNAPSHOT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("some", SOME, RESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("source", SOURCE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("sql", SQL_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("stable", STABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("standalone", STANDALONE_P, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -427,6 +428,7 @@ PG_KEYWORD("table", TABLE, RESERVED_KEYW
 PG_KEYWORD("tables", TABLES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablesample", TABLESAMPLE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablespace", TABLESPACE, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("target", TARGET, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temp", TEMP, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("template", TEMPLATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temporary", TEMPORARY, UNRESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/test/isolation/expected/merge-update.out b/src/test/isolation/expected/merge-update.out
new file mode 100644
index f5f7e3b..3063c0c
--- a/src/test/isolation/expected/merge-update.out
+++ b/src/test/isolation/expected/merge-update.out
@@ -37,13 +37,22 @@ step merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a'
+  RETURNING merge_action(), t.*;
+
+merge_action|key|val                                                   
+------------+---+------------------------------------------------------
+UPDATE      |  3|setup1 updated by merge1 source not matched by merge2a
+INSERT      |  1|merge2a                                               
+(2 rows)
 
 step select2: SELECT * FROM target;
-key|val                     
----+------------------------
-  2|setup1 updated by merge1
-  1|merge2a                 
+key|val                                                   
+---+------------------------------------------------------
+  3|setup1 updated by merge1 source not matched by merge2a
+  1|merge2a                                               
 (2 rows)
 
 step c2: COMMIT;
@@ -86,15 +95,24 @@ step merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a'
+  RETURNING merge_action(), t.*;
  <waiting ...>
 step c1: COMMIT;
 step merge2a: <... completed>
+merge_action|key|val                                                   
+------------+---+------------------------------------------------------
+UPDATE      |  3|setup1 updated by merge1 source not matched by merge2a
+INSERT      |  1|merge2a                                               
+(2 rows)
+
 step select2: SELECT * FROM target;
-key|val                     
----+------------------------
-  2|setup1 updated by merge1
-  1|merge2a                 
+key|val                                                   
+---+------------------------------------------------------
+  3|setup1 updated by merge1 source not matched by merge2a
+  1|merge2a                                               
 (2 rows)
 
 step c2: COMMIT;
@@ -116,10 +134,18 @@ step merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a'
+  RETURNING merge_action(), t.*;
  <waiting ...>
 step a1: ABORT;
 step merge2a: <... completed>
+merge_action|key|val                      
+------------+---+-------------------------
+UPDATE      |  2|setup1 updated by merge2a
+(1 row)
+
 step select2: SELECT * FROM target;
 key|val                      
 ---+-------------------------
@@ -205,15 +231,24 @@ step pa_merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a'
+  RETURNING merge_action(), t.*;
  <waiting ...>
 step c1: COMMIT;
 step pa_merge2a: <... completed>
+merge_action|key|val                                               
+------------+---+--------------------------------------------------
+UPDATE      |  2|initial updated by pa_merge1 updated by pa_merge2a
+UPDATE      |  3|initial source not matched by pa_merge2a          
+(2 rows)
+
 step pa_select2: SELECT * FROM pa_target;
 key|val                                               
 ---+--------------------------------------------------
-  2|initial                                           
   2|initial updated by pa_merge1 updated by pa_merge2a
+  3|initial source not matched by pa_merge2a          
 (2 rows)
 
 step c2: COMMIT;
@@ -235,7 +270,10 @@ step pa_merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a'
+  RETURNING merge_action(), t.*;
  <waiting ...>
 step c1: COMMIT;
 step pa_merge2a: <... completed>
@@ -262,14 +300,24 @@ step pa_merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a'
+  RETURNING merge_action(), t.*;
+
+merge_action|key|val                                                          
+------------+---+-------------------------------------------------------------
+UPDATE      |  3|initial source not matched by pa_merge2a                     
+UPDATE      |  3|initial updated by pa_merge2 source not matched by pa_merge2a
+INSERT      |  1|pa_merge2a                                                   
+(3 rows)
 
 step pa_select2: SELECT * FROM pa_target;
-key|val                         
----+----------------------------
-  1|pa_merge2a                  
-  2|initial                     
-  2|initial updated by pa_merge2
+key|val                                                          
+---+-------------------------------------------------------------
+  1|pa_merge2a                                                   
+  3|initial source not matched by pa_merge2a                     
+  3|initial updated by pa_merge2 source not matched by pa_merge2a
 (3 rows)
 
 step c2: COMMIT;
diff --git a/src/test/isolation/specs/merge-update.spec b/src/test/isolation/specs/merge-update.spec
new file mode 100644
index 3ccd466..a33dcdb
--- a/src/test/isolation/specs/merge-update.spec
+++ b/src/test/isolation/specs/merge-update.spec
@@ -92,7 +92,10 @@ step "merge2a"
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a'
+  RETURNING merge_action(), t.*;
 }
 step "merge2b"
 {
@@ -122,7 +125,10 @@ step "pa_merge2a"
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a'
+  RETURNING merge_action(), t.*;
 }
 # MERGE proceeds only if 'val' unchanged
 step "pa_merge2b_when"
diff --git a/src/test/regress/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index 07561f0..59035a7
--- a/src/test/regress/expected/merge.out
+++ b/src/test/regress/expected/merge.out
@@ -72,6 +72,15 @@ WHEN MATCHED THEN
 ERROR:  syntax error at or near "INSERT"
 LINE 5:  INSERT DEFAULT VALUES;
          ^
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
+ERROR:  syntax error at or near "INSERT"
+LINE 5:  INSERT DEFAULT VALUES;
+         ^
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -108,6 +117,15 @@ WHEN NOT MATCHED THEN
 ERROR:  syntax error at or near "UPDATE"
 LINE 5:  UPDATE SET balance = 0;
          ^
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
+ERROR:  syntax error at or near "UPDATE"
+LINE 5:  UPDATE SET balance = 0;
+         ^
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -270,6 +288,31 @@ SELECT * FROM target ORDER BY tid;
 (4 rows)
 
 ROLLBACK;
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta)
+RETURNING merge_action(), t.*;
+ merge_action | tid | balance 
+--------------+-----+---------
+ DELETE       |   1 |      10
+ DELETE       |   2 |      20
+ DELETE       |   3 |      30
+ INSERT       |   4 |      40
+(4 rows)
+
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   4 |      40
+(1 row)
+
+ROLLBACK;
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -737,6 +780,19 @@ SELECT * FROM wq_target;
    1 |      -1
 (1 row)
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+ERROR:  invalid reference to FROM-clause entry for table "s"
+LINE 3: WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+                                       ^
+DETAIL:  There is an entry for table "s", but it cannot be referenced from this part of the query.
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
  balance | sid 
@@ -922,6 +978,54 @@ SELECT * FROM target ORDER BY tid;
 (3 rows)
 
 ROLLBACK;
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+RETURNING merge_action(), t.*;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE DELETE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  BEFORE INSERT ROW trigger row: (4,40)
+NOTICE:  BEFORE DELETE ROW trigger row: (2,20)
+NOTICE:  BEFORE UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  AFTER INSERT ROW trigger row: (4,40)
+NOTICE:  AFTER DELETE ROW trigger row: (2,20)
+NOTICE:  AFTER UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER DELETE STATEMENT trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+ merge_action | tid | balance 
+--------------+-----+---------
+ UPDATE       |   3 |      10
+ INSERT       |   4 |      40
+ DELETE       |   2 |      20
+ UPDATE       |   1 |       0
+(4 rows)
+
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |       0
+   3 |      10
+   4 |      40
+(3 rows)
+
+ROLLBACK;
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -1636,6 +1740,50 @@ WHEN NOT MATCHED AND s.a < 20 THEN
                ->  Seq Scan on ex_mtarget t (actual rows=49 loops=1)
 (12 rows)
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=54
+   ->  Merge Left Join (actual rows=54 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=100
+   ->  Merge Full Join (actual rows=100 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
@@ -1765,7 +1913,7 @@ CREATE TABLE pa_source (sid integer, del
 -- insert many rows to the source table
 INSERT INTO pa_source SELECT id, id * 10  FROM generate_series(1,14) AS id;
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 -- try simple MERGE
 BEGIN;
 MERGE INTO pa_target t
@@ -1774,10 +1922,12 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
    3 |     330 | initial updated by merge
@@ -1792,7 +1942,8 @@ SELECT * FROM pa_target ORDER BY tid;
   12 |     120 | inserted by merge
   13 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+  15 |    1500 | initial not matched by source
+(15 rows)
 
 ROLLBACK;
 -- same with a constant qual
@@ -1803,31 +1954,34 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
+   3 |     300 | initial not matched by source
    3 |      30 | inserted by merge
-   3 |     300 | initial
    4 |      40 | inserted by merge
-   5 |     500 | initial
+   5 |     500 | initial not matched by source
    5 |      50 | inserted by merge
    6 |      60 | inserted by merge
-   7 |     700 | initial
+   7 |     700 | initial not matched by source
    7 |      70 | inserted by merge
    8 |      80 | inserted by merge
+   9 |     900 | initial not matched by source
    9 |      90 | inserted by merge
-   9 |     900 | initial
   10 |     100 | inserted by merge
-  11 |    1100 | initial
+  11 |    1100 | initial not matched by source
   11 |     110 | inserted by merge
   12 |     120 | inserted by merge
-  13 |    1300 | initial
+  13 |    1300 | initial not matched by source
   13 |     130 | inserted by merge
   14 |     140 | inserted by merge
-(20 rows)
+  15 |    1500 | initial not matched by source
+(21 rows)
 
 ROLLBACK;
 -- try updating the partition key column
@@ -1842,7 +1996,9 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 IF FOUND THEN
   GET DIAGNOSTICS result := ROW_COUNT;
 END IF;
@@ -1852,27 +2008,28 @@ $$;
 SELECT merge_func();
  merge_func 
 ------------
-         14
+         15
 (1 row)
 
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
+   1 |    1500 | initial not matched by source
    2 |     110 | initial updated by merge
    2 |      20 | inserted by merge
-   4 |      40 | inserted by merge
    4 |     330 | initial updated by merge
+   4 |      40 | inserted by merge
    6 |     550 | initial updated by merge
    6 |      60 | inserted by merge
-   8 |      80 | inserted by merge
    8 |     770 | initial updated by merge
+   8 |      80 | inserted by merge
   10 |     990 | initial updated by merge
   10 |     100 | inserted by merge
   12 |    1210 | initial updated by merge
   12 |     120 | inserted by merge
   14 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+(15 rows)
 
 ROLLBACK;
 -- update partition key to partition not initially scanned
@@ -1898,7 +2055,8 @@ SELECT * FROM pa_target ORDER BY tid;
    9 |     900 | initial
   11 |    1100 | initial
   13 |    1300 | initial
-(7 rows)
+  15 |    1500 | initial
+(8 rows)
 
 ROLLBACK;
 DROP TABLE pa_target CASCADE;
@@ -1920,7 +2078,7 @@ ALTER TABLE pa_target ATTACH PARTITION p
 ALTER TABLE pa_target ATTACH PARTITION part3 FOR VALUES IN (3,8,9);
 ALTER TABLE pa_target ATTACH PARTITION part4 DEFAULT;
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 -- try simple MERGE
 BEGIN;
 DO $$
@@ -1933,15 +2091,17 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 14
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 15
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
    3 |     330 | initial updated by merge
@@ -1956,7 +2116,8 @@ SELECT * FROM pa_target ORDER BY tid;
   12 |     120 | inserted by merge
   13 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+  15 |    1500 | initial not matched by source
+(15 rows)
 
 ROLLBACK;
 -- same with a constant qual
@@ -1968,29 +2129,32 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
+   3 |     300 | initial not matched by source
    3 |      30 | inserted by merge
-   3 |     300 | initial
    4 |      40 | inserted by merge
    6 |      60 | inserted by merge
-   7 |     700 | initial
+   7 |     700 | initial not matched by source
    7 |      70 | inserted by merge
    8 |      80 | inserted by merge
-   9 |     900 | initial
+   9 |     900 | initial not matched by source
    9 |      90 | inserted by merge
   10 |     100 | inserted by merge
+  11 |    1100 | initial not matched by source
   11 |     110 | inserted by merge
-  11 |    1100 | initial
   12 |     120 | inserted by merge
-  13 |    1300 | initial
+  13 |    1300 | initial not matched by source
   13 |     130 | inserted by merge
   14 |     140 | inserted by merge
-(18 rows)
+  15 |    1500 | initial not matched by source
+(19 rows)
 
 ROLLBACK;
 -- try updating the partition key column
@@ -2005,30 +2169,33 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 14
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 15
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
+   1 |    1500 | initial not matched by source
    2 |     110 | initial updated by merge
    2 |      20 | inserted by merge
-   4 |      40 | inserted by merge
    4 |     330 | initial updated by merge
+   4 |      40 | inserted by merge
    6 |     550 | initial updated by merge
    6 |      60 | inserted by merge
-   8 |      80 | inserted by merge
    8 |     770 | initial updated by merge
+   8 |      80 | inserted by merge
   10 |     990 | initial updated by merge
   10 |     100 | inserted by merge
   12 |    1210 | initial updated by merge
   12 |     120 | inserted by merge
   14 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+(15 rows)
 
 ROLLBACK;
 -- as above, but blocked by BEFORE DELETE ROW trigger
@@ -2047,15 +2214,17 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 10
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 11
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     100 | initial
    2 |      20 | inserted by merge
    3 |     300 | initial
@@ -2070,7 +2239,8 @@ SELECT * FROM pa_target ORDER BY tid;
   12 |     120 | inserted by merge
   14 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+  15 |    1500 | initial not matched by source
+(15 rows)
 
 ROLLBACK;
 -- as above, but blocked by BEFORE INSERT ROW trigger
@@ -2089,19 +2259,22 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 3
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 4
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    6 |     550 | initial updated by merge
   12 |    1210 | initial updated by merge
   14 |    1430 | initial updated by merge
-(3 rows)
+  15 |    1500 | initial not matched by source
+(4 rows)
 
 ROLLBACK;
 -- test RLS enforcement
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
new file mode 100644
index 84e359f..35d4eb6
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -3726,7 +3726,39 @@ BEGIN ATOMIC
      t.data,
      t.filling;
 END
+CREATE FUNCTION merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+   USING rule_merge1 s
+   ON (s.a = t.id)
+WHEN NOT MATCHED
+   THEN INSERT (data, id)
+   VALUES (s.a, s.a)
+WHEN MATCHED
+   THEN UPDATE SET data = s.b
+WHEN NOT MATCHED BY SOURCE
+   THEN DELETE;
+END;
+\sf merge_sf_test2
+CREATE OR REPLACE FUNCTION public.merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+    USING rule_merge1 s
+    ON (s.a = t.id)
+    WHEN NOT MATCHED BY TARGET
+     THEN INSERT (data, id)
+      VALUES (s.a, s.a)
+    WHEN MATCHED
+     THEN UPDATE SET data = s.b
+    WHEN NOT MATCHED BY SOURCE
+     THEN DELETE;
+END
 DROP FUNCTION merge_sf_test;
+DROP FUNCTION merge_sf_test2;
 DROP TABLE sf_target;
 --
 -- Test enabling/disabling
diff --git a/src/test/regress/expected/updatable_views.out b/src/test/regress/expected/updatable_views.out
new file mode 100644
index 1062c34..3913674
--- a/src/test/regress/expected/updatable_views.out
+++ b/src/test/regress/expected/updatable_views.out
@@ -499,6 +499,32 @@ SELECT * FROM base_tbl ORDER BY a;
   5 | Unspecified
 (6 rows)
 
+MERGE INTO rw_view1 t
+  USING (VALUES (0, 'R0'), (1, 'R1'),
+                (2, 'R2'), (3, 'R3')) AS v(a,b) ON t.a = v.a
+  WHEN MATCHED AND t.a <= 1 THEN UPDATE SET b = v.b
+  WHEN MATCHED THEN DELETE
+  WHEN NOT MATCHED BY SOURCE THEN DELETE
+  WHEN NOT MATCHED AND a > 0 THEN INSERT (a) VALUES (v.a)
+  RETURNING merge_action(), v.*, t.*;
+ merge_action | a | b  | a |      b      
+--------------+---+----+---+-------------
+ UPDATE       | 1 | R1 | 1 | R1
+ DELETE       |   |    | 5 | Unspecified
+ DELETE       | 2 | R2 | 2 | Unspecified
+ INSERT       | 3 | R3 | 3 | Unspecified
+(4 rows)
+
+SELECT * FROM base_tbl ORDER BY a;
+ a  |      b      
+----+-------------
+ -2 | Row -2
+ -1 | Row -1
+  0 | Row 0
+  1 | R1
+  3 | Unspecified
+(5 rows)
+
 EXPLAIN (costs off) UPDATE rw_view1 SET a=6 WHERE a=5;
                     QUERY PLAN                    
 --------------------------------------------------
@@ -545,6 +571,23 @@ MERGE INTO rw_view1 t
 EXPLAIN (costs off)
 MERGE INTO rw_view1 t
   USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
+  WHEN NOT MATCHED BY SOURCE THEN DELETE;
+                            QUERY PLAN                             
+-------------------------------------------------------------------
+ Merge on base_tbl
+   ->  Hash Left Join
+         Hash Cond: (base_tbl.a = generate_series.generate_series)
+         ->  Bitmap Heap Scan on base_tbl
+               Recheck Cond: (a > 0)
+               ->  Bitmap Index Scan on base_tbl_pkey
+                     Index Cond: (a > 0)
+         ->  Hash
+               ->  Function Scan on generate_series
+(9 rows)
+
+EXPLAIN (costs off)
+MERGE INTO rw_view1 t
+  USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
   WHEN NOT MATCHED THEN INSERT (a) VALUES (s.a);
                             QUERY PLAN                             
 -------------------------------------------------------------------
@@ -656,6 +699,29 @@ SELECT * FROM rw_view2 ORDER BY aaa;
    5 | Unspecified
 (3 rows)
 
+MERGE INTO rw_view2 t
+  USING (VALUES (4, 'r4'), (5, 'r5'), (6, 'r6')) AS v(a,b) ON aaa = v.a
+  WHEN MATCHED AND aaa = 4 THEN DELETE
+  WHEN MATCHED THEN UPDATE SET bbb = v.b
+  WHEN NOT MATCHED THEN INSERT (aaa) VALUES (v.a)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET bbb = 'Not matched by source'
+  RETURNING merge_action(), v.*, t.*;
+ merge_action | a | b  | aaa |          bbb          
+--------------+---+----+-----+-----------------------
+ UPDATE       |   |    |   1 | Not matched by source
+ DELETE       | 4 | r4 |   4 | R4
+ UPDATE       | 5 | r5 |   5 | r5
+ INSERT       | 6 | r6 |   6 | Unspecified
+(4 rows)
+
+SELECT * FROM rw_view2 ORDER BY aaa;
+ aaa |          bbb          
+-----+-----------------------
+   1 | Not matched by source
+   5 | r5
+   6 | Unspecified
+(3 rows)
+
 EXPLAIN (costs off) UPDATE rw_view2 SET aaa=5 WHERE aaa=4;
                        QUERY PLAN                       
 --------------------------------------------------------
@@ -1106,6 +1172,30 @@ SELECT * FROM base_tbl ORDER BY a;
   3 | R3
 (5 rows)
 
+MERGE INTO rw_view2 t
+  USING (SELECT x, 'r'||x FROM generate_series(0,2) x) AS s(a,b) ON t.a = s.a
+  WHEN MATCHED THEN UPDATE SET b = s.b
+  WHEN NOT MATCHED AND s.a > 0 THEN INSERT VALUES (s.a, s.b)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET b = 'Not matched by source'
+  RETURNING merge_action(), s.*, t.*;
+ merge_action | a | b  | a |           b           
+--------------+---+----+---+-----------------------
+ UPDATE       | 2 | r2 | 2 | r2
+ UPDATE       |   |    | 3 | Not matched by source
+ INSERT       | 1 | r1 | 1 | r1
+(3 rows)
+
+SELECT * FROM base_tbl ORDER BY a;
+ a  |           b           
+----+-----------------------
+ -2 | Row -2
+ -1 | Row -1
+  0 | Row 0
+  1 | r1
+  2 | r2
+  3 | Not matched by source
+(6 rows)
+
 EXPLAIN (costs off) UPDATE rw_view2 SET a=3 WHERE a=2;
                         QUERY PLAN                        
 ----------------------------------------------------------
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index 875cf6f..3d5d854
--- a/src/test/regress/sql/merge.sql
+++ b/src/test/regress/sql/merge.sql
@@ -53,6 +53,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN MATCHED THEN
 	INSERT DEFAULT VALUES;
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -77,6 +83,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN NOT MATCHED THEN
 	UPDATE SET balance = 0;
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -214,6 +226,19 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta)
+RETURNING merge_action(), t.*;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -498,6 +523,17 @@ WHEN NOT MATCHED AND s.balance = 100 THE
 	INSERT (tid) VALUES (s.sid);
 SELECT * FROM wq_target;
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
+
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
 MERGE INTO wq_target t
@@ -625,6 +661,26 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+RETURNING merge_action(), t.*;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -1061,6 +1117,20 @@ WHEN MATCHED AND t.a >= 30 AND t.a <= 40
 WHEN NOT MATCHED AND s.a < 20 THEN
 	INSERT VALUES (a, b)');
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
@@ -1133,7 +1203,7 @@ CREATE TABLE pa_source (sid integer, del
 -- insert many rows to the source table
 INSERT INTO pa_source SELECT id, id * 10  FROM generate_series(1,14) AS id;
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 
 -- try simple MERGE
 BEGIN;
@@ -1143,8 +1213,10 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- same with a constant qual
@@ -1155,8 +1227,10 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- try updating the partition key column
@@ -1171,7 +1245,9 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 IF FOUND THEN
   GET DIAGNOSTICS result := ROW_COUNT;
 END IF;
@@ -1179,7 +1255,7 @@ RETURN result;
 END;
 $$;
 SELECT merge_func();
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- update partition key to partition not initially scanned
@@ -1216,7 +1292,7 @@ ALTER TABLE pa_target ATTACH PARTITION p
 ALTER TABLE pa_target ATTACH PARTITION part4 DEFAULT;
 
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 
 -- try simple MERGE
 BEGIN;
@@ -1230,12 +1306,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- same with a constant qual
@@ -1247,8 +1325,10 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- try updating the partition key column
@@ -1263,12 +1343,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- as above, but blocked by BEFORE DELETE ROW trigger
@@ -1287,12 +1369,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- as above, but blocked by BEFORE INSERT ROW trigger
@@ -1311,12 +1395,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- test RLS enforcement
diff --git a/src/test/regress/sql/rules.sql b/src/test/regress/sql/rules.sql
new file mode 100644
index 27340ba..4a5fa50
--- a/src/test/regress/sql/rules.sql
+++ b/src/test/regress/sql/rules.sql
@@ -1338,7 +1338,26 @@ END;
 
 \sf merge_sf_test
 
+CREATE FUNCTION merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+   USING rule_merge1 s
+   ON (s.a = t.id)
+WHEN NOT MATCHED
+   THEN INSERT (data, id)
+   VALUES (s.a, s.a)
+WHEN MATCHED
+   THEN UPDATE SET data = s.b
+WHEN NOT MATCHED BY SOURCE
+   THEN DELETE;
+END;
+
+\sf merge_sf_test2
+
 DROP FUNCTION merge_sf_test;
+DROP FUNCTION merge_sf_test2;
 DROP TABLE sf_target;
 
 --
diff --git a/src/test/regress/sql/updatable_views.sql b/src/test/regress/sql/updatable_views.sql
new file mode 100644
index afdf331..e0ab923
--- a/src/test/regress/sql/updatable_views.sql
+++ b/src/test/regress/sql/updatable_views.sql
@@ -179,6 +179,16 @@ MERGE INTO rw_view1 t
   RETURNING merge_action(), v.*, t.*;
 SELECT * FROM base_tbl ORDER BY a;
 
+MERGE INTO rw_view1 t
+  USING (VALUES (0, 'R0'), (1, 'R1'),
+                (2, 'R2'), (3, 'R3')) AS v(a,b) ON t.a = v.a
+  WHEN MATCHED AND t.a <= 1 THEN UPDATE SET b = v.b
+  WHEN MATCHED THEN DELETE
+  WHEN NOT MATCHED BY SOURCE THEN DELETE
+  WHEN NOT MATCHED AND a > 0 THEN INSERT (a) VALUES (v.a)
+  RETURNING merge_action(), v.*, t.*;
+SELECT * FROM base_tbl ORDER BY a;
+
 EXPLAIN (costs off) UPDATE rw_view1 SET a=6 WHERE a=5;
 EXPLAIN (costs off) DELETE FROM rw_view1 WHERE a=5;
 
@@ -194,6 +204,11 @@ MERGE INTO rw_view1 t
 EXPLAIN (costs off)
 MERGE INTO rw_view1 t
   USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
+  WHEN NOT MATCHED BY SOURCE THEN DELETE;
+
+EXPLAIN (costs off)
+MERGE INTO rw_view1 t
+  USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
   WHEN NOT MATCHED THEN INSERT (a) VALUES (s.a);
 
 -- it's still updatable if we add a DO ALSO rule
@@ -251,6 +266,15 @@ MERGE INTO rw_view2 t
   RETURNING merge_action(), v.*, t.*;
 SELECT * FROM rw_view2 ORDER BY aaa;
 
+MERGE INTO rw_view2 t
+  USING (VALUES (4, 'r4'), (5, 'r5'), (6, 'r6')) AS v(a,b) ON aaa = v.a
+  WHEN MATCHED AND aaa = 4 THEN DELETE
+  WHEN MATCHED THEN UPDATE SET bbb = v.b
+  WHEN NOT MATCHED THEN INSERT (aaa) VALUES (v.a)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET bbb = 'Not matched by source'
+  RETURNING merge_action(), v.*, t.*;
+SELECT * FROM rw_view2 ORDER BY aaa;
+
 EXPLAIN (costs off) UPDATE rw_view2 SET aaa=5 WHERE aaa=4;
 EXPLAIN (costs off) DELETE FROM rw_view2 WHERE aaa=4;
 
@@ -464,6 +488,14 @@ MERGE INTO rw_view2 t
   RETURNING merge_action(), s.*, t.*;
 SELECT * FROM base_tbl ORDER BY a;
 
+MERGE INTO rw_view2 t
+  USING (SELECT x, 'r'||x FROM generate_series(0,2) x) AS s(a,b) ON t.a = s.a
+  WHEN MATCHED THEN UPDATE SET b = s.b
+  WHEN NOT MATCHED AND s.a > 0 THEN INSERT VALUES (s.a, s.b)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET b = 'Not matched by source'
+  RETURNING merge_action(), s.*, t.*;
+SELECT * FROM base_tbl ORDER BY a;
+
 EXPLAIN (costs off) UPDATE rw_view2 SET a=3 WHERE a=2;
 EXPLAIN (costs off) DELETE FROM rw_view2 WHERE a=2;
 
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
new file mode 100644
index 6ca93b1..f7b70db
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1575,6 +1575,7 @@ MergeAppendState
 MergeJoin
 MergeJoinClause
 MergeJoinState
+MergeMatchKind
 MergePath
 MergeScanSelCache
 MergeStmt

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
new file mode 100644
index f8f83d4..380d0c9
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -394,10 +394,14 @@
     conditions for each action are re-evaluated on the updated version of
     the row, starting from the first action, even if the action that had
     originally matched appears later in the list of actions.
-    On the other hand, if the row is concurrently updated or deleted so
-    that the join condition fails, then <command>MERGE</command> will
-    evaluate the condition's <literal>NOT MATCHED</literal> actions next,
-    and execute the first one that succeeds.
+    On the other hand, if the row is concurrently updated so that the join
+    condition fails, then <command>MERGE</command> will evaluate the
+    command's <literal>NOT MATCHED BY SOURCE</literal> and
+    <literal>NOT MATCHED [BY TARGET]</literal> actions next, and execute
+    the first one of each kind that succeeds.
+    If the row is concurrently deleted, then <command>MERGE</command>
+    will evaluate the command's <literal>NOT MATCHED [BY TARGET]</literal>
+    actions, and execute the first one that succeeds.
     If <command>MERGE</command> attempts an <command>INSERT</command>
     and a unique index is present and a duplicate row is concurrently
     inserted, then a uniqueness violation error is raised;
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
new file mode 100644
index 44e5ec0..16f0aa9
--- a/doc/src/sgml/ref/merge.sgml
+++ b/doc/src/sgml/ref/merge.sgml
@@ -34,7 +34,8 @@ USING <replaceable class="parameter">dat
 <phrase>and <replaceable class="parameter">when_clause</replaceable> is:</phrase>
 
 { WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
-  WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
+  WHEN NOT MATCHED BY SOURCE [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> | DO NOTHING } |
+  WHEN NOT MATCHED [BY TARGET] [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING } }
 
 <phrase>and <replaceable class="parameter">merge_insert</replaceable> is:</phrase>
 
@@ -73,7 +74,9 @@ DELETE
    from <replaceable class="parameter">data_source</replaceable> to
    the target table
    producing zero or more candidate change rows.  For each candidate change
-   row, the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal>
+   row, the status of <literal>MATCHED</literal>,
+   <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>
    is set just once, after which <literal>WHEN</literal> clauses are evaluated
    in the order specified.  For each candidate change row, the first clause to
    evaluate as true is executed.  No more than one <literal>WHEN</literal>
@@ -268,18 +271,40 @@ DELETE
       At least one <literal>WHEN</literal> clause is required.
      </para>
      <para>
+      The <literal>WHEN</literal> clause may specify <literal>WHEN MATCHED</literal>,
+      <literal>WHEN NOT MATCHED BY SOURCE</literal>, or
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal>.
+      Note that the <acronym>SQL</acronym> standard only defines
+      <literal>WHEN MATCHED</literal> and <literal>WHEN NOT MATCHED</literal>
+      (which is defined to mean no matching target row).
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> is an extension to the
+      <acronym>SQL</acronym> standard, as is the option to append
+      <literal>BY TARGET</literal> to <literal>WHEN NOT MATCHED</literal>, to
+      make its meaning more explicit.
+     </para>
+     <para>
       If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
       and the candidate change row matches a row in the
-      target table,
-      the <literal>WHEN</literal> clause is executed if the
+      <replaceable class="parameter">data_source</replaceable> to a row in the
+      target table, the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
      </para>
      <para>
-      Conversely, if the <literal>WHEN</literal> clause specifies
-      <literal>WHEN NOT MATCHED</literal>
-      and the candidate change row does not match a row in the
-      target table,
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> and the candidate change
+      row represents a row in the target table that does not match a row in the
+      <replaceable class="parameter">data_source</replaceable>, the
+      <literal>WHEN</literal> clause is executed if the
+      <replaceable class="parameter">condition</replaceable> is
+      absent or it evaluates to <literal>true</literal>.
+     </para>
+     <para>
+      If the <literal>WHEN</literal> clause specifies
+      <literal>WHEN NOT MATCHED [BY TARGET]</literal> and the candidate change
+      row represents a row in the
+      <replaceable class="parameter">data_source</replaceable> that does not
+      match a row in the target table,
       the <literal>WHEN</literal> clause is executed if the
       <replaceable class="parameter">condition</replaceable> is
       absent or it evaluates to <literal>true</literal>.
@@ -299,7 +324,10 @@ DELETE
      <para>
       A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
       in both the source and the target relations. A condition on a
-      <literal>WHEN NOT MATCHED</literal> clause can only refer to columns from
+      <literal>WHEN NOT MATCHED BY SOURCE</literal> clause can only refer to
+      columns from the target relation, since by definition there is no matching
+      source row. A condition on a <literal>WHEN NOT MATCHED [BY TARGET]</literal>
+      clause can only refer to columns from
       the source relation, since by definition there is no matching target row.
       Only the system attributes from the target table are accessible.
      </para>
@@ -423,8 +451,10 @@ DELETE
       <literal>WHEN MATCHED</literal> clause, the expression can use values
       from the original row in the target table, and values from the
       <replaceable class="parameter">data_source</replaceable> row.
-      If used in a <literal>WHEN NOT MATCHED</literal> clause, the
-      expression can use values from the
+      If used in a <literal>WHEN NOT MATCHED BY SOURCE</literal> clause, the
+      expression can only use values from the original row in the target table.
+      If used in a <literal>WHEN NOT MATCHED [BY TARGET]</literal> clause, the
+      expression can only use values from the
       <replaceable class="parameter">data_source</replaceable> row.
      </para>
     </listitem>
@@ -535,8 +565,9 @@ MERGE <replaceable class="parameter">tot
        <orderedlist>
         <listitem>
          <para>
-          Evaluate whether each row is <literal>MATCHED</literal> or
-          <literal>NOT MATCHED</literal>.
+          Evaluate whether each row is <literal>MATCHED</literal>,
+          <literal>NOT MATCHED BY SOURCE</literal>, or
+          <literal>NOT MATCHED [BY TARGET]</literal>.
          </para>
         </listitem>
         <listitem>
@@ -615,7 +646,8 @@ MERGE <replaceable class="parameter">tot
   <para>
    If a <literal>WHEN</literal> clause omits an <literal>AND</literal>
    sub-clause, it becomes the final reachable clause of that
-   kind (<literal>MATCHED</literal> or <literal>NOT MATCHED</literal>).
+   kind (<literal>MATCHED</literal>, <literal>NOT MATCHED BY SOURCE</literal>,
+   or <literal>NOT MATCHED [BY TARGET]</literal>).
    If a later <literal>WHEN</literal> clause of that kind
    is specified it would be provably unreachable and an error is raised.
    If no final reachable clause is specified of either kind, it is
@@ -701,6 +733,23 @@ RETURNING merge_action(), w.*;
    temporary table recently loaded into the database.
   </para>
 
+  <para>
+   Update <literal>wines</literal> based on a replacement wine list, inserting
+   rows for any new stock, updating modified stock entries, and deleting any
+   wines not present in the new list.
+<programlisting>
+MERGE INTO wines w
+USING new_wine_list s
+ON s.winename = w.winename
+WHEN NOT MATCHED BY TARGET THEN
+  INSERT VALUES(s.winename, s.stock)
+WHEN MATCHED AND w.stock != s.stock THEN
+  UPDATE SET stock = s.stock
+WHEN NOT MATCHED BY SOURCE THEN
+  DELETE;
+</programlisting>
+  </para>
+
  </refsect1>
 
  <refsect1>
@@ -709,7 +758,9 @@ RETURNING merge_action(), w.*;
     This command conforms to the <acronym>SQL</acronym> standard.
   </para>
    <para>
-    The <literal>WITH</literal> clause, <literal>DO NOTHING</literal> action,
+    The <literal>WITH</literal> clause, <literal>BY SOURCE</literal> and
+    <literal>BY TARGET</literal> qualifiers to
+    <literal>WHEN NOT MATCHED</literal>, <literal>DO NOTHING</literal> action,
     and <literal>RETURNING</literal> clause are extensions to the
     <acronym>SQL</acronym> standard.
   </para>
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
new file mode 100644
index 7eb1f7d..4d7c92d
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -1251,8 +1251,10 @@ InitResultRelInfo(ResultRelInfo *resultR
 	resultRelInfo->ri_ReturningSlot = NULL;
 	resultRelInfo->ri_TrigOldSlot = NULL;
 	resultRelInfo->ri_TrigNewSlot = NULL;
-	resultRelInfo->ri_matchedMergeAction = NIL;
-	resultRelInfo->ri_notMatchedMergeAction = NIL;
+	resultRelInfo->ri_MergeActions[MERGE_WHEN_MATCHED] = NIL;
+	resultRelInfo->ri_MergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = NIL;
+	resultRelInfo->ri_MergeActions[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = NIL;
+	resultRelInfo->ri_MergeJoinCondition = NULL;
 
 	/*
 	 * Only ExecInitPartitionInfo() and ExecInitPartitionDispatchInfo() pass
diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
new file mode 100644
index 64fcb01..f511092
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -880,6 +880,7 @@ ExecInitPartitionInfo(ModifyTableState *
 		List	   *firstMergeActionList = linitial(node->mergeActionLists);
 		ListCell   *lc;
 		ExprContext *econtext = mtstate->ps.ps_ExprContext;
+		Node	   *joinCondition;
 
 		if (part_attmap == NULL)
 			part_attmap =
@@ -890,23 +891,31 @@ ExecInitPartitionInfo(ModifyTableState *
 		if (unlikely(!leaf_part_rri->ri_projectNewInfoValid))
 			ExecInitMergeTupleSlots(mtstate, leaf_part_rri);
 
+		/* Initialize state for join condition-checking. */
+		joinCondition =
+			map_variable_attnos(linitial(node->mergeJoinConditions),
+								firstVarno, 0,
+								part_attmap,
+								RelationGetForm(partrel)->reltype,
+								&found_whole_row);
+		/* We ignore the value of found_whole_row. */
+		leaf_part_rri->ri_MergeJoinCondition =
+			ExecInitQual((List *) joinCondition, &mtstate->ps);
+
 		foreach(lc, firstMergeActionList)
 		{
 			/* Make a copy for this relation to be safe.  */
 			MergeAction *action = copyObject(lfirst(lc));
 			MergeActionState *action_state;
-			List	  **list;
 
 			/* Generate the action's state for this relation */
 			action_state = makeNode(MergeActionState);
 			action_state->mas_action = action;
 
 			/* And put the action in the appropriate list */
-			if (action->matched)
-				list = &leaf_part_rri->ri_matchedMergeAction;
-			else
-				list = &leaf_part_rri->ri_notMatchedMergeAction;
-			*list = lappend(*list, action_state);
+			leaf_part_rri->ri_MergeActions[action->matchKind] =
+				lappend(leaf_part_rri->ri_MergeActions[action->matchKind],
+						action_state);
 
 			switch (action->commandType)
 			{
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
new file mode 100644
index 4abfe82..ff76830
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -24,13 +24,15 @@
  *		values plus row-locating info for UPDATE and MERGE cases, or just the
  *		row-locating info for DELETE cases.
  *
- *		MERGE runs a join between the source relation and the target
- *		table; if any WHEN NOT MATCHED clauses are present, then the
- *		join is an outer join.  In this case, any unmatched tuples will
- *		have NULL row-locating info, and only INSERT can be run. But for
- *		matched tuples, then row-locating info is used to determine the
- *		tuple to UPDATE or DELETE. When all clauses are WHEN MATCHED,
- *		then an inner join is used, so all tuples contain row-locating info.
+ *		MERGE runs a join between the source relation and the target table.
+ *		If any WHEN NOT MATCHED [BY TARGET] clauses are present, then the join
+ *		is an outer join that might output tuples without a matching target
+ *		tuple.  In this case, any unmatched target tuples will have NULL
+ *		row-locating info, and only INSERT can be run.  But for matched
+ *		target tuples, the row-locating info is used to determine the tuple
+ *		to UPDATE or DELETE.  When all clauses are WHEN MATCHED or WHEN NOT
+ *		MATCHED BY SOURCE, all tuples produced by the join will include a
+ *		matching target tuple, so all tuples contain row-locating info.
  *
  *		If the query specifies RETURNING, then the ModifyTable returns a
  *		RETURNING tuple after completing each row insert, update, or delete.
@@ -2714,48 +2716,61 @@ ExecMerge(ModifyTableContext *context, R
 	bool		matched;
 
 	/*-----
-	 * If we are dealing with a WHEN MATCHED case (tupleid or oldtuple is
-	 * valid, depending on whether the result relation is a table or a view),
-	 * we execute the first action for which the additional WHEN MATCHED AND
+	 * If we are dealing with a WHEN MATCHED case, tupleid or oldtuple is
+	 * valid, depending on whether the result relation is a table or a view.
+	 * We execute the first action for which the additional WHEN MATCHED AND
 	 * quals pass.  If an action without quals is found, that action is
 	 * executed.
 	 *
-	 * Similarly, if we are dealing with WHEN NOT MATCHED case, we look at
-	 * the given WHEN NOT MATCHED actions in sequence until one passes.
+	 * Similarly, in the WHEN NOT MATCHED BY SOURCE case, tupleid or oldtuple
+	 * is valid, and we look at the given WHEN NOT MATCHED BY SOURCE actions
+	 * in sequence until one passes.  This is almost identical to the WHEN
+	 * MATCHED case, and both cases are handled by ExecMergeMatched().
+	 *
+	 * Finally, in the WHEN NOT MATCHED [BY TARGET] case, both tupleid and
+	 * oldtuple are invalid, and we look at the given WHEN NOT MATCHED [BY
+	 * TARGET] actions in sequence until one passes.
 	 *
 	 * Things get interesting in case of concurrent update/delete of the
 	 * target tuple. Such concurrent update/delete is detected while we are
-	 * executing a WHEN MATCHED action.
+	 * executing a WHEN MATCHED or WHEN NOT MATCHED BY SOURCE action.
 	 *
 	 * A concurrent update can:
 	 *
 	 * 1. modify the target tuple so that it no longer satisfies the
-	 *    additional quals attached to the current WHEN MATCHED action
+	 *    additional quals attached to the current WHEN MATCHED or WHEN NOT
+	 *    MATCHED BY SOURCE action, but still satisfies the join quals.
 	 *
-	 *    In this case, we are still dealing with a WHEN MATCHED case.
-	 *    We recheck the list of WHEN MATCHED actions from the start and
-	 *    choose the first one that satisfies the new target tuple.
+	 *    In this case, we are still dealing with the same kind of match
+	 *    (MATCHED or NOT MATCHED BY SOURCE).  We recheck the same list of
+	 *    actions from the start and choose the first one that satisfies the
+	 *    new target tuple.
 	 *
 	 * 2. modify the target tuple so that the join quals no longer pass and
-	 *    hence the source tuple no longer has a match.
+	 *    hence the source and target tuples no longer match.
 	 *
-	 *    In this case, the source tuple no longer matches the target tuple,
-	 *    so we now instead find a qualifying WHEN NOT MATCHED action to
-	 *    execute.
+	 *    In this case, we are now dealing with a NOT MATCHED case, and we
+	 *    process both WHEN NOT MATCHED BY SOURCE and WHEN NOT MATCHED [BY
+	 *    TARGET] actions.  First ExecMergeMatched() processes the list of
+	 *    WHEN NOT MATCHED BY SOURCE actions in sequence until one passes,
+	 *    then ExecMergeNotMatched() processes any WHEN NOT MATCHED [BY
+	 *    TARGET] actions in sequence until one passes.  Thus we may execute
+	 *    two actions; one of each kind.
 	 *
 	 * XXX Hmmm, what if the updated tuple would now match one that was
 	 * considered NOT MATCHED so far?
 	 *
-	 * A concurrent delete changes a WHEN MATCHED case to WHEN NOT MATCHED.
+	 * A concurrent delete changes a WHEN MATCHED case to WHEN NOT MATCHED
+	 * [BY TARGET].
 	 *
 	 * ExecMergeMatched takes care of following the update chain and
-	 * re-finding the qualifying WHEN MATCHED action, as long as the updated
-	 * target tuple still satisfies the join quals, i.e., it remains a WHEN
-	 * MATCHED case. If the tuple gets deleted or the join quals fail, it
-	 * returns and we try ExecMergeNotMatched. Given that ExecMergeMatched
-	 * always make progress by following the update chain and we never switch
-	 * from ExecMergeNotMatched to ExecMergeMatched, there is no risk of a
-	 * livelock.
+	 * re-finding the qualifying WHEN MATCHED or WHEN NOT MATCHED BY SOURCE
+	 * action, as long as the target tuple still exists. If the target tuple
+	 * gets deleted or a concurrent update causes the join quals to fail, it
+	 * returns a matched status of false and we call ExecMergeNotMatched.
+	 * Given that ExecMergeMatched always makes progress by following the
+	 * update chain and we never switch from ExecMergeNotMatched to
+	 * ExecMergeMatched, there is no risk of a livelock.
 	 */
 	matched = tupleid != NULL || oldtuple != NULL;
 	if (matched)
@@ -2768,33 +2783,52 @@ ExecMerge(ModifyTableContext *context, R
 	 * "matched" to false, indicating that it no longer matches).
 	 */
 	if (!matched)
-		rslot = ExecMergeNotMatched(context, resultRelInfo, canSetTag);
+	{
+		/*
+		 * If a concurrent update turned a MATCHED case into a NOT MATCHED
+		 * case, and we have both WHEN NOT MATCHED BY SOURCE and WHEN NOT
+		 * MATCHED [BY TARGET] actions, and there is a RETURNING clause,
+		 * ExecMergeMatched() may have already executed a WHEN NOT MATCHED BY
+		 * SOURCE action, and computed the row to return.  If so, we cannot
+		 * execute the WHEN NOT MATCHED [BY TARGET] action now, so mark it as
+		 * pending (to be processed on the next call to ExecModifyTable()).
+		 * Otherwise, just process the action now.
+		 */
+		if (rslot == NULL)
+			rslot = ExecMergeNotMatched(context, resultRelInfo, canSetTag);
+		else
+			context->mtstate->mt_merge_pending_not_matched = context->planSlot;
+	}
 
 	return rslot;
 }
 
 /*
- * Check and execute the first qualifying MATCHED action.  If the target
+ * Check and execute the first qualifying MATCHED or NOT MATCHED BY SOURCE
+ * action, depending on whether the join quals are satisfied.  If the target
  * relation is a table, the current target tuple is identified by tupleid.
  * Otherwise, if the target relation is a view, oldtuple is the current target
  * tuple from the view.
  *
- * We start from the first WHEN MATCHED action and check if the WHEN quals
- * pass, if any. If the WHEN quals for the first action do not pass, we
- * check the second, then the third and so on. If we reach to the end, no
- * action is taken and "matched" is set to true, indicating that no further
- * action is required for this tuple.
+ * We start from the first WHEN MATCHED or WHEN NOT MATCHED BY SOURCE action
+ * and check if the WHEN quals pass, if any. If the WHEN quals for the first
+ * action do not pass, we check the second, then the third and so on. If we
+ * reach the end without finding a qualifying action, we return NULL.
+ * Otherwise, we execute the qualifying action and return its RETURNING
+ * result, if any, or NULL.
  *
- * If we do find a qualifying action, then we attempt to execute the action.
+ * On entry, "*matched" is assumed to be true.  If a concurrent update or
+ * delete is detected that causes the join quals to no longer pass, we set it
+ * to false, indicating that the caller should process any NOT MATCHED [BY
+ * TARGET] actions.
  *
- * If the tuple is concurrently updated, EvalPlanQual is run with the updated
- * tuple to recheck the join quals. Note that the additional quals associated
- * with individual actions are evaluated by this routine via ExecQual, while
- * EvalPlanQual checks for the join quals. If EvalPlanQual tells us that the
- * updated tuple still passes the join quals, then we restart from the first
- * action to look for a qualifying action. Otherwise, "matched" is set to
- * false -- meaning that a NOT MATCHED action must now be executed for the
- * current source tuple.
+ * After a concurrent update, we restart from the first action to look for a
+ * new qualifying action to execute. If the join quals originally passed, and
+ * the concurrent update caused them to no longer pass, then we switch from
+ * the MATCHED to the NOT MATCHED BY SOURCE list of actions before restarting
+ * (and setting "*matched" to false).  As a result we may execute a WHEN NOT
+ * MATCHED BY SOURCE action, and set "*matched" to false, causing the caller
+ * to also execute a WHEN NOT MATCHED [BY TARGET] action.
  */
 static TupleTableSlot *
 ExecMergeMatched(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
@@ -2802,6 +2836,8 @@ ExecMergeMatched(ModifyTableContext *con
 				 bool *matched)
 {
 	ModifyTableState *mtstate = context->mtstate;
+	List	  **mergeActions = resultRelInfo->ri_MergeActions;
+	List	   *actionStates;
 	TupleTableSlot *newslot = NULL;
 	TupleTableSlot *rslot = NULL;
 	EState	   *estate = context->estate;
@@ -2810,54 +2846,58 @@ ExecMergeMatched(ModifyTableContext *con
 	EPQState   *epqstate = &mtstate->mt_epqstate;
 	ListCell   *l;
 
+	/* Expect matched to be true on entry */
+	Assert(*matched == true);
+
 	/*
-	 * If there are no WHEN MATCHED actions, we are done.
+	 * If there are no WHEN MATCHED or WHEN NOT MATCHED BY SOURCE actions, we
+	 * are done.
 	 */
-	if (resultRelInfo->ri_matchedMergeAction == NIL)
-	{
-		*matched = true;
+	if (mergeActions[MERGE_WHEN_MATCHED] == NIL &&
+		mergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] == NIL)
 		return NULL;
-	}
 
 	/*
 	 * Make tuple and any needed join variables available to ExecQual and
 	 * ExecProject. The target's existing tuple is installed in the scantuple.
-	 * Again, this target relation's slot is required only in the case of a
-	 * MATCHED tuple and UPDATE/DELETE actions.
+	 * This target relation's slot is required only in the case of a MATCHED
+	 * or NOT MATCHED BY SOURCE tuple and UPDATE/DELETE actions.
 	 */
 	econtext->ecxt_scantuple = resultRelInfo->ri_oldTupleSlot;
 	econtext->ecxt_innertuple = context->planSlot;
 	econtext->ecxt_outertuple = NULL;
 
 	/*
-	 * This routine is only invoked for matched rows, so we should either have
-	 * the tupleid of the target row, or an old tuple from the target wholerow
-	 * junk attr.
+	 * This routine is only invoked for matched target rows, so we should
+	 * either have the tupleid of the target row, or an old tuple from the
+	 * target wholerow junk attr.
 	 */
 	Assert(tupleid != NULL || oldtuple != NULL);
 	if (oldtuple != NULL)
 		ExecForceStoreHeapTuple(oldtuple, resultRelInfo->ri_oldTupleSlot,
 								false);
-
-lmerge_matched:
+	else if (!table_tuple_fetch_row_version(resultRelInfo->ri_RelationDesc,
+											tupleid,
+											SnapshotAny,
+											resultRelInfo->ri_oldTupleSlot))
+		elog(ERROR, "failed to fetch the target tuple");
 
 	/*
-	 * If passed a tupleid, use it to fetch the old target row.
+	 * Test the join condition.  If it's satisfied, perform a MATCHED action;
+	 * otherwise, perform a NOT MATCHED BY SOURCE action.
 	 *
-	 * We use SnapshotAny for this because we might get called again after
-	 * EvalPlanQual returns us a new tuple, which may not be visible to our
-	 * MVCC snapshot.
+	 * Note that this join condition will be NULL if there are no NOT MATCHED
+	 * BY SOURCE actions --- see transform_MERGE_to_join().  In that case, we
+	 * need only consider MATCHED actions here.
 	 */
-	if (tupleid != NULL)
-	{
-		if (!table_tuple_fetch_row_version(resultRelInfo->ri_RelationDesc,
-										   tupleid,
-										   SnapshotAny,
-										   resultRelInfo->ri_oldTupleSlot))
-			elog(ERROR, "failed to fetch the target tuple");
-	}
+	if (ExecQual(resultRelInfo->ri_MergeJoinCondition, econtext))
+		actionStates = mergeActions[MERGE_WHEN_MATCHED];
+	else
+		actionStates = mergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE];
 
-	foreach(l, resultRelInfo->ri_matchedMergeAction)
+lmerge_matched:
+
+	foreach(l, actionStates)
 	{
 		MergeActionState *relaction = (MergeActionState *) lfirst(l);
 		CmdType		commandType = relaction->mas_action->commandType;
@@ -2912,10 +2952,8 @@ lmerge_matched:
 										tupleid, NULL, newslot, &result))
 				{
 					if (result == TM_Ok)
-					{
-						*matched = true;
 						return NULL;	/* "do nothing" */
-					}
+
 					break;		/* concurrent update/delete */
 				}
 
@@ -2925,10 +2963,7 @@ lmerge_matched:
 				{
 					if (!ExecIRUpdateTriggers(estate, resultRelInfo,
 											  oldtuple, newslot))
-					{
-						*matched = true;
 						return NULL;	/* "do nothing" */
-					}
 				}
 				else
 				{
@@ -2948,7 +2983,6 @@ lmerge_matched:
 					if (updateCxt.crossPartUpdate)
 					{
 						mtstate->mt_merge_updated += 1;
-						*matched = true;
 						return context->cpUpdateReturningSlot;
 					}
 				}
@@ -2967,10 +3001,8 @@ lmerge_matched:
 										NULL, NULL, &result))
 				{
 					if (result == TM_Ok)
-					{
-						*matched = true;
 						return NULL;	/* "do nothing" */
-					}
+
 					break;		/* concurrent update/delete */
 				}
 
@@ -2980,10 +3012,7 @@ lmerge_matched:
 				{
 					if (!ExecIRDeleteTriggers(estate, resultRelInfo,
 											  oldtuple))
-					{
-						*matched = true;
 						return NULL;	/* "do nothing" */
-					}
 				}
 				else
 					result = ExecDeleteAct(context, resultRelInfo, tupleid,
@@ -3003,7 +3032,7 @@ lmerge_matched:
 				break;
 
 			default:
-				elog(ERROR, "unknown action in MERGE WHEN MATCHED clause");
+				elog(ERROR, "unknown action in MERGE WHEN clause");
 		}
 
 		switch (result)
@@ -3060,14 +3089,15 @@ lmerge_matched:
 							 errmsg("could not serialize access due to concurrent delete")));
 
 				/*
-				 * If the tuple was already deleted, return to let caller
-				 * handle it under NOT MATCHED clauses.
+				 * If the tuple was already deleted, set matched to false to
+				 * let caller handle it under NOT MATCHED [BY TARGET] clauses.
 				 */
 				*matched = false;
 				return NULL;
 
 			case TM_Updated:
 				{
+					bool		was_matched;
 					Relation	resultRelationDesc;
 					TupleTableSlot *epqslot,
 							   *inputslot;
@@ -3075,19 +3105,23 @@ lmerge_matched:
 
 					/*
 					 * The target tuple was concurrently updated by some other
-					 * transaction. Run EvalPlanQual() with the new version of
-					 * the tuple. If it does not return a tuple, then we
-					 * switch to the NOT MATCHED list of actions. If it does
-					 * return a tuple and the join qual is still satisfied,
-					 * then we just need to recheck the MATCHED actions,
-					 * starting from the top, and execute the first qualifying
-					 * action.
+					 * transaction.  If we are currently processing a MATCHED
+					 * action, use EvalPlanQual() with the new version of the
+					 * tuple and recheck the join qual, to detect a change
+					 * from the MATCHED to the NOT MATCHED cases.  If we are
+					 * already processing a NOT MATCHED BY SOURCE action, we
+					 * skip this (cannot switch from NOT MATCHED BY SOURCE to
+					 * MATCHED).
 					 */
+					was_matched = relaction->mas_action->matchKind == MERGE_WHEN_MATCHED;
 					resultRelationDesc = resultRelInfo->ri_RelationDesc;
 					lockmode = ExecUpdateLockMode(estate, resultRelInfo);
 
-					inputslot = EvalPlanQualSlot(epqstate, resultRelationDesc,
-												 resultRelInfo->ri_RangeTableIndex);
+					if (was_matched)
+						inputslot = EvalPlanQualSlot(epqstate, resultRelationDesc,
+													 resultRelInfo->ri_RangeTableIndex);
+					else
+						inputslot = resultRelInfo->ri_oldTupleSlot;
 
 					result = table_tuple_lock(resultRelationDesc, tupleid,
 											  estate->es_snapshot,
@@ -3098,34 +3132,9 @@ lmerge_matched:
 					switch (result)
 					{
 						case TM_Ok:
-							epqslot = EvalPlanQual(epqstate,
-												   resultRelationDesc,
-												   resultRelInfo->ri_RangeTableIndex,
-												   inputslot);
 
 							/*
-							 * If we got no tuple, or the tuple we get has a
-							 * NULL ctid, go back to caller: this one is not a
-							 * MATCHED tuple anymore, so they can retry with
-							 * NOT MATCHED actions.
-							 */
-							if (TupIsNull(epqslot))
-							{
-								*matched = false;
-								return NULL;
-							}
-
-							(void) ExecGetJunkAttribute(epqslot,
-														resultRelInfo->ri_RowIdAttNo,
-														&isNull);
-							if (isNull)
-							{
-								*matched = false;
-								return NULL;
-							}
-
-							/*
-							 * When a tuple was updated and migrated to
+							 * If the tuple was updated and migrated to
 							 * another partition concurrently, the current
 							 * MERGE implementation can't follow.  There's
 							 * probably a better way to handle this case, but
@@ -3136,26 +3145,72 @@ lmerge_matched:
 							if (ItemPointerIndicatesMovedPartitions(&context->tmfd.ctid))
 								ereport(ERROR,
 										(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
-										 errmsg("tuple to be deleted was already moved to another partition due to concurrent update")));
+										 errmsg("tuple to be merged was already moved to another partition due to concurrent update")));
 
 							/*
-							 * A non-NULL ctid means that we are still dealing
-							 * with MATCHED case. Restart the loop so that we
-							 * apply all the MATCHED rules again, to ensure
-							 * that the first qualifying WHEN MATCHED action
-							 * is executed.
-							 *
-							 * Update tupleid to that of the new tuple, for
-							 * the refetch we do at the top.
+							 * If this was a MATCHED case, use EvalPlanQual()
+							 * to recheck the join condition.
+							 */
+							if (was_matched)
+							{
+								epqslot = EvalPlanQual(epqstate,
+													   resultRelationDesc,
+													   resultRelInfo->ri_RangeTableIndex,
+													   inputslot);
+
+								/*
+								 * If the subplan didn't return a tuple, then
+								 * we must be dealing with an inner join for
+								 * which the join condition no longer matches.
+								 * This can only happen if there are no NOT
+								 * MATCHED actions, and so there is nothing
+								 * more to do.
+								 */
+								if (TupIsNull(epqslot))
+									return NULL;
+
+								/*
+								 * If we got a NULL ctid from the subplan, the
+								 * join quals no longer pass and we switch to
+								 * the NOT MATCHED BY SOURCE case.
+								 */
+								(void) ExecGetJunkAttribute(epqslot,
+															resultRelInfo->ri_RowIdAttNo,
+															&isNull);
+								if (isNull)
+									*matched = false;
+
+								/*
+								 * Otherwise, recheck the join quals to see if
+								 * we need to switch to the NOT MATCHED BY
+								 * SOURCE case.
+								 */
+								if (!table_tuple_fetch_row_version(resultRelationDesc,
+																   &context->tmfd.ctid,
+																   SnapshotAny,
+																   resultRelInfo->ri_oldTupleSlot))
+									elog(ERROR, "failed to fetch the target tuple");
+
+								if (*matched)
+									*matched = ExecQual(resultRelInfo->ri_MergeJoinCondition,
+														econtext);
+
+								/* Switch lists, if necessary */
+								if (!*matched)
+									actionStates = mergeActions[MERGE_WHEN_NOT_MATCHED_BY_SOURCE];
+							}
+
+							/*
+							 * Loop back and process the MATCHED or NOT
+							 * MATCHED BY SOURCE actions from the start.
 							 */
-							ItemPointerCopy(&context->tmfd.ctid, tupleid);
 							goto lmerge_matched;
 
 						case TM_Deleted:
 
 							/*
 							 * tuple already deleted; tell caller to run NOT
-							 * MATCHED actions
+							 * MATCHED [BY TARGET] actions
 							 */
 							*matched = false;
 							return NULL;
@@ -3239,13 +3294,11 @@ lmerge_matched:
 	/*
 	 * Successfully executed an action or no qualifying action was found.
 	 */
-	*matched = true;
-
 	return rslot;
 }
 
 /*
- * Execute the first qualifying NOT MATCHED action.
+ * Execute the first qualifying NOT MATCHED [BY TARGET] action.
  */
 static TupleTableSlot *
 ExecMergeNotMatched(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
@@ -3253,7 +3306,7 @@ ExecMergeNotMatched(ModifyTableContext *
 {
 	ModifyTableState *mtstate = context->mtstate;
 	ExprContext *econtext = mtstate->ps.ps_ExprContext;
-	List	   *actionStates = NIL;
+	List	   *actionStates;
 	TupleTableSlot *rslot = NULL;
 	ListCell   *l;
 
@@ -3266,7 +3319,7 @@ ExecMergeNotMatched(ModifyTableContext *
 	 * XXX does this mean that we can avoid creating copies of actionStates on
 	 * partitioned tables, for not-matched actions?
 	 */
-	actionStates = resultRelInfo->ri_notMatchedMergeAction;
+	actionStates = resultRelInfo->ri_MergeActions[MERGE_WHEN_NOT_MATCHED_BY_TARGET];
 
 	/*
 	 * Make source tuple available to ExecQual and ExecProject. We don't need
@@ -3360,9 +3413,11 @@ ExecInitMerge(ModifyTableState *mtstate,
 	foreach(lc, node->mergeActionLists)
 	{
 		List	   *mergeActionList = lfirst(lc);
+		Node	   *joinCondition;
 		TupleDesc	relationDesc;
 		ListCell   *l;
 
+		joinCondition = (Node *) list_nth(node->mergeJoinConditions, i);
 		resultRelInfo = mtstate->resultRelInfo + i;
 		i++;
 		relationDesc = RelationGetDescr(resultRelInfo->ri_RelationDesc);
@@ -3371,13 +3426,16 @@ ExecInitMerge(ModifyTableState *mtstate,
 		if (unlikely(!resultRelInfo->ri_projectNewInfoValid))
 			ExecInitMergeTupleSlots(mtstate, resultRelInfo);
 
+		/* initialize state for join condition-checking */
+		resultRelInfo->ri_MergeJoinCondition =
+			ExecInitQual((List *) joinCondition, &mtstate->ps);
+
 		foreach(l, mergeActionList)
 		{
 			MergeAction *action = (MergeAction *) lfirst(l);
 			MergeActionState *action_state;
 			TupleTableSlot *tgtslot;
 			TupleDesc	tgtdesc;
-			List	  **list;
 
 			/*
 			 * Build action merge state for this rel.  (For partitions,
@@ -3389,15 +3447,12 @@ ExecInitMerge(ModifyTableState *mtstate,
 													  &mtstate->ps);
 
 			/*
-			 * We create two lists - one for WHEN MATCHED actions and one for
-			 * WHEN NOT MATCHED actions - and stick the MergeActionState into
-			 * the appropriate list.
+			 * We create three lists - one for each MergeMatchKind - and stick
+			 * the MergeActionState into the appropriate list.
 			 */
-			if (action_state->mas_action->matched)
-				list = &resultRelInfo->ri_matchedMergeAction;
-			else
-				list = &resultRelInfo->ri_notMatchedMergeAction;
-			*list = lappend(*list, action_state);
+			resultRelInfo->ri_MergeActions[action->matchKind] =
+				lappend(resultRelInfo->ri_MergeActions[action->matchKind],
+						action_state);
 
 			switch (action->commandType)
 			{
@@ -3754,6 +3809,31 @@ ExecModifyTable(PlanState *pstate)
 		if (pstate->ps_ExprContext)
 			ResetExprContext(pstate->ps_ExprContext);
 
+		/*
+		 * If there is a pending MERGE ... WHEN NOT MATCHED [BY TARGET] action
+		 * to execute, do so now --- see the comments in ExecMerge().
+		 */
+		if (node->mt_merge_pending_not_matched != NULL)
+		{
+			context.planSlot = node->mt_merge_pending_not_matched;
+
+			slot = ExecMergeNotMatched(&context, node->resultRelInfo,
+									   node->canSetTag);
+
+			/* Clear the pending action */
+			node->mt_merge_pending_not_matched = NULL;
+
+			/*
+			 * If we got a RETURNING result, return it to the caller.  We'll
+			 * continue the work on next call.
+			 */
+			if (slot)
+				return slot;
+
+			continue;			/* continue with the next tuple */
+		}
+
+		/* Fetch the next row from subplan */
 		context.planSlot = ExecProcNode(subplanstate);
 
 		/* No more tuples to process? */
@@ -4139,6 +4219,7 @@ ExecInitModifyTable(ModifyTable *node, E
 	mtstate->resultRelInfo = (ResultRelInfo *)
 		palloc(nrels * sizeof(ResultRelInfo));
 
+	mtstate->mt_merge_pending_not_matched = NULL;
 	mtstate->mt_merge_inserted = 0;
 	mtstate->mt_merge_updated = 0;
 	mtstate->mt_merge_deleted = 0;
diff --git a/src/backend/nodes/nodeFuncs.c b/src/backend/nodes/nodeFuncs.c
new file mode 100644
index 9f1553b..7d37226
--- a/src/backend/nodes/nodeFuncs.c
+++ b/src/backend/nodes/nodeFuncs.c
@@ -2701,6 +2701,8 @@ query_tree_walker_impl(Query *query,
 		return true;
 	if (WALK(query->mergeActionList))
 		return true;
+	if (WALK(query->mergeJoinCondition))
+		return true;
 	if (WALK(query->returningList))
 		return true;
 	if (WALK(query->jointree))
@@ -3752,6 +3754,7 @@ query_tree_mutator_impl(Query *query,
 	MUTATE(query->withCheckOptions, query->withCheckOptions, List *);
 	MUTATE(query->onConflict, query->onConflict, OnConflictExpr *);
 	MUTATE(query->mergeActionList, query->mergeActionList, List *);
+	MUTATE(query->mergeJoinCondition, query->mergeJoinCondition, Node *);
 	MUTATE(query->returningList, query->returningList, List *);
 	MUTATE(query->jointree, query->jointree, FromExpr *);
 	MUTATE(query->setOperations, query->setOperations, Node *);
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
new file mode 100644
index 5f479fc..3b77886
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -312,7 +312,8 @@ static ModifyTable *make_modifytable(Pla
 									 List *updateColnosLists,
 									 List *withCheckOptionLists, List *returningLists,
 									 List *rowMarks, OnConflictExpr *onconflict,
-									 List *mergeActionLists, int epqParam);
+									 List *mergeActionLists, List *mergeJoinConditions,
+									 int epqParam);
 static GatherMerge *create_gather_merge_plan(PlannerInfo *root,
 											 GatherMergePath *best_path);
 
@@ -2836,6 +2837,7 @@ create_modifytable_plan(PlannerInfo *roo
 							best_path->rowMarks,
 							best_path->onconflict,
 							best_path->mergeActionLists,
+							best_path->mergeJoinConditions,
 							best_path->epqParam);
 
 	copy_generic_path_info(&plan->plan, &best_path->path);
@@ -7031,7 +7033,8 @@ make_modifytable(PlannerInfo *root, Plan
 				 List *updateColnosLists,
 				 List *withCheckOptionLists, List *returningLists,
 				 List *rowMarks, OnConflictExpr *onconflict,
-				 List *mergeActionLists, int epqParam)
+				 List *mergeActionLists, List *mergeJoinConditions,
+				 int epqParam)
 {
 	ModifyTable *node = makeNode(ModifyTable);
 	List	   *fdw_private_list;
@@ -7101,6 +7104,7 @@ make_modifytable(PlannerInfo *root, Plan
 	node->returningLists = returningLists;
 	node->rowMarks = rowMarks;
 	node->mergeActionLists = mergeActionLists;
+	node->mergeJoinConditions = mergeJoinConditions;
 	node->epqParam = epqParam;
 
 	/*
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
new file mode 100644
index 5564826..6318b18
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -905,6 +905,9 @@ subquery_planner(PlannerGlobal *glob, Qu
 								  EXPRKIND_QUAL);
 	}
 
+	parse->mergeJoinCondition =
+		preprocess_expression(root, parse->mergeJoinCondition, EXPRKIND_QUAL);
+
 	root->append_rel_list = (List *)
 		preprocess_expression(root, (Node *) root->append_rel_list,
 							  EXPRKIND_APPINFO);
@@ -1787,6 +1790,7 @@ grouping_planner(PlannerInfo *root, doub
 			List	   *withCheckOptionLists = NIL;
 			List	   *returningLists = NIL;
 			List	   *mergeActionLists = NIL;
+			List	   *mergeJoinConditions = NIL;
 			List	   *rowMarks;
 
 			if (bms_membership(root->all_result_relids) == BMS_MULTIPLE)
@@ -1893,6 +1897,19 @@ grouping_planner(PlannerInfo *root, doub
 						mergeActionLists = lappend(mergeActionLists,
 												   mergeActionList);
 					}
+					if (parse->commandType == CMD_MERGE)
+					{
+						Node	   *mergeJoinCondition = parse->mergeJoinCondition;
+
+						if (this_result_rel != top_result_rel)
+							mergeJoinCondition =
+								adjust_appendrel_attrs_multilevel(root,
+																  mergeJoinCondition,
+																  this_result_rel,
+																  top_result_rel);
+						mergeJoinConditions = lappend(mergeJoinConditions,
+													  mergeJoinCondition);
+					}
 				}
 
 				if (resultRelations == NIL)
@@ -1917,6 +1934,8 @@ grouping_planner(PlannerInfo *root, doub
 						returningLists = list_make1(parse->returningList);
 					if (parse->mergeActionList)
 						mergeActionLists = list_make1(parse->mergeActionList);
+					if (parse->commandType == CMD_MERGE)
+						mergeJoinConditions = list_make1(parse->mergeJoinCondition);
 				}
 			}
 			else
@@ -1932,6 +1951,8 @@ grouping_planner(PlannerInfo *root, doub
 					returningLists = list_make1(parse->returningList);
 				if (parse->mergeActionList)
 					mergeActionLists = list_make1(parse->mergeActionList);
+				if (parse->commandType == CMD_MERGE)
+					mergeJoinConditions = list_make1(parse->mergeJoinCondition);
 			}
 
 			/*
@@ -1959,6 +1980,7 @@ grouping_planner(PlannerInfo *root, doub
 										rowMarks,
 										parse->onConflict,
 										mergeActionLists,
+										mergeJoinConditions,
 										assign_special_exec_param(root));
 		}
 
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
new file mode 100644
index 42603db..37abcb4
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -1143,7 +1143,9 @@ set_plan_refs(PlannerInfo *root, Plan *p
 				 */
 				if (splan->mergeActionLists != NIL)
 				{
+					List	   *newMJC = NIL;
 					ListCell   *lca,
+							   *lcj,
 							   *lcr;
 
 					/*
@@ -1164,10 +1166,12 @@ set_plan_refs(PlannerInfo *root, Plan *p
 
 					itlist = build_tlist_index(subplan->targetlist);
 
-					forboth(lca, splan->mergeActionLists,
-							lcr, splan->resultRelations)
+					forthree(lca, splan->mergeActionLists,
+							 lcj, splan->mergeJoinConditions,
+							 lcr, splan->resultRelations)
 					{
 						List	   *mergeActionList = lfirst(lca);
+						Node	   *mergeJoinCondition = lfirst(lcj);
 						Index		resultrel = lfirst_int(lcr);
 
 						foreach(l, mergeActionList)
@@ -1192,7 +1196,19 @@ set_plan_refs(PlannerInfo *root, Plan *p
 																  NRM_EQUAL,
 																  NUM_EXEC_QUAL(plan));
 						}
+
+						/* Fix join condition too. */
+						mergeJoinCondition = (Node *)
+							fix_join_expr(root,
+										  (List *) mergeJoinCondition,
+										  NULL, itlist,
+										  resultrel,
+										  rtoffset,
+										  NRM_EQUAL,
+										  NUM_EXEC_QUAL(plan));
+						newMJC = lappend(newMJC, mergeJoinCondition);
 					}
+					splan->mergeJoinConditions = newMJC;
 				}
 
 				splan->nominalRelation += rtoffset;
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
new file mode 100644
index 300691c..2d8956d
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -153,9 +153,11 @@ transform_MERGE_to_join(Query *parse)
 {
 	RangeTblEntry *joinrte;
 	JoinExpr   *joinexpr;
+	bool		have_action[3];
 	JoinType	jointype;
 	int			joinrti;
 	List	   *vars;
+	RangeTblRef *rtr;
 
 	if (parse->commandType != CMD_MERGE)
 		return;
@@ -164,11 +166,27 @@ transform_MERGE_to_join(Query *parse)
 	vars = NIL;
 
 	/*
-	 * When any WHEN NOT MATCHED THEN INSERT clauses exist, we need to use an
-	 * outer join so that we process all unmatched tuples from the source
-	 * relation.  If none exist, we can use an inner join.
+	 * Work out what kind of join is required.  If there any WHEN NOT MATCHED
+	 * BY SOURCE/TARGET actions, an outer join is required so that we process
+	 * all unmatched tuples from the source and/or target relations.
+	 * Otherwise, we can use an inner join.
 	 */
-	if (parse->mergeUseOuterJoin)
+	have_action[MERGE_WHEN_MATCHED] = false;
+	have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	have_action[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
+
+	foreach_node(MergeAction, action, parse->mergeActionList)
+	{
+		if (action->commandType != CMD_NOTHING)
+			have_action[action->matchKind] = true;
+	}
+
+	if (have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] &&
+		have_action[MERGE_WHEN_NOT_MATCHED_BY_TARGET])
+		jointype = JOIN_FULL;
+	else if (have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE])
+		jointype = JOIN_LEFT;
+	else if (have_action[MERGE_WHEN_NOT_MATCHED_BY_TARGET])
 		jointype = JOIN_RIGHT;
 	else
 		jointype = JOIN_INNER;
@@ -204,16 +222,16 @@ transform_MERGE_to_join(Query *parse)
 	 * trigger-updatable view, it will be the expanded view subquery that we
 	 * need to pull data from.
 	 */
+	rtr = makeNode(RangeTblRef);
+	rtr->rtindex = parse->mergeTargetRelation;
 	joinexpr = makeNode(JoinExpr);
 	joinexpr->jointype = jointype;
 	joinexpr->isNatural = false;
-	joinexpr->larg = (Node *) makeNode(RangeTblRef);
-	((RangeTblRef *) joinexpr->larg)->rtindex = parse->mergeTargetRelation;
-	joinexpr->rarg = linitial(parse->jointree->fromlist);	/* original join */
+	joinexpr->larg = (Node *) makeFromExpr(list_make1(rtr), parse->jointree->quals);
+	joinexpr->rarg = linitial(parse->jointree->fromlist);	/* source rel */
 	joinexpr->usingClause = NIL;
 	joinexpr->join_using_alias = NULL;
-	/* The quals are removed from the jointree and into this specific join */
-	joinexpr->quals = parse->jointree->quals;
+	joinexpr->quals = parse->mergeJoinCondition;
 	joinexpr->alias = NULL;
 	joinexpr->rtindex = joinrti;
 
@@ -233,6 +251,15 @@ transform_MERGE_to_join(Query *parse)
 			add_nulling_relids((Node *) parse->targetList,
 							   bms_make_singleton(parse->mergeTargetRelation),
 							   bms_make_singleton(joinrti));
+
+	/*
+	 * If there are any WHEN NOT MATCHED BY SOURCE actions, the executor will
+	 * use the join condition to distinguish between MATCHED and NOT MATCHED
+	 * BY SOURCE cases.  Otherwise, it's no longer needed, and we set it to
+	 * NULL, saving cycles during planning and execution.
+	 */
+	if (!have_action[MERGE_WHEN_NOT_MATCHED_BY_SOURCE])
+		parse->mergeJoinCondition = NULL;
 }
 
 /*
@@ -2173,6 +2200,8 @@ perform_pullup_replace_vars(PlannerInfo
 				pullup_replace_vars((Node *) action->targetList, rvcontext);
 		}
 	}
+	parse->mergeJoinCondition = pullup_replace_vars(parse->mergeJoinCondition,
+													rvcontext);
 	replace_vars_in_jointree((Node *) parse->jointree, rvcontext);
 	Assert(parse->setOperations == NULL);
 	parse->havingQual = pullup_replace_vars(parse->havingQual, rvcontext);
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
new file mode 100644
index 7698bfa..931b9c0
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -134,6 +134,7 @@ preprocess_targetlist(PlannerInfo *root)
 	if (command_type == CMD_MERGE)
 	{
 		ListCell   *l;
+		List	   *vars;
 
 		/*
 		 * For MERGE, handle targetlist of each MergeAction separately. Give
@@ -144,7 +145,6 @@ preprocess_targetlist(PlannerInfo *root)
 		foreach(l, parse->mergeActionList)
 		{
 			MergeAction *action = (MergeAction *) lfirst(l);
-			List	   *vars;
 			ListCell   *l2;
 
 			if (action->commandType == CMD_INSERT)
@@ -182,6 +182,30 @@ preprocess_targetlist(PlannerInfo *root)
 			}
 			list_free(vars);
 		}
+
+		/*
+		 * Add resjunk entries for any Vars and PlaceHolderVars used in the
+		 * join condition that belong to relations other than the target.  We
+		 * don't expect to see any aggregates or window functions here.
+		 */
+		vars = pull_var_clause(parse->mergeJoinCondition,
+							   PVC_INCLUDE_PLACEHOLDERS);
+		foreach(l, vars)
+		{
+			Var		   *var = (Var *) lfirst(l);
+			TargetEntry *tle;
+
+			if (IsA(var, Var) && var->varno == result_relation)
+				continue;		/* don't need it */
+
+			if (tlist_member((Expr *) var, tlist))
+				continue;		/* already got it */
+
+			tle = makeTargetEntry((Expr *) var,
+								  list_length(tlist) + 1,
+								  NULL, true);
+			tlist = lappend(tlist, tle);
+		}
 	}
 
 	/*
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
new file mode 100644
index 0a7e5c2..49f4c97
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -3714,6 +3714,7 @@ create_lockrows_path(PlannerInfo *root,
  * 'onconflict' is the ON CONFLICT clause, or NULL
  * 'epqParam' is the ID of Param for EvalPlanQual re-eval
  * 'mergeActionLists' is a list of lists of MERGE actions (one per rel)
+ * 'mergeJoinConditions' is a list of join conditions for MERGE (one per rel)
  */
 ModifyTablePath *
 create_modifytable_path(PlannerInfo *root, RelOptInfo *rel,
@@ -3725,7 +3726,8 @@ create_modifytable_path(PlannerInfo *roo
 						List *updateColnosLists,
 						List *withCheckOptionLists, List *returningLists,
 						List *rowMarks, OnConflictExpr *onconflict,
-						List *mergeActionLists, int epqParam)
+						List *mergeActionLists, List *mergeJoinConditions,
+						int epqParam)
 {
 	ModifyTablePath *pathnode = makeNode(ModifyTablePath);
 
@@ -3793,6 +3795,7 @@ create_modifytable_path(PlannerInfo *roo
 	pathnode->onconflict = onconflict;
 	pathnode->epqParam = epqParam;
 	pathnode->mergeActionLists = mergeActionLists;
+	pathnode->mergeJoinConditions = mergeJoinConditions;
 
 	return pathnode;
 }
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
new file mode 100644
index c247eef..bc9a793
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -275,6 +275,7 @@ static Node *makeRecursiveViewSelect(cha
 	struct SelectLimit *selectlimit;
 	SetQuantifier setquantifier;
 	struct GroupClause *groupclause;
+	MergeMatchKind mergematch;
 	MergeWhenClause *mergewhen;
 	struct KeyActions *keyactions;
 	struct KeyAction *keyaction;
@@ -516,6 +517,7 @@ static Node *makeRecursiveViewSelect(cha
 %type <onconflict> opt_on_conflict
 %type <mergewhen>	merge_insert merge_update merge_delete
 
+%type <mergematch> merge_when_tgt_matched merge_when_tgt_not_matched
 %type <node>	merge_when_clause opt_merge_when_condition
 %type <list>	merge_when_list
 
@@ -769,11 +771,11 @@ static Node *makeRecursiveViewSelect(cha
 	SAVEPOINT SCALAR SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT
 	SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
-	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
+	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SOURCE SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRING_P STRIP_P
 	SUBSCRIPTION SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
 
-	TABLE TABLES TABLESAMPLE TABLESPACE TEMP TEMPLATE TEMPORARY TEXT_P THEN
+	TABLE TABLES TABLESAMPLE TABLESPACE TARGET TEMP TEMPLATE TEMPORARY TEXT_P THEN
 	TIES TIME TIMESTAMP TO TRAILING TRANSACTION TRANSFORM
 	TREAT TRIGGER TRIM TRUE_P
 	TRUNCATE TRUSTED TYPE_P TYPES_P
@@ -12403,50 +12405,66 @@ merge_when_list:
 			| merge_when_list merge_when_clause		{ $$ = lappend($1,$2); }
 		;
 
+/*
+ * A WHEN clause may be WHEN MATCHED, WHEN NOT MATCHED BY SOURCE, or WHEN NOT
+ * MATCHED [BY TARGET]. The first two cases match target tuples, and support
+ * UPDATE/DELETE/DO NOTHING actions. The third case does not match target
+ * tuples, and only supports INSERT/DO NOTHING actions.
+ */
 merge_when_clause:
-			WHEN MATCHED opt_merge_when_condition THEN merge_update
+			merge_when_tgt_matched opt_merge_when_condition THEN merge_update
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN merge_delete
+			| merge_when_tgt_matched opt_merge_when_condition THEN merge_delete
 				{
-					$5->matched = true;
-					$5->condition = $3;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $5;
+					$$ = (Node *) $4;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN merge_insert
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN merge_insert
 				{
-					$6->matched = false;
-					$6->condition = $4;
+					$4->matchKind = $1;
+					$4->condition = $2;
 
-					$$ = (Node *) $6;
+					$$ = (Node *) $4;
 				}
-			| WHEN MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = true;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $3;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
-			| WHEN NOT MATCHED opt_merge_when_condition THEN DO NOTHING
+			| merge_when_tgt_not_matched opt_merge_when_condition THEN DO NOTHING
 				{
 					MergeWhenClause *m = makeNode(MergeWhenClause);
 
-					m->matched = false;
+					m->matchKind = $1;
 					m->commandType = CMD_NOTHING;
-					m->condition = $4;
+					m->condition = $2;
 
 					$$ = (Node *) m;
 				}
 		;
 
+merge_when_tgt_matched:
+			WHEN MATCHED					{ $$ = MERGE_WHEN_MATCHED; }
+			| WHEN NOT MATCHED BY SOURCE	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_SOURCE; }
+		;
+
+merge_when_tgt_not_matched:
+			WHEN NOT MATCHED				{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+			| WHEN NOT MATCHED BY TARGET	{ $$ = MERGE_WHEN_NOT_MATCHED_BY_TARGET; }
+		;
+
 opt_merge_when_condition:
 			AND a_expr				{ $$ = $2; }
 			|						{ $$ = NULL; }
@@ -17554,6 +17572,7 @@ unreserved_keyword:
 			| SIMPLE
 			| SKIP
 			| SNAPSHOT
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -17573,6 +17592,7 @@ unreserved_keyword:
 			| SYSTEM_P
 			| TABLES
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
@@ -18183,6 +18203,7 @@ bare_label_keyword:
 			| SMALLINT
 			| SNAPSHOT
 			| SOME
+			| SOURCE
 			| SQL_P
 			| STABLE
 			| STANDALONE_P
@@ -18207,6 +18228,7 @@ bare_label_keyword:
 			| TABLES
 			| TABLESAMPLE
 			| TABLESPACE
+			| TARGET
 			| TEMP
 			| TEMPLATE
 			| TEMPORARY
diff --git a/src/backend/parser/parse_merge.c b/src/backend/parser/parse_merge.c
new file mode 100644
index 04ed5e6..bce11d5
--- a/src/backend/parser/parse_merge.c
+++ b/src/backend/parser/parse_merge.c
@@ -40,9 +40,9 @@ static void setNamespaceVisibilityForRTE
  * Make appropriate changes to the namespace visibility while transforming
  * individual action's quals and targetlist expressions. In particular, for
  * INSERT actions we must only see the source relation (since INSERT action is
- * invoked for NOT MATCHED tuples and hence there is no target tuple to deal
- * with). On the other hand, UPDATE and DELETE actions can see both source and
- * target relations.
+ * invoked for NOT MATCHED [BY TARGET] tuples and hence there is no target
+ * tuple to deal with). On the other hand, UPDATE and DELETE actions can see
+ * both source and target relations, unless invoked for NOT MATCHED BY SOURCE.
  *
  * Also, since the internal join node can hide the source and target
  * relations, we must explicitly make the respective relation as visible so
@@ -58,7 +58,7 @@ setNamespaceForMergeWhen(ParseState *pst
 	targetRelRTE = rt_fetch(targetRTI, pstate->p_rtable);
 	sourceRelRTE = rt_fetch(sourceRTI, pstate->p_rtable);
 
-	if (mergeWhenClause->matched)
+	if (mergeWhenClause->matchKind == MERGE_WHEN_MATCHED)
 	{
 		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
 			   mergeWhenClause->commandType == CMD_DELETE ||
@@ -70,11 +70,25 @@ setNamespaceForMergeWhen(ParseState *pst
 		setNamespaceVisibilityForRTE(pstate->p_namespace,
 									 sourceRelRTE, true, true);
 	}
-	else
+	else if (mergeWhenClause->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
 	{
 		/*
-		 * NOT MATCHED actions can't see target relation, but they can see
-		 * source relation.
+		 * NOT MATCHED BY SOURCE actions can see the target relation, but they
+		 * can't see the source relation.
+		 */
+		Assert(mergeWhenClause->commandType == CMD_UPDATE ||
+			   mergeWhenClause->commandType == CMD_DELETE ||
+			   mergeWhenClause->commandType == CMD_NOTHING);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 targetRelRTE, true, true);
+		setNamespaceVisibilityForRTE(pstate->p_namespace,
+									 sourceRelRTE, false, false);
+	}
+	else						/* MERGE_WHEN_NOT_MATCHED_BY_TARGET */
+	{
+		/*
+		 * NOT MATCHED [BY TARGET] actions can't see target relation, but they
+		 * can see source relation.
 		 */
 		Assert(mergeWhenClause->commandType == CMD_INSERT ||
 			   mergeWhenClause->commandType == CMD_NOTHING);
@@ -95,10 +109,9 @@ transformMergeStmt(ParseState *pstate, M
 	Query	   *qry = makeNode(Query);
 	ListCell   *l;
 	AclMode		targetPerms = ACL_NO_RIGHTS;
-	bool		is_terminal[2];
+	bool		is_terminal[3];
 	Index		sourceRTI;
 	List	   *mergeActionList;
-	Node	   *joinExpr;
 	ParseNamespaceItem *nsitem;
 
 	/* There can't be any outer WITH to worry about */
@@ -122,12 +135,12 @@ transformMergeStmt(ParseState *pstate, M
 	/*
 	 * Check WHEN clauses for permissions and sanity
 	 */
-	is_terminal[0] = false;
-	is_terminal[1] = false;
+	is_terminal[MERGE_WHEN_MATCHED] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_SOURCE] = false;
+	is_terminal[MERGE_WHEN_NOT_MATCHED_BY_TARGET] = false;
 	foreach(l, stmt->mergeWhenClauses)
 	{
 		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
-		int			when_type = (mergeWhenClause->matched ? 0 : 1);
 
 		/*
 		 * Collect permissions to check, according to action types. We require
@@ -157,12 +170,12 @@ transformMergeStmt(ParseState *pstate, M
 		/*
 		 * Check for unreachable WHEN clauses
 		 */
-		if (is_terminal[when_type])
+		if (is_terminal[mergeWhenClause->matchKind])
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
 					 errmsg("unreachable WHEN clause specified after unconditional WHEN clause")));
 		if (mergeWhenClause->condition == NULL)
-			is_terminal[when_type] = true;
+			is_terminal[mergeWhenClause->matchKind] = true;
 	}
 
 	/*
@@ -223,16 +236,15 @@ transformMergeStmt(ParseState *pstate, M
 	 * side, so add that to the namespace.
 	 */
 	addNSItemToQuery(pstate, pstate->p_target_nsitem, false, true, true);
-	joinExpr = transformExpr(pstate, stmt->joinCondition,
-							 EXPR_KIND_JOIN_ON);
+	qry->mergeJoinCondition = transformExpr(pstate, stmt->joinCondition,
+											EXPR_KIND_JOIN_ON);
 
 	/*
 	 * Create the temporary query's jointree using the joinlist we built using
-	 * just the source relation; the target relation is not included.  The
-	 * quals we use are the join conditions to the merge target.  The join
+	 * just the source relation; the target relation is not included. The join
 	 * will be constructed fully by transform_MERGE_to_join.
 	 */
-	qry->jointree = makeFromExpr(pstate->p_joinlist, joinExpr);
+	qry->jointree = makeFromExpr(pstate->p_joinlist, NULL);
 
 	/* Transform the RETURNING list, if any */
 	qry->returningList = transformReturningList(pstate, stmt->returningList,
@@ -260,11 +272,7 @@ transformMergeStmt(ParseState *pstate, M
 
 		action = makeNode(MergeAction);
 		action->commandType = mergeWhenClause->commandType;
-		action->matched = mergeWhenClause->matched;
-
-		/* Use an outer join if any INSERT actions exist in the command. */
-		if (action->commandType == CMD_INSERT)
-			qry->mergeUseOuterJoin = true;
+		action->matchKind = mergeWhenClause->matchKind;
 
 		/*
 		 * Set namespace for the specific action. This must be done before
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
new file mode 100644
index 4a7402e..0832d45
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -7109,6 +7109,7 @@ get_merge_query_def(Query *query, depars
 	StringInfo	buf = context->buf;
 	RangeTblEntry *rte;
 	ListCell   *lc;
+	bool		haveNotMatchedBySource;
 
 	/* Insert the WITH clause if given */
 	get_with_clause(query, context);
@@ -7134,7 +7135,26 @@ get_merge_query_def(Query *query, depars
 	get_from_clause(query, " USING ", context);
 	appendContextKeyword(context, " ON ",
 						 -PRETTYINDENT_STD, PRETTYINDENT_STD, 2);
-	get_rule_expr(query->jointree->quals, context, false);
+	get_rule_expr(query->mergeJoinCondition, context, false);
+
+	/*
+	 * Test for any NOT MATCHED BY SOURCE actions.  If there are none, then
+	 * any NOT MATCHED BY TARGET actions are output as "WHEN NOT MATCHED", per
+	 * SQL standard.  Otherwise, we have a non-SQL-standard query, so output
+	 * "BY SOURCE" / "BY TARGET" qualifiers for all NOT MATCHED actions, to be
+	 * more explicit.
+	 */
+	haveNotMatchedBySource = false;
+	foreach(lc, query->mergeActionList)
+	{
+		MergeAction *action = lfirst_node(MergeAction, lc);
+
+		if (action->matchKind == MERGE_WHEN_NOT_MATCHED_BY_SOURCE)
+		{
+			haveNotMatchedBySource = true;
+			break;
+		}
+	}
 
 	/* Print each merge action */
 	foreach(lc, query->mergeActionList)
@@ -7143,7 +7163,24 @@ get_merge_query_def(Query *query, depars
 
 		appendContextKeyword(context, " WHEN ",
 							 -PRETTYINDENT_STD, PRETTYINDENT_STD, 2);
-		appendStringInfo(buf, "%sMATCHED", action->matched ? "" : "NOT ");
+		switch (action->matchKind)
+		{
+			case MERGE_WHEN_MATCHED:
+				appendStringInfo(buf, "MATCHED");
+				break;
+			case MERGE_WHEN_NOT_MATCHED_BY_SOURCE:
+				appendStringInfo(buf, "NOT MATCHED BY SOURCE");
+				break;
+			case MERGE_WHEN_NOT_MATCHED_BY_TARGET:
+				if (haveNotMatchedBySource)
+					appendStringInfo(buf, "NOT MATCHED BY TARGET");
+				else
+					appendStringInfo(buf, "NOT MATCHED");
+				break;
+			default:
+				elog(ERROR, "unrecognized matchKind: %d",
+					 (int) action->matchKind);
+		}
 
 		if (action->qual)
 		{
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
new file mode 100644
index 56d723d..c6977a6
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -4335,17 +4335,35 @@ psql_completion(const char *text, int st
 			 TailMatches("USING", MatchAny, MatchAny, "ON", MatchAny, MatchAny, MatchAny, "WHEN"))
 		COMPLETE_WITH("MATCHED", "NOT MATCHED");
 
-	/* Complete ... WHEN [NOT] MATCHED with THEN/AND */
+	/*
+	 * Complete ... WHEN MATCHED and WHEN NOT MATCHED BY SOURCE|TARGET with
+	 * THEN/AND
+	 */
 	else if (TailMatches("WHEN", "MATCHED") ||
-			 TailMatches("WHEN", "NOT", "MATCHED"))
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE|TARGET"))
 		COMPLETE_WITH("THEN", "AND");
 
-	/* Complete ... WHEN MATCHED THEN with UPDATE SET/DELETE/DO NOTHING */
-	else if (TailMatches("WHEN", "MATCHED", "THEN"))
+	/* Complete ... WHEN NOT MATCHED with BY/THEN/AND */
+	else if (TailMatches("WHEN", "NOT", "MATCHED"))
+		COMPLETE_WITH("BY", "THEN", "AND");
+
+	/* Complete ... WHEN NOT MATCHED BY with SOURCE/TARGET */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "BY"))
+		COMPLETE_WITH("SOURCE", "TARGET");
+
+	/*
+	 * Complete ... WHEN MATCHED THEN and WHEN NOT MATCHED BY SOURCE THEN with
+	 * UPDATE SET/DELETE/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "SOURCE", "THEN"))
 		COMPLETE_WITH("UPDATE SET", "DELETE", "DO NOTHING");
 
-	/* Complete ... WHEN NOT MATCHED THEN with INSERT/DO NOTHING */
-	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN"))
+	/*
+	 * Complete ... WHEN NOT MATCHED [BY TARGET] THEN with INSERT/DO NOTHING
+	 */
+	else if (TailMatches("WHEN", "NOT", "MATCHED", "THEN") ||
+			 TailMatches("WHEN", "NOT", "MATCHED", "BY", "TARGET", "THEN"))
 		COMPLETE_WITH("INSERT", "DO NOTHING");
 
 /* NOTIFY --- can be inside EXPLAIN, RULE, etc */
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
new file mode 100644
index 1774c56..88cc936
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -544,9 +544,11 @@ typedef struct ResultRelInfo
 	/* ON CONFLICT evaluation state */
 	OnConflictSetState *ri_onConflict;
 
-	/* for MERGE, lists of MergeActionState */
-	List	   *ri_matchedMergeAction;
-	List	   *ri_notMatchedMergeAction;
+	/* for MERGE, lists of MergeActionState (one per MergeMatchKind) */
+	List	   *ri_MergeActions[3];
+
+	/* for MERGE, join condition-checking expr state */
+	ExprState  *ri_MergeJoinCondition;
 
 	/* partition check expression state (NULL if not set up yet) */
 	ExprState  *ri_PartitionCheckExpr;
@@ -1401,6 +1403,13 @@ typedef struct ModifyTableState
 	/* For MERGE, the action currently being executed */
 	MergeActionState *mt_merge_action;
 
+	/*
+	 * For MERGE, if there is a pending NOT MATCHED [BY TARGET] action to be
+	 * performed, this will be the last tuple read from the subplan; otherwise
+	 * it will be NULL --- see the comments in ExecMerge().
+	 */
+	TupleTableSlot *mt_merge_pending_not_matched;
+
 	/* tuple counters for MERGE */
 	double		mt_merge_inserted;
 	double		mt_merge_updated;
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
new file mode 100644
index 9b709f0..8f81826
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -176,8 +176,6 @@ typedef struct Query
 								 * also USING clause for MERGE */
 
 	List	   *mergeActionList;	/* list of actions for MERGE (only) */
-	/* whether to use outer join */
-	bool		mergeUseOuterJoin pg_node_attr(query_jumble_ignore);
 
 	/*
 	 * rtable index of target relation for MERGE to pull data. Initially, this
@@ -187,6 +185,9 @@ typedef struct Query
 	 */
 	int			mergeTargetRelation pg_node_attr(query_jumble_ignore);
 
+	/* join condition between source and target for MERGE */
+	Node	   *mergeJoinCondition;
+
 	List	   *targetList;		/* target list (of TargetEntry) */
 
 	/* OVERRIDING clause */
@@ -1677,7 +1678,7 @@ typedef struct CommonTableExpr
 typedef struct MergeWhenClause
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	OverridingKind override;	/* OVERRIDING clause */
 	Node	   *condition;		/* WHEN conditions (raw parser) */
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
new file mode 100644
index 534692b..5ccfa5f
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -2367,6 +2367,8 @@ typedef struct ModifyTablePath
 	int			epqParam;		/* ID of Param for EvalPlanQual re-eval */
 	List	   *mergeActionLists;	/* per-target-table lists of actions for
 									 * MERGE */
+	List	   *mergeJoinConditions;	/* per-target-table join conditions
+										 * for MERGE */
 } ModifyTablePath;
 
 /*
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
new file mode 100644
index 7f3db51..e025679
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -251,6 +251,8 @@ typedef struct ModifyTable
 	List	   *exclRelTlist;	/* tlist of the EXCLUDED pseudo relation */
 	List	   *mergeActionLists;	/* per-target-table lists of actions for
 									 * MERGE */
+	List	   *mergeJoinConditions;	/* per-target-table join conditions
+										 * for MERGE */
 } ModifyTable;
 
 struct PartitionPruneInfo;		/* forward reference to struct below */
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
new file mode 100644
index 376f67e..aa727e7
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -1875,10 +1875,18 @@ typedef struct BooleanTest
  *
  * Transformed representation of a WHEN clause in a MERGE statement
  */
+
+typedef enum MergeMatchKind
+{
+	MERGE_WHEN_MATCHED,
+	MERGE_WHEN_NOT_MATCHED_BY_SOURCE,
+	MERGE_WHEN_NOT_MATCHED_BY_TARGET
+} MergeMatchKind;
+
 typedef struct MergeAction
 {
 	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
+	MergeMatchKind matchKind;	/* MATCHED/NOT MATCHED BY SOURCE/TARGET */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
 	/* OVERRIDING clause */
 	OverridingKind override pg_node_attr(query_jumble_ignore);
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
new file mode 100644
index 99c2f95..527ef0b
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -283,7 +283,8 @@ extern ModifyTablePath *create_modifytab
 												List *updateColnosLists,
 												List *withCheckOptionLists, List *returningLists,
 												List *rowMarks, OnConflictExpr *onconflict,
-												List *mergeActionLists, int epqParam);
+												List *mergeActionLists, List *mergeJoinConditions,
+												int epqParam);
 extern LimitPath *create_limit_path(PlannerInfo *root, RelOptInfo *rel,
 									Path *subpath,
 									Node *limitOffset, Node *limitCount,
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
new file mode 100644
index 3941ef1..cf7836d
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -413,6 +413,7 @@ PG_KEYWORD("skip", SKIP, UNRESERVED_KEYW
 PG_KEYWORD("smallint", SMALLINT, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("snapshot", SNAPSHOT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("some", SOME, RESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("source", SOURCE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("sql", SQL_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("stable", STABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("standalone", STANDALONE_P, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -437,6 +438,7 @@ PG_KEYWORD("table", TABLE, RESERVED_KEYW
 PG_KEYWORD("tables", TABLES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablesample", TABLESAMPLE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("tablespace", TABLESPACE, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("target", TARGET, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temp", TEMP, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("template", TEMPLATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("temporary", TEMPORARY, UNRESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/test/isolation/expected/merge-update.out b/src/test/isolation/expected/merge-update.out
new file mode 100644
index f5f7e3b..3063c0c
--- a/src/test/isolation/expected/merge-update.out
+++ b/src/test/isolation/expected/merge-update.out
@@ -37,13 +37,22 @@ step merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a'
+  RETURNING merge_action(), t.*;
+
+merge_action|key|val                                                   
+------------+---+------------------------------------------------------
+UPDATE      |  3|setup1 updated by merge1 source not matched by merge2a
+INSERT      |  1|merge2a                                               
+(2 rows)
 
 step select2: SELECT * FROM target;
-key|val                     
----+------------------------
-  2|setup1 updated by merge1
-  1|merge2a                 
+key|val                                                   
+---+------------------------------------------------------
+  3|setup1 updated by merge1 source not matched by merge2a
+  1|merge2a                                               
 (2 rows)
 
 step c2: COMMIT;
@@ -86,15 +95,24 @@ step merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a'
+  RETURNING merge_action(), t.*;
  <waiting ...>
 step c1: COMMIT;
 step merge2a: <... completed>
+merge_action|key|val                                                   
+------------+---+------------------------------------------------------
+UPDATE      |  3|setup1 updated by merge1 source not matched by merge2a
+INSERT      |  1|merge2a                                               
+(2 rows)
+
 step select2: SELECT * FROM target;
-key|val                     
----+------------------------
-  2|setup1 updated by merge1
-  1|merge2a                 
+key|val                                                   
+---+------------------------------------------------------
+  3|setup1 updated by merge1 source not matched by merge2a
+  1|merge2a                                               
 (2 rows)
 
 step c2: COMMIT;
@@ -116,10 +134,18 @@ step merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a'
+  RETURNING merge_action(), t.*;
  <waiting ...>
 step a1: ABORT;
 step merge2a: <... completed>
+merge_action|key|val                      
+------------+---+-------------------------
+UPDATE      |  2|setup1 updated by merge2a
+(1 row)
+
 step select2: SELECT * FROM target;
 key|val                      
 ---+-------------------------
@@ -205,15 +231,24 @@ step pa_merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a'
+  RETURNING merge_action(), t.*;
  <waiting ...>
 step c1: COMMIT;
 step pa_merge2a: <... completed>
+merge_action|key|val                                               
+------------+---+--------------------------------------------------
+UPDATE      |  2|initial updated by pa_merge1 updated by pa_merge2a
+UPDATE      |  3|initial source not matched by pa_merge2a          
+(2 rows)
+
 step pa_select2: SELECT * FROM pa_target;
 key|val                                               
 ---+--------------------------------------------------
-  2|initial                                           
   2|initial updated by pa_merge1 updated by pa_merge2a
+  3|initial source not matched by pa_merge2a          
 (2 rows)
 
 step c2: COMMIT;
@@ -235,7 +270,10 @@ step pa_merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a'
+  RETURNING merge_action(), t.*;
  <waiting ...>
 step c1: COMMIT;
 step pa_merge2a: <... completed>
@@ -262,14 +300,24 @@ step pa_merge2a:
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a'
+  RETURNING merge_action(), t.*;
+
+merge_action|key|val                                                          
+------------+---+-------------------------------------------------------------
+UPDATE      |  3|initial source not matched by pa_merge2a                     
+UPDATE      |  3|initial updated by pa_merge2 source not matched by pa_merge2a
+INSERT      |  1|pa_merge2a                                                   
+(3 rows)
 
 step pa_select2: SELECT * FROM pa_target;
-key|val                         
----+----------------------------
-  1|pa_merge2a                  
-  2|initial                     
-  2|initial updated by pa_merge2
+key|val                                                          
+---+-------------------------------------------------------------
+  1|pa_merge2a                                                   
+  3|initial source not matched by pa_merge2a                     
+  3|initial updated by pa_merge2 source not matched by pa_merge2a
 (3 rows)
 
 step c2: COMMIT;
diff --git a/src/test/isolation/specs/merge-update.spec b/src/test/isolation/specs/merge-update.spec
new file mode 100644
index 3ccd466..a33dcdb
--- a/src/test/isolation/specs/merge-update.spec
+++ b/src/test/isolation/specs/merge-update.spec
@@ -92,7 +92,10 @@ step "merge2a"
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by merge2a'
+  RETURNING merge_action(), t.*;
 }
 step "merge2b"
 {
@@ -122,7 +125,10 @@ step "pa_merge2a"
   WHEN NOT MATCHED THEN
 	INSERT VALUES (s.key, s.val)
   WHEN MATCHED THEN
-	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val
+  WHEN NOT MATCHED BY SOURCE THEN
+	UPDATE set key = t.key + 1, val = t.val || ' source not matched by pa_merge2a'
+  RETURNING merge_action(), t.*;
 }
 # MERGE proceeds only if 'val' unchanged
 step "pa_merge2b_when"
diff --git a/src/test/regress/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index cec7f11..eddc1f4
--- a/src/test/regress/expected/merge.out
+++ b/src/test/regress/expected/merge.out
@@ -72,6 +72,15 @@ WHEN MATCHED THEN
 ERROR:  syntax error at or near "INSERT"
 LINE 5:  INSERT DEFAULT VALUES;
          ^
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
+ERROR:  syntax error at or near "INSERT"
+LINE 5:  INSERT DEFAULT VALUES;
+         ^
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -108,6 +117,15 @@ WHEN NOT MATCHED THEN
 ERROR:  syntax error at or near "UPDATE"
 LINE 5:  UPDATE SET balance = 0;
          ^
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
+ERROR:  syntax error at or near "UPDATE"
+LINE 5:  UPDATE SET balance = 0;
+         ^
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -270,6 +288,31 @@ SELECT * FROM target ORDER BY tid;
 (4 rows)
 
 ROLLBACK;
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta)
+RETURNING merge_action(), t.*;
+ merge_action | tid | balance 
+--------------+-----+---------
+ DELETE       |   1 |      10
+ DELETE       |   2 |      20
+ DELETE       |   3 |      30
+ INSERT       |   4 |      40
+(4 rows)
+
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   4 |      40
+(1 row)
+
+ROLLBACK;
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -737,6 +780,19 @@ SELECT * FROM wq_target;
    1 |      -1
 (1 row)
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+ERROR:  invalid reference to FROM-clause entry for table "s"
+LINE 3: WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+                                       ^
+DETAIL:  There is an entry for table "s", but it cannot be referenced from this part of the query.
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
  balance | sid 
@@ -922,6 +978,54 @@ SELECT * FROM target ORDER BY tid;
 (3 rows)
 
 ROLLBACK;
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+RETURNING merge_action(), t.*;
+NOTICE:  BEFORE INSERT STATEMENT trigger
+NOTICE:  BEFORE UPDATE STATEMENT trigger
+NOTICE:  BEFORE DELETE STATEMENT trigger
+NOTICE:  BEFORE UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  BEFORE INSERT ROW trigger row: (4,40)
+NOTICE:  BEFORE DELETE ROW trigger row: (2,20)
+NOTICE:  BEFORE UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER UPDATE ROW trigger row: (3,30) -> (3,10)
+NOTICE:  AFTER INSERT ROW trigger row: (4,40)
+NOTICE:  AFTER DELETE ROW trigger row: (2,20)
+NOTICE:  AFTER UPDATE ROW trigger row: (1,10) -> (1,0)
+NOTICE:  AFTER DELETE STATEMENT trigger
+NOTICE:  AFTER UPDATE STATEMENT trigger
+NOTICE:  AFTER INSERT STATEMENT trigger
+ merge_action | tid | balance 
+--------------+-----+---------
+ UPDATE       |   3 |      10
+ INSERT       |   4 |      40
+ DELETE       |   2 |      20
+ UPDATE       |   1 |       0
+(4 rows)
+
+SELECT * FROM target ORDER BY tid;
+ tid | balance 
+-----+---------
+   1 |       0
+   3 |      10
+   4 |      40
+(3 rows)
+
+ROLLBACK;
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -1636,6 +1740,50 @@ WHEN NOT MATCHED AND s.a < 20 THEN
                ->  Seq Scan on ex_mtarget t (actual rows=49 loops=1)
 (12 rows)
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=54
+   ->  Merge Left Join (actual rows=54 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+                            explain_merge                             
+----------------------------------------------------------------------
+ Merge on ex_mtarget t (actual rows=0 loops=1)
+   Tuples: skipped=100
+   ->  Merge Full Join (actual rows=100 loops=1)
+         Merge Cond: (t.a = s.a)
+         ->  Sort (actual rows=54 loops=1)
+               Sort Key: t.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_mtarget t (actual rows=54 loops=1)
+         ->  Sort (actual rows=100 loops=1)
+               Sort Key: s.a
+               Sort Method: quicksort  Memory: xxx
+               ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
+(12 rows)
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
@@ -1765,7 +1913,7 @@ CREATE TABLE pa_source (sid integer, del
 -- insert many rows to the source table
 INSERT INTO pa_source SELECT id, id * 10  FROM generate_series(1,14) AS id;
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 -- try simple MERGE
 BEGIN;
 MERGE INTO pa_target t
@@ -1774,10 +1922,12 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
    3 |     330 | initial updated by merge
@@ -1792,7 +1942,8 @@ SELECT * FROM pa_target ORDER BY tid;
   12 |     120 | inserted by merge
   13 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+  15 |    1500 | initial not matched by source
+(15 rows)
 
 ROLLBACK;
 -- same with a constant qual
@@ -1803,31 +1954,34 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
+   3 |     300 | initial not matched by source
    3 |      30 | inserted by merge
-   3 |     300 | initial
    4 |      40 | inserted by merge
-   5 |     500 | initial
+   5 |     500 | initial not matched by source
    5 |      50 | inserted by merge
    6 |      60 | inserted by merge
-   7 |     700 | initial
+   7 |     700 | initial not matched by source
    7 |      70 | inserted by merge
    8 |      80 | inserted by merge
+   9 |     900 | initial not matched by source
    9 |      90 | inserted by merge
-   9 |     900 | initial
   10 |     100 | inserted by merge
-  11 |    1100 | initial
+  11 |    1100 | initial not matched by source
   11 |     110 | inserted by merge
   12 |     120 | inserted by merge
-  13 |    1300 | initial
+  13 |    1300 | initial not matched by source
   13 |     130 | inserted by merge
   14 |     140 | inserted by merge
-(20 rows)
+  15 |    1500 | initial not matched by source
+(21 rows)
 
 ROLLBACK;
 -- try updating the partition key column
@@ -1842,7 +1996,9 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 IF FOUND THEN
   GET DIAGNOSTICS result := ROW_COUNT;
 END IF;
@@ -1852,27 +2008,28 @@ $$;
 SELECT merge_func();
  merge_func 
 ------------
-         14
+         15
 (1 row)
 
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
+   1 |    1500 | initial not matched by source
    2 |     110 | initial updated by merge
    2 |      20 | inserted by merge
-   4 |      40 | inserted by merge
    4 |     330 | initial updated by merge
+   4 |      40 | inserted by merge
    6 |     550 | initial updated by merge
    6 |      60 | inserted by merge
-   8 |      80 | inserted by merge
    8 |     770 | initial updated by merge
+   8 |      80 | inserted by merge
   10 |     990 | initial updated by merge
   10 |     100 | inserted by merge
   12 |    1210 | initial updated by merge
   12 |     120 | inserted by merge
   14 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+(15 rows)
 
 ROLLBACK;
 -- update partition key to partition not initially scanned
@@ -1898,7 +2055,8 @@ SELECT * FROM pa_target ORDER BY tid;
    9 |     900 | initial
   11 |    1100 | initial
   13 |    1300 | initial
-(7 rows)
+  15 |    1500 | initial
+(8 rows)
 
 ROLLBACK;
 DROP TABLE pa_target CASCADE;
@@ -1920,7 +2078,7 @@ ALTER TABLE pa_target ATTACH PARTITION p
 ALTER TABLE pa_target ATTACH PARTITION part3 FOR VALUES IN (3,8,9);
 ALTER TABLE pa_target ATTACH PARTITION part4 DEFAULT;
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 -- try simple MERGE
 BEGIN;
 DO $$
@@ -1933,15 +2091,17 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 14
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 15
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
    3 |     330 | initial updated by merge
@@ -1956,7 +2116,8 @@ SELECT * FROM pa_target ORDER BY tid;
   12 |     120 | inserted by merge
   13 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+  15 |    1500 | initial not matched by source
+(15 rows)
 
 ROLLBACK;
 -- same with a constant qual
@@ -1968,29 +2129,32 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     110 | initial updated by merge
    2 |      20 | inserted by merge
+   3 |     300 | initial not matched by source
    3 |      30 | inserted by merge
-   3 |     300 | initial
    4 |      40 | inserted by merge
    6 |      60 | inserted by merge
-   7 |     700 | initial
+   7 |     700 | initial not matched by source
    7 |      70 | inserted by merge
    8 |      80 | inserted by merge
-   9 |     900 | initial
+   9 |     900 | initial not matched by source
    9 |      90 | inserted by merge
   10 |     100 | inserted by merge
+  11 |    1100 | initial not matched by source
   11 |     110 | inserted by merge
-  11 |    1100 | initial
   12 |     120 | inserted by merge
-  13 |    1300 | initial
+  13 |    1300 | initial not matched by source
   13 |     130 | inserted by merge
   14 |     140 | inserted by merge
-(18 rows)
+  15 |    1500 | initial not matched by source
+(19 rows)
 
 ROLLBACK;
 -- try updating the partition key column
@@ -2005,30 +2169,33 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 14
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 15
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
+   1 |    1500 | initial not matched by source
    2 |     110 | initial updated by merge
    2 |      20 | inserted by merge
-   4 |      40 | inserted by merge
    4 |     330 | initial updated by merge
+   4 |      40 | inserted by merge
    6 |     550 | initial updated by merge
    6 |      60 | inserted by merge
-   8 |      80 | inserted by merge
    8 |     770 | initial updated by merge
+   8 |      80 | inserted by merge
   10 |     990 | initial updated by merge
   10 |     100 | inserted by merge
   12 |    1210 | initial updated by merge
   12 |     120 | inserted by merge
   14 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+(15 rows)
 
 ROLLBACK;
 -- as above, but blocked by BEFORE DELETE ROW trigger
@@ -2047,15 +2214,17 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 10
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 11
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    1 |     100 | initial
    2 |      20 | inserted by merge
    3 |     300 | initial
@@ -2070,7 +2239,8 @@ SELECT * FROM pa_target ORDER BY tid;
   12 |     120 | inserted by merge
   14 |    1430 | initial updated by merge
   14 |     140 | inserted by merge
-(14 rows)
+  15 |    1500 | initial not matched by source
+(15 rows)
 
 ROLLBACK;
 -- as above, but blocked by BEFORE INSERT ROW trigger
@@ -2089,19 +2259,22 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-NOTICE:  ROW_COUNT = 3
-SELECT * FROM pa_target ORDER BY tid;
- tid | balance |           val            
------+---------+--------------------------
+NOTICE:  ROW_COUNT = 4
+SELECT * FROM pa_target ORDER BY tid, val;
+ tid | balance |              val              
+-----+---------+-------------------------------
    6 |     550 | initial updated by merge
   12 |    1210 | initial updated by merge
   14 |    1430 | initial updated by merge
-(3 rows)
+  15 |    1500 | initial not matched by source
+(4 rows)
 
 ROLLBACK;
 -- test RLS enforcement
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
new file mode 100644
index 84e359f..35d4eb6
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -3726,7 +3726,39 @@ BEGIN ATOMIC
      t.data,
      t.filling;
 END
+CREATE FUNCTION merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+   USING rule_merge1 s
+   ON (s.a = t.id)
+WHEN NOT MATCHED
+   THEN INSERT (data, id)
+   VALUES (s.a, s.a)
+WHEN MATCHED
+   THEN UPDATE SET data = s.b
+WHEN NOT MATCHED BY SOURCE
+   THEN DELETE;
+END;
+\sf merge_sf_test2
+CREATE OR REPLACE FUNCTION public.merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+    USING rule_merge1 s
+    ON (s.a = t.id)
+    WHEN NOT MATCHED BY TARGET
+     THEN INSERT (data, id)
+      VALUES (s.a, s.a)
+    WHEN MATCHED
+     THEN UPDATE SET data = s.b
+    WHEN NOT MATCHED BY SOURCE
+     THEN DELETE;
+END
 DROP FUNCTION merge_sf_test;
+DROP FUNCTION merge_sf_test2;
 DROP TABLE sf_target;
 --
 -- Test enabling/disabling
diff --git a/src/test/regress/expected/updatable_views.out b/src/test/regress/expected/updatable_views.out
new file mode 100644
index 713bf84..1d1f568
--- a/src/test/regress/expected/updatable_views.out
+++ b/src/test/regress/expected/updatable_views.out
@@ -499,6 +499,32 @@ SELECT * FROM base_tbl ORDER BY a;
   5 | Unspecified
 (6 rows)
 
+MERGE INTO rw_view1 t
+  USING (VALUES (0, 'R0'), (1, 'R1'),
+                (2, 'R2'), (3, 'R3')) AS v(a,b) ON t.a = v.a
+  WHEN MATCHED AND t.a <= 1 THEN UPDATE SET b = v.b
+  WHEN MATCHED THEN DELETE
+  WHEN NOT MATCHED BY SOURCE THEN DELETE
+  WHEN NOT MATCHED AND a > 0 THEN INSERT (a) VALUES (v.a)
+  RETURNING merge_action(), v.*, t.*;
+ merge_action | a | b  | a |      b      
+--------------+---+----+---+-------------
+ UPDATE       | 1 | R1 | 1 | R1
+ DELETE       |   |    | 5 | Unspecified
+ DELETE       | 2 | R2 | 2 | Unspecified
+ INSERT       | 3 | R3 | 3 | Unspecified
+(4 rows)
+
+SELECT * FROM base_tbl ORDER BY a;
+ a  |      b      
+----+-------------
+ -2 | Row -2
+ -1 | Row -1
+  0 | Row 0
+  1 | R1
+  3 | Unspecified
+(5 rows)
+
 EXPLAIN (costs off) UPDATE rw_view1 SET a=6 WHERE a=5;
                     QUERY PLAN                    
 --------------------------------------------------
@@ -545,6 +571,23 @@ MERGE INTO rw_view1 t
 EXPLAIN (costs off)
 MERGE INTO rw_view1 t
   USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
+  WHEN NOT MATCHED BY SOURCE THEN DELETE;
+                            QUERY PLAN                             
+-------------------------------------------------------------------
+ Merge on base_tbl
+   ->  Hash Left Join
+         Hash Cond: (base_tbl.a = generate_series.generate_series)
+         ->  Bitmap Heap Scan on base_tbl
+               Recheck Cond: (a > 0)
+               ->  Bitmap Index Scan on base_tbl_pkey
+                     Index Cond: (a > 0)
+         ->  Hash
+               ->  Function Scan on generate_series
+(9 rows)
+
+EXPLAIN (costs off)
+MERGE INTO rw_view1 t
+  USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
   WHEN NOT MATCHED THEN INSERT (a) VALUES (s.a);
                             QUERY PLAN                             
 -------------------------------------------------------------------
@@ -656,6 +699,29 @@ SELECT * FROM rw_view2 ORDER BY aaa;
    5 | Unspecified
 (3 rows)
 
+MERGE INTO rw_view2 t
+  USING (VALUES (4, 'r4'), (5, 'r5'), (6, 'r6')) AS v(a,b) ON aaa = v.a
+  WHEN MATCHED AND aaa = 4 THEN DELETE
+  WHEN MATCHED THEN UPDATE SET bbb = v.b
+  WHEN NOT MATCHED THEN INSERT (aaa) VALUES (v.a)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET bbb = 'Not matched by source'
+  RETURNING merge_action(), v.*, t.*;
+ merge_action | a | b  | aaa |          bbb          
+--------------+---+----+-----+-----------------------
+ UPDATE       |   |    |   1 | Not matched by source
+ DELETE       | 4 | r4 |   4 | R4
+ UPDATE       | 5 | r5 |   5 | r5
+ INSERT       | 6 | r6 |   6 | Unspecified
+(4 rows)
+
+SELECT * FROM rw_view2 ORDER BY aaa;
+ aaa |          bbb          
+-----+-----------------------
+   1 | Not matched by source
+   5 | r5
+   6 | Unspecified
+(3 rows)
+
 EXPLAIN (costs off) UPDATE rw_view2 SET aaa=5 WHERE aaa=4;
                        QUERY PLAN                       
 --------------------------------------------------------
@@ -1106,6 +1172,30 @@ SELECT * FROM base_tbl ORDER BY a;
   3 | R3
 (5 rows)
 
+MERGE INTO rw_view2 t
+  USING (SELECT x, 'r'||x FROM generate_series(0,2) x) AS s(a,b) ON t.a = s.a
+  WHEN MATCHED THEN UPDATE SET b = s.b
+  WHEN NOT MATCHED AND s.a > 0 THEN INSERT VALUES (s.a, s.b)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET b = 'Not matched by source'
+  RETURNING merge_action(), s.*, t.*;
+ merge_action | a | b  | a |           b           
+--------------+---+----+---+-----------------------
+ UPDATE       | 2 | r2 | 2 | r2
+ UPDATE       |   |    | 3 | Not matched by source
+ INSERT       | 1 | r1 | 1 | r1
+(3 rows)
+
+SELECT * FROM base_tbl ORDER BY a;
+ a  |           b           
+----+-----------------------
+ -2 | Row -2
+ -1 | Row -1
+  0 | Row 0
+  1 | r1
+  2 | r2
+  3 | Not matched by source
+(6 rows)
+
 EXPLAIN (costs off) UPDATE rw_view2 SET a=3 WHERE a=2;
                         QUERY PLAN                        
 ----------------------------------------------------------
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index 875cf6f..3d5d854
--- a/src/test/regress/sql/merge.sql
+++ b/src/test/regress/sql/merge.sql
@@ -53,6 +53,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN MATCHED THEN
 	INSERT DEFAULT VALUES;
+-- NOT MATCHED BY SOURCE/INSERT error
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	INSERT DEFAULT VALUES;
 -- incorrectly specifying INTO target
 MERGE INTO target t
 USING source AS s
@@ -77,6 +83,12 @@ USING source AS s
 ON t.tid = s.sid
 WHEN NOT MATCHED THEN
 	UPDATE SET balance = 0;
+-- NOT MATCHED BY TARGET/UPDATE
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY TARGET THEN
+	UPDATE SET balance = 0;
 -- UPDATE tablename
 MERGE INTO target t
 USING source AS s
@@ -214,6 +226,19 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- DELETE/INSERT not matched by source/target
+BEGIN;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET THEN
+	INSERT VALUES (s.sid, s.delta)
+RETURNING merge_action(), t.*;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- index plans
 INSERT INTO target SELECT generate_series(1000,2500), 0;
 ALTER TABLE target ADD PRIMARY KEY (tid);
@@ -498,6 +523,17 @@ WHEN NOT MATCHED AND s.balance = 100 THE
 	INSERT (tid) VALUES (s.sid);
 SELECT * FROM wq_target;
 
+-- conditions in NOT MATCHED BY SOURCE clause can only refer to target columns
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND s.balance = 100 THEN
+	DELETE;
+
+MERGE INTO wq_target t
+USING wq_source s ON t.tid = s.sid
+WHEN NOT MATCHED BY SOURCE AND t.balance = 100 THEN
+    DELETE;
+
 -- conditions in MATCHED clause can refer to both source and target
 SELECT * FROM wq_source;
 MERGE INTO wq_target t
@@ -625,6 +661,26 @@ WHEN NOT MATCHED THEN
 SELECT * FROM target ORDER BY tid;
 ROLLBACK;
 
+-- UPSERT with UPDATE/DELETE when not matched by source
+BEGIN;
+DELETE FROM SOURCE WHERE sid = 2;
+MERGE INTO target t
+USING source AS s
+ON t.tid = s.sid
+WHEN MATCHED AND t.balance > s.delta THEN
+    UPDATE SET balance = t.balance - s.delta
+WHEN MATCHED THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED THEN
+    INSERT VALUES (s.sid, s.delta)
+WHEN NOT MATCHED BY SOURCE AND tid = 1 THEN
+	UPDATE SET balance = 0
+WHEN NOT MATCHED BY SOURCE THEN
+	DELETE
+RETURNING merge_action(), t.*;
+SELECT * FROM target ORDER BY tid;
+ROLLBACK;
+
 -- Test behavior of triggers that turn UPDATE/DELETE into no-ops
 create or replace function skip_merge_op() returns trigger
 language plpgsql as
@@ -1061,6 +1117,20 @@ WHEN MATCHED AND t.a >= 30 AND t.a <= 40
 WHEN NOT MATCHED AND s.a < 20 THEN
 	INSERT VALUES (a, b)');
 
+-- not matched by source
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE and t.a < 10 THEN
+	DELETE');
+
+-- not matched by source and target
+SELECT explain_merge('
+MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a
+WHEN NOT MATCHED BY SOURCE AND t.a < 10 THEN
+	DELETE
+WHEN NOT MATCHED BY TARGET AND s.a < 20 THEN
+	INSERT VALUES (a, b)');
+
 -- nothing
 SELECT explain_merge('
 MERGE INTO ex_mtarget t USING ex_msource s ON t.a = s.a AND t.a < -1000
@@ -1133,7 +1203,7 @@ CREATE TABLE pa_source (sid integer, del
 -- insert many rows to the source table
 INSERT INTO pa_source SELECT id, id * 10  FROM generate_series(1,14) AS id;
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 
 -- try simple MERGE
 BEGIN;
@@ -1143,8 +1213,10 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- same with a constant qual
@@ -1155,8 +1227,10 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- try updating the partition key column
@@ -1171,7 +1245,9 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 IF FOUND THEN
   GET DIAGNOSTICS result := ROW_COUNT;
 END IF;
@@ -1179,7 +1255,7 @@ RETURN result;
 END;
 $$;
 SELECT merge_func();
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- update partition key to partition not initially scanned
@@ -1216,7 +1292,7 @@ ALTER TABLE pa_target ATTACH PARTITION p
 ALTER TABLE pa_target ATTACH PARTITION part4 DEFAULT;
 
 -- insert a few rows in the target table (odd numbered tid)
-INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,14,2) AS id;
+INSERT INTO pa_target SELECT id, id * 100, 'initial' FROM generate_series(1,15,2) AS id;
 
 -- try simple MERGE
 BEGIN;
@@ -1230,12 +1306,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- same with a constant qual
@@ -1247,8 +1325,10 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
-SELECT * FROM pa_target ORDER BY tid;
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- try updating the partition key column
@@ -1263,12 +1343,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET tid = 1, val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- as above, but blocked by BEFORE DELETE ROW trigger
@@ -1287,12 +1369,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- as above, but blocked by BEFORE INSERT ROW trigger
@@ -1311,12 +1395,14 @@ MERGE INTO pa_target t
   WHEN MATCHED THEN
     UPDATE SET tid = tid + 1, balance = balance + delta, val = val || ' updated by merge'
   WHEN NOT MATCHED THEN
-    INSERT VALUES (sid, delta, 'inserted by merge');
+    INSERT VALUES (sid, delta, 'inserted by merge')
+  WHEN NOT MATCHED BY SOURCE THEN
+    UPDATE SET val = val || ' not matched by source';
 GET DIAGNOSTICS result := ROW_COUNT;
 RAISE NOTICE 'ROW_COUNT = %', result;
 END;
 $$;
-SELECT * FROM pa_target ORDER BY tid;
+SELECT * FROM pa_target ORDER BY tid, val;
 ROLLBACK;
 
 -- test RLS enforcement
diff --git a/src/test/regress/sql/rules.sql b/src/test/regress/sql/rules.sql
new file mode 100644
index 27340ba..4a5fa50
--- a/src/test/regress/sql/rules.sql
+++ b/src/test/regress/sql/rules.sql
@@ -1338,7 +1338,26 @@ END;
 
 \sf merge_sf_test
 
+CREATE FUNCTION merge_sf_test2()
+ RETURNS void
+ LANGUAGE sql
+BEGIN ATOMIC
+ MERGE INTO sf_target t
+   USING rule_merge1 s
+   ON (s.a = t.id)
+WHEN NOT MATCHED
+   THEN INSERT (data, id)
+   VALUES (s.a, s.a)
+WHEN MATCHED
+   THEN UPDATE SET data = s.b
+WHEN NOT MATCHED BY SOURCE
+   THEN DELETE;
+END;
+
+\sf merge_sf_test2
+
 DROP FUNCTION merge_sf_test;
+DROP FUNCTION merge_sf_test2;
 DROP TABLE sf_target;
 
 --
diff --git a/src/test/regress/sql/updatable_views.sql b/src/test/regress/sql/updatable_views.sql
new file mode 100644
index afdf331..e0ab923
--- a/src/test/regress/sql/updatable_views.sql
+++ b/src/test/regress/sql/updatable_views.sql
@@ -179,6 +179,16 @@ MERGE INTO rw_view1 t
   RETURNING merge_action(), v.*, t.*;
 SELECT * FROM base_tbl ORDER BY a;
 
+MERGE INTO rw_view1 t
+  USING (VALUES (0, 'R0'), (1, 'R1'),
+                (2, 'R2'), (3, 'R3')) AS v(a,b) ON t.a = v.a
+  WHEN MATCHED AND t.a <= 1 THEN UPDATE SET b = v.b
+  WHEN MATCHED THEN DELETE
+  WHEN NOT MATCHED BY SOURCE THEN DELETE
+  WHEN NOT MATCHED AND a > 0 THEN INSERT (a) VALUES (v.a)
+  RETURNING merge_action(), v.*, t.*;
+SELECT * FROM base_tbl ORDER BY a;
+
 EXPLAIN (costs off) UPDATE rw_view1 SET a=6 WHERE a=5;
 EXPLAIN (costs off) DELETE FROM rw_view1 WHERE a=5;
 
@@ -194,6 +204,11 @@ MERGE INTO rw_view1 t
 EXPLAIN (costs off)
 MERGE INTO rw_view1 t
   USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
+  WHEN NOT MATCHED BY SOURCE THEN DELETE;
+
+EXPLAIN (costs off)
+MERGE INTO rw_view1 t
+  USING (SELECT * FROM generate_series(1,5)) AS s(a) ON t.a = s.a
   WHEN NOT MATCHED THEN INSERT (a) VALUES (s.a);
 
 -- it's still updatable if we add a DO ALSO rule
@@ -251,6 +266,15 @@ MERGE INTO rw_view2 t
   RETURNING merge_action(), v.*, t.*;
 SELECT * FROM rw_view2 ORDER BY aaa;
 
+MERGE INTO rw_view2 t
+  USING (VALUES (4, 'r4'), (5, 'r5'), (6, 'r6')) AS v(a,b) ON aaa = v.a
+  WHEN MATCHED AND aaa = 4 THEN DELETE
+  WHEN MATCHED THEN UPDATE SET bbb = v.b
+  WHEN NOT MATCHED THEN INSERT (aaa) VALUES (v.a)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET bbb = 'Not matched by source'
+  RETURNING merge_action(), v.*, t.*;
+SELECT * FROM rw_view2 ORDER BY aaa;
+
 EXPLAIN (costs off) UPDATE rw_view2 SET aaa=5 WHERE aaa=4;
 EXPLAIN (costs off) DELETE FROM rw_view2 WHERE aaa=4;
 
@@ -464,6 +488,14 @@ MERGE INTO rw_view2 t
   RETURNING merge_action(), s.*, t.*;
 SELECT * FROM base_tbl ORDER BY a;
 
+MERGE INTO rw_view2 t
+  USING (SELECT x, 'r'||x FROM generate_series(0,2) x) AS s(a,b) ON t.a = s.a
+  WHEN MATCHED THEN UPDATE SET b = s.b
+  WHEN NOT MATCHED AND s.a > 0 THEN INSERT VALUES (s.a, s.b)
+  WHEN NOT MATCHED BY SOURCE THEN UPDATE SET b = 'Not matched by source'
+  RETURNING merge_action(), s.*, t.*;
+SELECT * FROM base_tbl ORDER BY a;
+
 EXPLAIN (costs off) UPDATE rw_view2 SET a=3 WHERE a=2;
 EXPLAIN (costs off) DELETE FROM rw_view2 WHERE a=2;
 
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
new file mode 100644
index 3b8cec5..2beabb8
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1588,6 +1588,7 @@ MergeAppendState
 MergeJoin
 MergeJoinClause
 MergeJoinState
+MergeMatchKind
 MergePath
 MergeScanSelCache
 MergeStmt