Add semi-join pushdown to postgres_fdw

From 1ac2a9e3611f716da688c04a4ec36888f62078ce Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <a.pyhalov@postgrespro.ru>
Date: Mon, 7 Nov 2022 10:23:32 +0300
Subject: [PATCH] postgres_fdw: add support for deparsing semi joins

We deparse semi-joins as EXISTS subqueries. So, deparsing
semi-join leads to generating addl_conds condition,
which is then added to the uppermost JOIN's WHERE clause.
---
 contrib/postgres_fdw/deparse.c                | 198 +++++++++---
 .../postgres_fdw/expected/postgres_fdw.out    | 297 ++++++++++++++++--
 contrib/postgres_fdw/postgres_fdw.c           |  78 ++++-
 contrib/postgres_fdw/postgres_fdw.h           |   3 +-
 contrib/postgres_fdw/sql/postgres_fdw.sql     | 119 ++++++-
 5 files changed, 613 insertions(+), 82 deletions(-)

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index 95247656504..45885442418 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -179,12 +179,13 @@ static void appendLimitClause(deparse_expr_cxt *context);
 static void appendConditions(List *exprs, deparse_expr_cxt *context);
 static void deparseFromExprForRel(StringInfo buf, PlannerInfo *root,
 								  RelOptInfo *foreignrel, bool use_alias,
-								  Index ignore_rel, List **ignore_conds,
+								  Index ignore_rel, List **ignore_conds, StringInfo addl_conds,
 								  List **params_list);
+static void appendWhereClause(List *exprs, StringInfo addl_conds, deparse_expr_cxt *context);
 static void deparseFromExpr(List *quals, deparse_expr_cxt *context);
 static void deparseRangeTblRef(StringInfo buf, PlannerInfo *root,
 							   RelOptInfo *foreignrel, bool make_subquery,
-							   Index ignore_rel, List **ignore_conds, List **params_list);
+							   Index ignore_rel, List **ignore_conds, StringInfo addl_conds, List **params_list);
 static void deparseAggref(Aggref *node, deparse_expr_cxt *context);
 static void appendGroupByClause(List *tlist, deparse_expr_cxt *context);
 static void appendOrderBySuffix(Oid sortop, Oid sortcoltype, bool nulls_first,
@@ -1370,23 +1371,20 @@ deparseFromExpr(List *quals, deparse_expr_cxt *context)
 {
 	StringInfo	buf = context->buf;
 	RelOptInfo *scanrel = context->scanrel;
+	StringInfoData addl_conds;
 
 	/* For upper relations, scanrel must be either a joinrel or a baserel */
 	Assert(!IS_UPPER_REL(context->foreignrel) ||
 		   IS_JOIN_REL(scanrel) || IS_SIMPLE_REL(scanrel));
 
+	initStringInfo(&addl_conds);
 	/* Construct FROM clause */
 	appendStringInfoString(buf, " FROM ");
 	deparseFromExprForRel(buf, context->root, scanrel,
 						  (bms_membership(scanrel->relids) == BMS_MULTIPLE),
-						  (Index) 0, NULL, context->params_list);
-
-	/* Construct WHERE clause */
-	if (quals != NIL)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(quals, context);
-	}
+						  (Index) 0, NULL, &addl_conds, context->params_list);
+	appendWhereClause(quals, &addl_conds, context);
+	pfree(addl_conds.data);
 }
 
 /*
@@ -1598,6 +1596,33 @@ appendConditions(List *exprs, deparse_expr_cxt *context)
 	reset_transmission_modes(nestlevel);
 }
 
+/*
+ * Append WHERE clause, containing conditions
+ * from exprs and addl_conds, to context->buf.
+ */
+static void
+appendWhereClause(List *exprs, StringInfo addl_conds, deparse_expr_cxt *context)
+{
+	StringInfo	buf = context->buf;
+	bool		need_and = false;
+
+	if (exprs != NIL || addl_conds->len > 0)
+		appendStringInfoString(buf, " WHERE ");
+
+	if (exprs != NIL)
+	{
+		appendConditions(exprs, context);
+		need_and = true;
+	}
+
+	if (addl_conds->len > 0)
+	{
+		if (need_and)
+			appendStringInfoString(buf, " AND ");
+		appendStringInfo(buf, "(%s)", addl_conds->data);
+	}
+}
+
 /* Output join name for given join type */
 const char *
 get_jointype_name(JoinType jointype)
@@ -1616,6 +1641,9 @@ get_jointype_name(JoinType jointype)
 		case JOIN_FULL:
 			return "FULL";
 
+		case JOIN_SEMI:
+			return "SEMI";
+
 		default:
 			/* Shouldn't come here, but protect from buggy code. */
 			elog(ERROR, "unsupported join type %d", jointype);
@@ -1715,7 +1743,7 @@ deparseSubqueryTargetList(deparse_expr_cxt *context)
  */
 static void
 deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
-					  bool use_alias, Index ignore_rel, List **ignore_conds,
+					  bool use_alias, Index ignore_rel, List **ignore_conds, StringInfo addl_conds,
 					  List **params_list)
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
@@ -1728,6 +1756,9 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		RelOptInfo *innerrel = fpinfo->innerrel;
 		bool		outerrel_is_target = false;
 		bool		innerrel_is_target = false;
+		StringInfoData addl_conds_i;
+		StringInfoData addl_conds_o;
+		bool		need_and;
 
 		if (ignore_rel > 0 && bms_is_member(ignore_rel, foreignrel->relids))
 		{
@@ -1761,10 +1792,11 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		/* Deparse outer relation if not the target relation. */
 		if (!outerrel_is_target)
 		{
+			initStringInfo(&addl_conds_o);
 			initStringInfo(&join_sql_o);
 			deparseRangeTblRef(&join_sql_o, root, outerrel,
 							   fpinfo->make_outerrel_subquery,
-							   ignore_rel, ignore_conds, params_list);
+							   ignore_rel, ignore_conds, &addl_conds_o, params_list);
 
 			/*
 			 * If inner relation is the target relation, skip deparsing it.
@@ -1780,6 +1812,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				Assert(fpinfo->jointype == JOIN_INNER);
 				Assert(fpinfo->joinclauses == NIL);
 				appendBinaryStringInfo(buf, join_sql_o.data, join_sql_o.len);
+				if (addl_conds_o.len > 0)
+				{
+					Assert(addl_conds->len == 0);
+					appendStringInfoString(addl_conds, addl_conds_o.data);
+				}
+				pfree(addl_conds_o.data);
 				return;
 			}
 		}
@@ -1787,10 +1825,33 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		/* Deparse inner relation if not the target relation. */
 		if (!innerrel_is_target)
 		{
+			initStringInfo(&addl_conds_i);
+
 			initStringInfo(&join_sql_i);
 			deparseRangeTblRef(&join_sql_i, root, innerrel,
 							   fpinfo->make_innerrel_subquery,
-							   ignore_rel, ignore_conds, params_list);
+							   ignore_rel, ignore_conds, &addl_conds_i, params_list);
+
+			if (fpinfo->jointype == JOIN_SEMI)
+			{
+				deparse_expr_cxt context;
+
+				appendStringInfo(addl_conds, "EXISTS (SELECT NULL FROM %s", join_sql_i.data);
+
+				context.buf = addl_conds;
+				context.foreignrel = foreignrel;
+				context.scanrel = foreignrel;
+				context.root = root;
+				context.params_list = params_list;
+
+				appendWhereClause(fpinfo->joinclauses, &addl_conds_i, &context);
+
+				if (addl_conds_i.len > 0)
+					resetStringInfo(&addl_conds_i);
+
+				/* Close parentheses for EXISTS subquery */
+				appendStringInfo(addl_conds, ")");
+			}
 
 			/*
 			 * If outer relation is the target relation, skip deparsing it.
@@ -1801,6 +1862,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				Assert(fpinfo->jointype == JOIN_INNER);
 				Assert(fpinfo->joinclauses == NIL);
 				appendBinaryStringInfo(buf, join_sql_i.data, join_sql_i.len);
+				if (addl_conds_i.len > 0)
+				{
+					Assert(addl_conds->len == 0);
+					appendStringInfoString(addl_conds, addl_conds_i.data);
+				}
+				pfree(addl_conds_i.data);
 				return;
 			}
 		}
@@ -1809,33 +1876,69 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		Assert(!outerrel_is_target && !innerrel_is_target);
 
 		/*
-		 * For a join relation FROM clause entry is deparsed as
-		 *
-		 * ((outer relation) <join type> (inner relation) ON (joinclauses))
+		 * For semijoin FROM clause is deparsed as an outer relation. An inner
+		 * relation and join clauses are converted to EXISTS condition and
+		 * passed to the upper level.
 		 */
-		appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
-						 get_jointype_name(fpinfo->jointype), join_sql_i.data);
-
-		/* Append join clause; (TRUE) if no join clause */
-		if (fpinfo->joinclauses)
+		if (fpinfo->jointype == JOIN_SEMI)
 		{
-			deparse_expr_cxt context;
+			appendStringInfo(buf, "%s", join_sql_o.data);
+		}
+		else
+		{
+			/*
+			 * For a join relation FROM clause entry is deparsed as
+			 *
+			 * ((outer relation) <join type> (inner relation) ON
+			 * (joinclauses))
+			 */
+			appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
+							 get_jointype_name(fpinfo->jointype), join_sql_i.data);
+
+			/* Append join clause; (TRUE) if no join clause */
+			if (fpinfo->joinclauses)
+			{
+				deparse_expr_cxt context;
 
-			context.buf = buf;
-			context.foreignrel = foreignrel;
-			context.scanrel = foreignrel;
-			context.root = root;
-			context.params_list = params_list;
+				context.buf = buf;
+				context.foreignrel = foreignrel;
+				context.scanrel = foreignrel;
+				context.root = root;
+				context.params_list = params_list;
 
-			appendStringInfoChar(buf, '(');
-			appendConditions(fpinfo->joinclauses, &context);
+				appendStringInfoChar(buf, '(');
+				appendConditions(fpinfo->joinclauses, &context);
+				appendStringInfoChar(buf, ')');
+			}
+			else
+				appendStringInfoString(buf, "(TRUE)");
+
+			/* End the FROM clause entry. */
 			appendStringInfoChar(buf, ')');
 		}
-		else
-			appendStringInfoString(buf, "(TRUE)");
 
-		/* End the FROM clause entry. */
-		appendStringInfoChar(buf, ')');
+		/*
+		 * Construct addl_conds from current level addl_conds and addl_conds,
+		 * coming from inner and outer rels.
+		 */
+		need_and = false;
+		if (addl_conds->len > 0)
+			need_and = true;
+		if (addl_conds_o.len > 0)
+		{
+			if (need_and)
+				appendStringInfoString(addl_conds, " AND ");
+			appendStringInfoString(addl_conds, addl_conds_o.data);
+			need_and = true;
+		}
+		if (addl_conds_i.len > 0)
+		{
+			if (need_and)
+				appendStringInfoString(addl_conds, " AND ");
+			appendStringInfoString(addl_conds, addl_conds_i.data);
+		}
+		pfree(addl_conds_i.data);
+		pfree(addl_conds_o.data);
 	}
 	else
 	{
@@ -1867,7 +1970,7 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 static void
 deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				   bool make_subquery, Index ignore_rel, List **ignore_conds,
-				   List **params_list)
+				   StringInfo addl_conds, List **params_list)
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
@@ -1925,7 +2028,7 @@ deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 	}
 	else
 		deparseFromExprForRel(buf, root, foreignrel, true, ignore_rel,
-							  ignore_conds, params_list);
+							  ignore_conds, addl_conds, params_list);
 }
 
 /*
@@ -2148,6 +2251,7 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 	RangeTblEntry *rte = planner_rt_fetch(rtindex, root);
 	ListCell   *lc,
 			   *lc2;
+	StringInfoData addl_conds;
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -2185,21 +2289,21 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 
 	reset_transmission_modes(nestlevel);
 
+	initStringInfo(&addl_conds);
+
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 	{
 		List	   *ignore_conds = NIL;
 
+
 		appendStringInfoString(buf, " FROM ");
 		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
-							  &ignore_conds, params_list);
+							  &ignore_conds, &addl_conds, params_list);
 		remote_conds = list_concat(remote_conds, ignore_conds);
 	}
 
-	if (remote_conds)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(remote_conds, &context);
-	}
+	appendWhereClause(remote_conds, &addl_conds, &context);
+	pfree(addl_conds.data);
 
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		deparseExplicitTargetList(returningList, true, retrieved_attrs,
@@ -2255,6 +2359,7 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 					   List **retrieved_attrs)
 {
 	deparse_expr_cxt context;
+	StringInfoData addl_conds;
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -2268,21 +2373,20 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		appendStringInfo(buf, " %s%d", REL_ALIAS_PREFIX, rtindex);
 
+	initStringInfo(&addl_conds);
+
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 	{
 		List	   *ignore_conds = NIL;
 
 		appendStringInfoString(buf, " USING ");
 		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
-							  &ignore_conds, params_list);
+							  &ignore_conds, &addl_conds, params_list);
 		remote_conds = list_concat(remote_conds, ignore_conds);
 	}
 
-	if (remote_conds)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(remote_conds, &context);
-	}
+	appendWhereClause(remote_conds, &addl_conds, &context);
+	pfree(addl_conds.data);
 
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		deparseExplicitTargetList(returningList, true, retrieved_attrs,
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 558e94b8450..bab8155c092 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -2000,23 +2000,16 @@ SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER B
    Remote SQL: SELECT r1.ctid, CASE WHEN (r1.*)::text IS NOT NULL THEN ROW(r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8) END, CASE WHEN (r2.*)::text IS NOT NULL THEN ROW(r2."C 1", r2.c2, r2.c3, r2.c4, r2.c5, r2.c6, r2.c7, r2.c8) END, r1."C 1", r1.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r2."C 1" = r1."C 1")))) ORDER BY r1.c3 ASC NULLS LAST, r1."C 1" ASC NULLS LAST LIMIT 10::bigint OFFSET 100::bigint
 (4 rows)
 
--- SEMI JOIN, not pushed down
+-- SEMI JOIN
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
-                                      QUERY PLAN                                       
----------------------------------------------------------------------------------------
- Limit
+                                                                                              QUERY PLAN                                                                                               
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
    Output: t1.c1
-   ->  Merge Semi Join
-         Output: t1.c1
-         Merge Cond: (t1.c1 = t2.c1)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1
-               Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-         ->  Foreign Scan on public.ft2 t2
-               Output: t2.c1
-               Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-(11 rows)
+   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
+   Remote SQL: SELECT r1."C 1" FROM "S 1"."T 1" r1 WHERE (EXISTS (SELECT NULL FROM "S 1"."T 1" r2 WHERE ((r2."C 1" = r1."C 1")))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint OFFSET 100::bigint
+(4 rows)
 
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
  c1  
@@ -4000,23 +3993,13 @@ EXECUTE st2(101, 121);
 -- subquery using immutable function (can be sent to remote)
 PREPARE st3(int) AS SELECT * FROM ft1 t1 WHERE t1.c1 < $2 AND t1.c3 IN (SELECT c3 FROM ft2 t2 WHERE c1 > $1 AND date(c5) = '1970-01-17'::date) ORDER BY c1;
 EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st3(10, 20);
-                                                      QUERY PLAN                                                       
------------------------------------------------------------------------------------------------------------------------
- Sort
+                                                                                                                                            QUERY PLAN                                                                                                                                             
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
    Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-   Sort Key: t1.c1
-   ->  Nested Loop Semi Join
-         Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-         Join Filter: (t2.c3 = t1.c3)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-               Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" WHERE (("C 1" < 20))
-         ->  Materialize
-               Output: t2.c3
-               ->  Foreign Scan on public.ft2 t2
-                     Output: t2.c3
-                     Remote SQL: SELECT c3 FROM "S 1"."T 1" WHERE (("C 1" > 10)) AND ((date(c5) = '1970-01-17'::date))
-(14 rows)
+   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" < 20)) AND (EXISTS (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r3."C 1" > 10)) AND ((date(r3.c5) = '1970-01-17'::date)) AND ((r3.c3 = r1.c3)))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
 
 EXECUTE st3(10, 20);
  c1 | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
@@ -4560,6 +4543,260 @@ explain (verbose, costs off) select * from ft3 f, loct3 l
                Index Cond: (l.f1 = 'foo'::text)
 (12 rows)
 
+-- ===================================================================
+-- test SEMI-JOIN pushdown
+-- ===================================================================
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+                                                                                                                                                 QUERY PLAN                                                                                                                                                  
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r2.c1, r2.c2, r2.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r2 ON (((r1.c2 = r2.c1)) AND ((r1."C 1" > 900)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 4" r4 WHERE ((r1.c2 = r4.c1)))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 916 |  6 | 00916 | Sat Jan 17 00:00:00 1970 PST | Sat Jan 17 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 926 |  6 | 00926 | Tue Jan 27 00:00:00 1970 PST | Tue Jan 27 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 936 |  6 | 00936 | Fri Feb 06 00:00:00 1970 PST | Fri Feb 06 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 946 |  6 | 00946 | Mon Feb 16 00:00:00 1970 PST | Mon Feb 16 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 956 |  6 | 00956 | Thu Feb 26 00:00:00 1970 PST | Thu Feb 26 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 966 |  6 | 00966 | Sun Mar 08 00:00:00 1970 PST | Sun Mar 08 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 976 |  6 | 00976 | Wed Mar 18 00:00:00 1970 PST | Wed Mar 18 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 986 |  6 | 00986 | Sat Mar 28 00:00:00 1970 PST | Sat Mar 28 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 996 |  6 | 00996 | Tue Apr 07 00:00:00 1970 PST | Tue Apr 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- The same query, different join order
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+                                                                                                                                                 QUERY PLAN                                                                                                                                                  
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r4.c1, r4.c2, r4.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r4 ON (((r1.c2 = r4.c1)) AND ((r1."C 1" > 900)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 4" r5 WHERE ((r4.c1 = r5.c1)))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 916 |  6 | 00916 | Sat Jan 17 00:00:00 1970 PST | Sat Jan 17 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 926 |  6 | 00926 | Tue Jan 27 00:00:00 1970 PST | Tue Jan 27 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 936 |  6 | 00936 | Fri Feb 06 00:00:00 1970 PST | Fri Feb 06 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 946 |  6 | 00946 | Mon Feb 16 00:00:00 1970 PST | Mon Feb 16 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 956 |  6 | 00956 | Thu Feb 26 00:00:00 1970 PST | Thu Feb 26 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 966 |  6 | 00966 | Sun Mar 08 00:00:00 1970 PST | Sun Mar 08 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 976 |  6 | 00976 | Wed Mar 18 00:00:00 1970 PST | Wed Mar 18 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 986 |  6 | 00986 | Sat Mar 28 00:00:00 1970 PST | Sat Mar 28 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 996 |  6 | 00996 | Tue Apr 07 00:00:00 1970 PST | Tue Apr 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- Left join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                   QUERY PLAN                                                                                                                                                                                   
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: (public.ft2) LEFT JOIN ((public.ft4) SEMI JOIN (public.ft5))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, s6.c1, s6.c2, s6.c3 FROM ("S 1"."T 1" r1 LEFT JOIN (SELECT r4.c1, r4.c2, r4.c3 FROM "S 1"."T 3" r4 WHERE (EXISTS (SELECT NULL FROM "S 1"."T 4" r5 WHERE ((r4.c1 = r5.c1))))) s6(c1, c2, c3) ON (((r1.c2 = s6.c1)))) WHERE ((r1."C 1" > 900)) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 901 |  1 | 00901 | Fri Jan 02 00:00:00 1970 PST | Fri Jan 02 00:00:00 1970 | 1  | 1          | foo |    |    | 
+ 902 |  2 | 00902 | Sat Jan 03 00:00:00 1970 PST | Sat Jan 03 00:00:00 1970 | 2  | 2          | foo |    |    | 
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo |    |    | 
+ 904 |  4 | 00904 | Mon Jan 05 00:00:00 1970 PST | Mon Jan 05 00:00:00 1970 | 4  | 4          | foo |    |    | 
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo |    |    | 
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo |    |    | 
+ 908 |  8 | 00908 | Fri Jan 09 00:00:00 1970 PST | Fri Jan 09 00:00:00 1970 | 8  | 8          | foo |    |    | 
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo |    |    | 
+ 910 |  0 | 00910 | Sun Jan 11 00:00:00 1970 PST | Sun Jan 11 00:00:00 1970 | 0  | 0          | foo |    |    | 
+(10 rows)
+
+-- Several semi-joins per upper level join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                                                      QUERY PLAN                                                                                                                                                                                                                       
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)) INNER JOIN (public.ft5 ft5_1)) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r6.c1, r6.c2, r6.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r6 ON (((r1.c2 = r6.c1)) AND ((r1."C 1" > 900)))) INNER JOIN "S 1"."T 4" r8 ON (((r1.c2 <= r8.c1)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 3" r9 WHERE ((r8.c1 = r9.c1))) AND EXISTS (SELECT NULL FROM "S 1"."T 4" r7 WHERE ((r6.c1 = r7.c1)))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- Semi-join below Semi-join
+EXPLAIN (verbose, costs off)
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                            QUERY PLAN                                                                                                                                                             
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8
+   Relations: (public.ft2) SEMI JOIN ((public.ft2 ft2_1) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" > 900)) AND (EXISTS (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r1."C 1" = r3."C 1")) AND (EXISTS (SELECT NULL FROM "S 1"."T 3" r4 WHERE ((r3.c2 = r4.c2)))))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
+-----+----+-------+------------------------------+--------------------------+----+------------+-----
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo
+ 913 |  3 | 00913 | Wed Jan 14 00:00:00 1970 PST | Wed Jan 14 00:00:00 1970 | 3  | 3          | foo
+ 915 |  5 | 00915 | Fri Jan 16 00:00:00 1970 PST | Fri Jan 16 00:00:00 1970 | 5  | 5          | foo
+ 917 |  7 | 00917 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 919 |  9 | 00919 | Tue Jan 20 00:00:00 1970 PST | Tue Jan 20 00:00:00 1970 | 9  | 9          | foo
+ 923 |  3 | 00923 | Sat Jan 24 00:00:00 1970 PST | Sat Jan 24 00:00:00 1970 | 3  | 3          | foo
+ 925 |  5 | 00925 | Mon Jan 26 00:00:00 1970 PST | Mon Jan 26 00:00:00 1970 | 5  | 5          | foo
+(10 rows)
+
+-- Upper level relations shouldn't refer EXISTS() subqueries
+EXPLAIN (verbose, costs off)
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1=ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+                                                                                                                                                            QUERY PLAN                                                                                                                                                             
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ftupper.c1, ftupper.c2, ftupper.c3, ftupper.c4, ftupper.c5, ftupper.c6, ftupper.c7, ftupper.c8
+   Relations: (public.ft2 ftupper) SEMI JOIN ((public.ft2) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" > 900)) AND (EXISTS (SELECT NULL FROM "S 1"."T 1" r2 WHERE ((r1."C 1" = r2."C 1")) AND (EXISTS (SELECT NULL FROM "S 1"."T 3" r3 WHERE ((r2.c2 = r3.c2)))))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1=ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
+-----+----+-------+------------------------------+--------------------------+----+------------+-----
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo
+ 913 |  3 | 00913 | Wed Jan 14 00:00:00 1970 PST | Wed Jan 14 00:00:00 1970 | 3  | 3          | foo
+ 915 |  5 | 00915 | Fri Jan 16 00:00:00 1970 PST | Fri Jan 16 00:00:00 1970 | 5  | 5          | foo
+ 917 |  7 | 00917 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 919 |  9 | 00919 | Tue Jan 20 00:00:00 1970 PST | Tue Jan 20 00:00:00 1970 | 9  | 9          | foo
+ 923 |  3 | 00923 | Sat Jan 24 00:00:00 1970 PST | Sat Jan 24 00:00:00 1970 | 3  | 3          | foo
+ 925 |  5 | 00925 | Mon Jan 26 00:00:00 1970 PST | Mon Jan 26 00:00:00 1970 | 5  | 5          | foo
+(10 rows)
+
+-- EXISTS should be propogated to the highest upper inner join
+EXPLAIN (verbose, costs off)
+	SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2=ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2=ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                                                      QUERY PLAN                                                                                                                                                                                                                      
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft2 ft2_1)) INNER JOIN (public.ft2 ft2_2)) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r6.c1, r6.c2, r6.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r6 ON (((r1.c2 = r6.c1)) AND ((r1."C 1" > 900)))) INNER JOIN "S 1"."T 1" r8 ON (((r1.c2 = r8.c2)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 3" r9 WHERE ((r1.c2 = r9.c2))) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r7 WHERE ((r7.c2 = r6.c2)))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2=ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2=ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+ c1 | c2 | c3 | c4 | c5 | c6 | c7 | c8 | c1 | c2 | c3 
+----+----+----+----+----+----+----+----+----+----+----
+(0 rows)
+
 -- ===================================================================
 -- test writable foreign table stuff
 -- ===================================================================
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 8d7500abfbd..d0f5466c629 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -778,6 +778,7 @@ postgresGetForeignRelSize(PlannerInfo *root,
 	fpinfo->make_outerrel_subquery = false;
 	fpinfo->make_innerrel_subquery = false;
 	fpinfo->lower_subquery_rels = NULL;
+	fpinfo->unknown_subquery_rels = NULL;
 	/* Set the relation index. */
 	fpinfo->relation_index = baserel->relid;
 }
@@ -5515,6 +5516,37 @@ postgresImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
 	return commands;
 }
 
+/*
+ * Check if reltarget is safe enough to push down such join
+ */
+static bool
+joinrel_target_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype, RelOptInfo *outerrel, RelOptInfo *innerrel)
+{
+	List	   *vars;
+	ListCell   *lc;
+	bool		ok = true;
+
+	Assert(joinrel->reltarget);
+
+	vars = pull_var_clause((Node *) joinrel->reltarget->exprs, PVC_INCLUDE_PLACEHOLDERS);
+
+	foreach(lc, vars)
+	{
+		Var		   *var = (Var *) lfirst(lc);
+
+		if (IsA(var, Var))
+		{
+			if (jointype == JOIN_SEMI && bms_is_member(var->varno, innerrel->relids) && !bms_is_member(var->varno, outerrel->relids))
+			{
+				/* We deparse semi-join as exists() subquery, and so can't deparse references to inner rel in join target list. */
+				ok = false;
+				break;
+			}
+		}
+	}
+	return ok;
+}
+
 /*
  * Assess whether the join between inner and outer relations can be pushed down
  * to the foreign server. As a side effect, save information we obtain in this
@@ -5532,12 +5564,19 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	List	   *joinclauses;
 
 	/*
-	 * We support pushing down INNER, LEFT, RIGHT and FULL OUTER joins.
-	 * Constructing queries representing SEMI and ANTI joins is hard, hence
+	 * We support pushing down INNER, LEFT, RIGHT, FULL OUTER and SEMI joins.
+	 * Constructing queries representing ANTI joins is hard, hence
 	 * not considered right now.
 	 */
 	if (jointype != JOIN_INNER && jointype != JOIN_LEFT &&
-		jointype != JOIN_RIGHT && jointype != JOIN_FULL)
+		jointype != JOIN_RIGHT && jointype != JOIN_FULL &&
+		jointype != JOIN_SEMI)
+		return false;
+
+	/*
+	 * We can't push down join if its reltarget is not safe
+	 */
+	if (!joinrel_target_ok(root, joinrel, jointype, outerrel, innerrel))
 		return false;
 
 	/*
@@ -5649,6 +5688,8 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	Assert(bms_is_subset(fpinfo_i->lower_subquery_rels, innerrel->relids));
 	fpinfo->lower_subquery_rels = bms_union(fpinfo_o->lower_subquery_rels,
 											fpinfo_i->lower_subquery_rels);
+	fpinfo->unknown_subquery_rels = bms_union(fpinfo_o->unknown_subquery_rels,
+											fpinfo_i->unknown_subquery_rels);
 
 	/*
 	 * Pull the other remote conditions from the joining relations into join
@@ -5692,6 +5733,16 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 											   fpinfo_i->remote_conds);
 			break;
 
+		case JOIN_SEMI:
+			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+											  fpinfo_i->remote_conds);
+			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+											   fpinfo->remote_conds);
+			fpinfo->remote_conds = list_copy(fpinfo_o->remote_conds);
+			fpinfo->unknown_subquery_rels = bms_union(fpinfo->unknown_subquery_rels,
+											innerrel->relids);
+			break;
+
 		case JOIN_FULL:
 
 			/*
@@ -5734,6 +5785,24 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 		fpinfo->joinclauses = fpinfo->remote_conds;
 		fpinfo->remote_conds = NIL;
 	}
+	else if (jointype == JOIN_LEFT || jointype == JOIN_RIGHT || jointype == JOIN_FULL)
+	{
+		/*
+		 * Conditions, generated from semi-joins, should
+		 * be evaluated before LEFT/RIGHT/FULL join.
+		 */
+		if (!bms_is_empty(fpinfo_o->unknown_subquery_rels))
+		{
+			fpinfo->make_outerrel_subquery = true;
+			fpinfo->lower_subquery_rels = bms_add_members(fpinfo->lower_subquery_rels, outerrel->relids);
+		}
+
+		if (!bms_is_empty(fpinfo_i->unknown_subquery_rels))
+		{
+			fpinfo->make_innerrel_subquery = true;
+			fpinfo->lower_subquery_rels = bms_add_members(fpinfo->lower_subquery_rels, innerrel->relids);
+		}
+	}
 
 	/* Mark that this join can be pushed down safely */
 	fpinfo->pushdown_safe = true;
@@ -7467,6 +7536,8 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 {
 	ListCell   *lc;
 
+	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
+
 	foreach(lc, ec->ec_members)
 	{
 		EquivalenceMember *em = (EquivalenceMember *) lfirst(lc);
@@ -7477,6 +7548,7 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 		 */
 		if (bms_is_subset(em->em_relids, rel->relids) &&
 			!bms_is_empty(em->em_relids) &&
+			bms_is_empty(bms_intersect(em->em_relids, fpinfo->unknown_subquery_rels)) &&
 			is_foreign_expr(root, rel, em->em_expr))
 			return em;
 	}
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index a11d45bedfc..dc5835a5bad 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -118,7 +118,8 @@ typedef struct PgFdwRelationInfo
 										 * subquery? */
 	Relids		lower_subquery_rels;	/* all relids appearing in lower
 										 * subqueries */
-
+	Relids		unknown_subquery_rels;	/* relids, which can't be referred to
+										 * from upper relations */
 	/*
 	 * Index of the relation.  It is used to create an alias to a subquery
 	 * representing the relation.
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index b0dbb41fb55..bb73ca2009a 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -599,7 +599,7 @@ WITH t (c1_1, c1_3, c2_1) AS MATERIALIZED (SELECT t1.c1, t1.c3, t2.c1 FROM ft1 t
 -- ctid with whole-row reference
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER BY t1.c3, t1.c1 OFFSET 100 LIMIT 10;
--- SEMI JOIN, not pushed down
+-- SEMI JOIN
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
@@ -1272,6 +1272,123 @@ explain (verbose, costs off) select * from ft3 where f2 = 'foo' COLLATE "C";
 explain (verbose, costs off) select * from ft3 f, loct3 l
   where f.f3 = l.f3 COLLATE "POSIX" and l.f1 = 'foo';
 
+-- ===================================================================
+-- test SEMI-JOIN pushdown
+-- ===================================================================
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+
+-- The same query, different join order
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+
+-- Left join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Several semi-joins per upper level join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Semi-join below Semi-join
+EXPLAIN (verbose, costs off)
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Upper level relations shouldn't refer EXISTS() subqueries
+EXPLAIN (verbose, costs off)
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1=ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1=ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+
+-- EXISTS should be propogated to the highest upper inner join
+EXPLAIN (verbose, costs off)
+	SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2=ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2=ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2=ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2=ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+
 -- ===================================================================
 -- test writable foreign table stuff
 -- ===================================================================
-- 
2.34.1

From 0f26b0841cb095b4e114984deac2b1b001368c15 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <a.pyhalov@postgrespro.ru>
Date: Mon, 7 Nov 2022 10:23:32 +0300
Subject: [PATCH v3] postgres_fdw: add support for deparsing semi joins

We deparse semi-joins as EXISTS subqueries. So, deparsing
semi-join leads to generating addl_conds condition,
which is then added to the uppermost JOIN's WHERE clause.
---
 contrib/postgres_fdw/deparse.c                | 201 +++++++++---
 .../postgres_fdw/expected/postgres_fdw.out    | 297 ++++++++++++++++--
 contrib/postgres_fdw/postgres_fdw.c           |  82 ++++-
 contrib/postgres_fdw/postgres_fdw.h           |   3 +-
 contrib/postgres_fdw/sql/postgres_fdw.sql     | 119 ++++++-
 5 files changed, 620 insertions(+), 82 deletions(-)

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index 95247656504..10d82d9f2ab 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -179,12 +179,13 @@ static void appendLimitClause(deparse_expr_cxt *context);
 static void appendConditions(List *exprs, deparse_expr_cxt *context);
 static void deparseFromExprForRel(StringInfo buf, PlannerInfo *root,
 								  RelOptInfo *foreignrel, bool use_alias,
-								  Index ignore_rel, List **ignore_conds,
+								  Index ignore_rel, List **ignore_conds, StringInfo addl_conds,
 								  List **params_list);
+static void appendWhereClause(List *exprs, StringInfo addl_conds, deparse_expr_cxt *context);
 static void deparseFromExpr(List *quals, deparse_expr_cxt *context);
 static void deparseRangeTblRef(StringInfo buf, PlannerInfo *root,
 							   RelOptInfo *foreignrel, bool make_subquery,
-							   Index ignore_rel, List **ignore_conds, List **params_list);
+							   Index ignore_rel, List **ignore_conds, StringInfo addl_conds, List **params_list);
 static void deparseAggref(Aggref *node, deparse_expr_cxt *context);
 static void appendGroupByClause(List *tlist, deparse_expr_cxt *context);
 static void appendOrderBySuffix(Oid sortop, Oid sortcoltype, bool nulls_first,
@@ -1370,23 +1371,20 @@ deparseFromExpr(List *quals, deparse_expr_cxt *context)
 {
 	StringInfo	buf = context->buf;
 	RelOptInfo *scanrel = context->scanrel;
+	StringInfoData addl_conds;
 
 	/* For upper relations, scanrel must be either a joinrel or a baserel */
 	Assert(!IS_UPPER_REL(context->foreignrel) ||
 		   IS_JOIN_REL(scanrel) || IS_SIMPLE_REL(scanrel));
 
+	initStringInfo(&addl_conds);
 	/* Construct FROM clause */
 	appendStringInfoString(buf, " FROM ");
 	deparseFromExprForRel(buf, context->root, scanrel,
 						  (bms_membership(scanrel->relids) == BMS_MULTIPLE),
-						  (Index) 0, NULL, context->params_list);
-
-	/* Construct WHERE clause */
-	if (quals != NIL)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(quals, context);
-	}
+						  (Index) 0, NULL, &addl_conds, context->params_list);
+	appendWhereClause(quals, &addl_conds, context);
+	pfree(addl_conds.data);
 }
 
 /*
@@ -1598,6 +1596,33 @@ appendConditions(List *exprs, deparse_expr_cxt *context)
 	reset_transmission_modes(nestlevel);
 }
 
+/*
+ * Append WHERE clause, containing conditions
+ * from exprs and addl_conds, to context->buf.
+ */
+static void
+appendWhereClause(List *exprs, StringInfo addl_conds, deparse_expr_cxt *context)
+{
+	StringInfo	buf = context->buf;
+	bool		need_and = false;
+
+	if (exprs != NIL || addl_conds->len > 0)
+		appendStringInfoString(buf, " WHERE ");
+
+	if (exprs != NIL)
+	{
+		appendConditions(exprs, context);
+		need_and = true;
+	}
+
+	if (addl_conds->len > 0)
+	{
+		if (need_and)
+			appendStringInfoString(buf, " AND ");
+		appendStringInfo(buf, "(%s)", addl_conds->data);
+	}
+}
+
 /* Output join name for given join type */
 const char *
 get_jointype_name(JoinType jointype)
@@ -1616,6 +1641,9 @@ get_jointype_name(JoinType jointype)
 		case JOIN_FULL:
 			return "FULL";
 
+		case JOIN_SEMI:
+			return "SEMI";
+
 		default:
 			/* Shouldn't come here, but protect from buggy code. */
 			elog(ERROR, "unsupported join type %d", jointype);
@@ -1712,10 +1740,13 @@ deparseSubqueryTargetList(deparse_expr_cxt *context)
  * of DELETE; it deparses the join relation as if the relation never contained
  * the target relation, and creates a List of conditions to be deparsed into
  * the top-level WHERE clause, which is returned to *ignore_conds.
+ *
+ * 'addl_conds' is a initialized StringInfo. If some additional conditions
+ * should be appended to WHERE clause, they are returned as addl_conds.
  */
 static void
 deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
-					  bool use_alias, Index ignore_rel, List **ignore_conds,
+					  bool use_alias, Index ignore_rel, List **ignore_conds, StringInfo addl_conds,
 					  List **params_list)
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
@@ -1728,6 +1759,9 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		RelOptInfo *innerrel = fpinfo->innerrel;
 		bool		outerrel_is_target = false;
 		bool		innerrel_is_target = false;
+		StringInfoData addl_conds_i;
+		StringInfoData addl_conds_o;
+		bool		need_and;
 
 		if (ignore_rel > 0 && bms_is_member(ignore_rel, foreignrel->relids))
 		{
@@ -1761,10 +1795,11 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		/* Deparse outer relation if not the target relation. */
 		if (!outerrel_is_target)
 		{
+			initStringInfo(&addl_conds_o);
 			initStringInfo(&join_sql_o);
 			deparseRangeTblRef(&join_sql_o, root, outerrel,
 							   fpinfo->make_outerrel_subquery,
-							   ignore_rel, ignore_conds, params_list);
+							   ignore_rel, ignore_conds, &addl_conds_o, params_list);
 
 			/*
 			 * If inner relation is the target relation, skip deparsing it.
@@ -1780,6 +1815,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				Assert(fpinfo->jointype == JOIN_INNER);
 				Assert(fpinfo->joinclauses == NIL);
 				appendBinaryStringInfo(buf, join_sql_o.data, join_sql_o.len);
+				if (addl_conds_o.len > 0)
+				{
+					Assert(addl_conds->len == 0);
+					appendStringInfoString(addl_conds, addl_conds_o.data);
+				}
+				pfree(addl_conds_o.data);
 				return;
 			}
 		}
@@ -1787,10 +1828,33 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		/* Deparse inner relation if not the target relation. */
 		if (!innerrel_is_target)
 		{
+			initStringInfo(&addl_conds_i);
+
 			initStringInfo(&join_sql_i);
 			deparseRangeTblRef(&join_sql_i, root, innerrel,
 							   fpinfo->make_innerrel_subquery,
-							   ignore_rel, ignore_conds, params_list);
+							   ignore_rel, ignore_conds, &addl_conds_i, params_list);
+
+			if (fpinfo->jointype == JOIN_SEMI)
+			{
+				deparse_expr_cxt context;
+
+				appendStringInfo(addl_conds, "EXISTS (SELECT NULL FROM %s", join_sql_i.data);
+
+				context.buf = addl_conds;
+				context.foreignrel = foreignrel;
+				context.scanrel = foreignrel;
+				context.root = root;
+				context.params_list = params_list;
+
+				appendWhereClause(fpinfo->joinclauses, &addl_conds_i, &context);
+
+				if (addl_conds_i.len > 0)
+					resetStringInfo(&addl_conds_i);
+
+				/* Close parentheses for EXISTS subquery */
+				appendStringInfo(addl_conds, ")");
+			}
 
 			/*
 			 * If outer relation is the target relation, skip deparsing it.
@@ -1801,6 +1865,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				Assert(fpinfo->jointype == JOIN_INNER);
 				Assert(fpinfo->joinclauses == NIL);
 				appendBinaryStringInfo(buf, join_sql_i.data, join_sql_i.len);
+				if (addl_conds_i.len > 0)
+				{
+					Assert(addl_conds->len == 0);
+					appendStringInfoString(addl_conds, addl_conds_i.data);
+				}
+				pfree(addl_conds_i.data);
 				return;
 			}
 		}
@@ -1809,33 +1879,69 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		Assert(!outerrel_is_target && !innerrel_is_target);
 
 		/*
-		 * For a join relation FROM clause entry is deparsed as
-		 *
-		 * ((outer relation) <join type> (inner relation) ON (joinclauses))
+		 * For semijoin FROM clause is deparsed as an outer relation. An inner
+		 * relation and join clauses are converted to EXISTS condition and
+		 * passed to the upper level.
 		 */
-		appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
-						 get_jointype_name(fpinfo->jointype), join_sql_i.data);
-
-		/* Append join clause; (TRUE) if no join clause */
-		if (fpinfo->joinclauses)
+		if (fpinfo->jointype == JOIN_SEMI)
 		{
-			deparse_expr_cxt context;
+			appendStringInfo(buf, "%s", join_sql_o.data);
+		}
+		else
+		{
+			/*
+			 * For a join relation FROM clause entry is deparsed as
+			 *
+			 * ((outer relation) <join type> (inner relation) ON
+			 * (joinclauses))
+			 */
+			appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
+							 get_jointype_name(fpinfo->jointype), join_sql_i.data);
+
+			/* Append join clause; (TRUE) if no join clause */
+			if (fpinfo->joinclauses)
+			{
+				deparse_expr_cxt context;
 
-			context.buf = buf;
-			context.foreignrel = foreignrel;
-			context.scanrel = foreignrel;
-			context.root = root;
-			context.params_list = params_list;
+				context.buf = buf;
+				context.foreignrel = foreignrel;
+				context.scanrel = foreignrel;
+				context.root = root;
+				context.params_list = params_list;
 
-			appendStringInfoChar(buf, '(');
-			appendConditions(fpinfo->joinclauses, &context);
+				appendStringInfoChar(buf, '(');
+				appendConditions(fpinfo->joinclauses, &context);
+				appendStringInfoChar(buf, ')');
+			}
+			else
+				appendStringInfoString(buf, "(TRUE)");
+
+			/* End the FROM clause entry. */
 			appendStringInfoChar(buf, ')');
 		}
-		else
-			appendStringInfoString(buf, "(TRUE)");
 
-		/* End the FROM clause entry. */
-		appendStringInfoChar(buf, ')');
+		/*
+		 * Construct addl_conds from current level addl_conds and addl_conds,
+		 * coming from inner and outer rels.
+		 */
+		need_and = false;
+		if (addl_conds->len > 0)
+			need_and = true;
+		if (addl_conds_o.len > 0)
+		{
+			if (need_and)
+				appendStringInfoString(addl_conds, " AND ");
+			appendStringInfoString(addl_conds, addl_conds_o.data);
+			need_and = true;
+		}
+		if (addl_conds_i.len > 0)
+		{
+			if (need_and)
+				appendStringInfoString(addl_conds, " AND ");
+			appendStringInfoString(addl_conds, addl_conds_i.data);
+		}
+		pfree(addl_conds_i.data);
+		pfree(addl_conds_o.data);
 	}
 	else
 	{
@@ -1867,7 +1973,7 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 static void
 deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				   bool make_subquery, Index ignore_rel, List **ignore_conds,
-				   List **params_list)
+				   StringInfo addl_conds, List **params_list)
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
@@ -1925,7 +2031,7 @@ deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 	}
 	else
 		deparseFromExprForRel(buf, root, foreignrel, true, ignore_rel,
-							  ignore_conds, params_list);
+							  ignore_conds, addl_conds, params_list);
 }
 
 /*
@@ -2148,6 +2254,7 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 	RangeTblEntry *rte = planner_rt_fetch(rtindex, root);
 	ListCell   *lc,
 			   *lc2;
+	StringInfoData addl_conds;
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -2185,21 +2292,21 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 
 	reset_transmission_modes(nestlevel);
 
+	initStringInfo(&addl_conds);
+
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 	{
 		List	   *ignore_conds = NIL;
 
+
 		appendStringInfoString(buf, " FROM ");
 		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
-							  &ignore_conds, params_list);
+							  &ignore_conds, &addl_conds, params_list);
 		remote_conds = list_concat(remote_conds, ignore_conds);
 	}
 
-	if (remote_conds)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(remote_conds, &context);
-	}
+	appendWhereClause(remote_conds, &addl_conds, &context);
+	pfree(addl_conds.data);
 
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		deparseExplicitTargetList(returningList, true, retrieved_attrs,
@@ -2255,6 +2362,7 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 					   List **retrieved_attrs)
 {
 	deparse_expr_cxt context;
+	StringInfoData addl_conds;
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -2268,21 +2376,20 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		appendStringInfo(buf, " %s%d", REL_ALIAS_PREFIX, rtindex);
 
+	initStringInfo(&addl_conds);
+
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 	{
 		List	   *ignore_conds = NIL;
 
 		appendStringInfoString(buf, " USING ");
 		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
-							  &ignore_conds, params_list);
+							  &ignore_conds, &addl_conds, params_list);
 		remote_conds = list_concat(remote_conds, ignore_conds);
 	}
 
-	if (remote_conds)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(remote_conds, &context);
-	}
+	appendWhereClause(remote_conds, &addl_conds, &context);
+	pfree(addl_conds.data);
 
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		deparseExplicitTargetList(returningList, true, retrieved_attrs,
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 2ab3f1efaa0..340a1efcd44 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -2000,23 +2000,16 @@ SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER B
    Remote SQL: SELECT r1.ctid, CASE WHEN (r1.*)::text IS NOT NULL THEN ROW(r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8) END, CASE WHEN (r2.*)::text IS NOT NULL THEN ROW(r2."C 1", r2.c2, r2.c3, r2.c4, r2.c5, r2.c6, r2.c7, r2.c8) END, r1."C 1", r1.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r2."C 1" = r1."C 1")))) ORDER BY r1.c3 ASC NULLS LAST, r1."C 1" ASC NULLS LAST LIMIT 10::bigint OFFSET 100::bigint
 (4 rows)
 
--- SEMI JOIN, not pushed down
+-- SEMI JOIN
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
-                                      QUERY PLAN                                       
----------------------------------------------------------------------------------------
- Limit
+                                                                                              QUERY PLAN                                                                                               
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
    Output: t1.c1
-   ->  Merge Semi Join
-         Output: t1.c1
-         Merge Cond: (t1.c1 = t2.c1)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1
-               Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-         ->  Foreign Scan on public.ft2 t2
-               Output: t2.c1
-               Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-(11 rows)
+   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
+   Remote SQL: SELECT r1."C 1" FROM "S 1"."T 1" r1 WHERE (EXISTS (SELECT NULL FROM "S 1"."T 1" r2 WHERE ((r2."C 1" = r1."C 1")))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint OFFSET 100::bigint
+(4 rows)
 
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
  c1  
@@ -4000,23 +3993,13 @@ EXECUTE st2(101, 121);
 -- subquery using immutable function (can be sent to remote)
 PREPARE st3(int) AS SELECT * FROM ft1 t1 WHERE t1.c1 < $2 AND t1.c3 IN (SELECT c3 FROM ft2 t2 WHERE c1 > $1 AND date(c5) = '1970-01-17'::date) ORDER BY c1;
 EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st3(10, 20);
-                                                      QUERY PLAN                                                       
------------------------------------------------------------------------------------------------------------------------
- Sort
+                                                                                                                                            QUERY PLAN                                                                                                                                             
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
    Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-   Sort Key: t1.c1
-   ->  Nested Loop Semi Join
-         Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-         Join Filter: (t2.c3 = t1.c3)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-               Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" WHERE (("C 1" < 20))
-         ->  Materialize
-               Output: t2.c3
-               ->  Foreign Scan on public.ft2 t2
-                     Output: t2.c3
-                     Remote SQL: SELECT c3 FROM "S 1"."T 1" WHERE (("C 1" > 10)) AND ((date(c5) = '1970-01-17'::date))
-(14 rows)
+   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" < 20)) AND (EXISTS (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r3."C 1" > 10)) AND ((date(r3.c5) = '1970-01-17'::date)) AND ((r3.c3 = r1.c3)))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
 
 EXECUTE st3(10, 20);
  c1 | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
@@ -4560,6 +4543,260 @@ explain (verbose, costs off) select * from ft3 f, loct3 l
                Index Cond: (l.f1 = 'foo'::text)
 (12 rows)
 
+-- ===================================================================
+-- test SEMI-JOIN pushdown
+-- ===================================================================
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+                                                                                                                                                 QUERY PLAN                                                                                                                                                  
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r2.c1, r2.c2, r2.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r2 ON (((r1.c2 = r2.c1)) AND ((r1."C 1" > 900)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 4" r4 WHERE ((r1.c2 = r4.c1)))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 916 |  6 | 00916 | Sat Jan 17 00:00:00 1970 PST | Sat Jan 17 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 926 |  6 | 00926 | Tue Jan 27 00:00:00 1970 PST | Tue Jan 27 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 936 |  6 | 00936 | Fri Feb 06 00:00:00 1970 PST | Fri Feb 06 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 946 |  6 | 00946 | Mon Feb 16 00:00:00 1970 PST | Mon Feb 16 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 956 |  6 | 00956 | Thu Feb 26 00:00:00 1970 PST | Thu Feb 26 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 966 |  6 | 00966 | Sun Mar 08 00:00:00 1970 PST | Sun Mar 08 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 976 |  6 | 00976 | Wed Mar 18 00:00:00 1970 PST | Wed Mar 18 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 986 |  6 | 00986 | Sat Mar 28 00:00:00 1970 PST | Sat Mar 28 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 996 |  6 | 00996 | Tue Apr 07 00:00:00 1970 PST | Tue Apr 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- The same query, different join order
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+                                                                                                                                                 QUERY PLAN                                                                                                                                                  
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r4.c1, r4.c2, r4.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r4 ON (((r1.c2 = r4.c1)) AND ((r1."C 1" > 900)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 4" r5 WHERE ((r4.c1 = r5.c1)))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 916 |  6 | 00916 | Sat Jan 17 00:00:00 1970 PST | Sat Jan 17 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 926 |  6 | 00926 | Tue Jan 27 00:00:00 1970 PST | Tue Jan 27 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 936 |  6 | 00936 | Fri Feb 06 00:00:00 1970 PST | Fri Feb 06 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 946 |  6 | 00946 | Mon Feb 16 00:00:00 1970 PST | Mon Feb 16 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 956 |  6 | 00956 | Thu Feb 26 00:00:00 1970 PST | Thu Feb 26 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 966 |  6 | 00966 | Sun Mar 08 00:00:00 1970 PST | Sun Mar 08 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 976 |  6 | 00976 | Wed Mar 18 00:00:00 1970 PST | Wed Mar 18 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 986 |  6 | 00986 | Sat Mar 28 00:00:00 1970 PST | Sat Mar 28 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 996 |  6 | 00996 | Tue Apr 07 00:00:00 1970 PST | Tue Apr 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- Left join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                   QUERY PLAN                                                                                                                                                                                   
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: (public.ft2) LEFT JOIN ((public.ft4) SEMI JOIN (public.ft5))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, s6.c1, s6.c2, s6.c3 FROM ("S 1"."T 1" r1 LEFT JOIN (SELECT r4.c1, r4.c2, r4.c3 FROM "S 1"."T 3" r4 WHERE (EXISTS (SELECT NULL FROM "S 1"."T 4" r5 WHERE ((r4.c1 = r5.c1))))) s6(c1, c2, c3) ON (((r1.c2 = s6.c1)))) WHERE ((r1."C 1" > 900)) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 901 |  1 | 00901 | Fri Jan 02 00:00:00 1970 PST | Fri Jan 02 00:00:00 1970 | 1  | 1          | foo |    |    | 
+ 902 |  2 | 00902 | Sat Jan 03 00:00:00 1970 PST | Sat Jan 03 00:00:00 1970 | 2  | 2          | foo |    |    | 
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo |    |    | 
+ 904 |  4 | 00904 | Mon Jan 05 00:00:00 1970 PST | Mon Jan 05 00:00:00 1970 | 4  | 4          | foo |    |    | 
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo |    |    | 
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo |    |    | 
+ 908 |  8 | 00908 | Fri Jan 09 00:00:00 1970 PST | Fri Jan 09 00:00:00 1970 | 8  | 8          | foo |    |    | 
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo |    |    | 
+ 910 |  0 | 00910 | Sun Jan 11 00:00:00 1970 PST | Sun Jan 11 00:00:00 1970 | 0  | 0          | foo |    |    | 
+(10 rows)
+
+-- Several semi-joins per upper level join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                                                      QUERY PLAN                                                                                                                                                                                                                       
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)) INNER JOIN (public.ft5 ft5_1)) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r6.c1, r6.c2, r6.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r6 ON (((r1.c2 = r6.c1)) AND ((r1."C 1" > 900)))) INNER JOIN "S 1"."T 4" r8 ON (((r1.c2 <= r8.c1)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 3" r9 WHERE ((r8.c1 = r9.c1))) AND EXISTS (SELECT NULL FROM "S 1"."T 4" r7 WHERE ((r6.c1 = r7.c1)))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- Semi-join below Semi-join
+EXPLAIN (verbose, costs off)
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                            QUERY PLAN                                                                                                                                                             
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8
+   Relations: (public.ft2) SEMI JOIN ((public.ft2 ft2_1) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" > 900)) AND (EXISTS (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r1."C 1" = r3."C 1")) AND (EXISTS (SELECT NULL FROM "S 1"."T 3" r4 WHERE ((r3.c2 = r4.c2)))))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
+-----+----+-------+------------------------------+--------------------------+----+------------+-----
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo
+ 913 |  3 | 00913 | Wed Jan 14 00:00:00 1970 PST | Wed Jan 14 00:00:00 1970 | 3  | 3          | foo
+ 915 |  5 | 00915 | Fri Jan 16 00:00:00 1970 PST | Fri Jan 16 00:00:00 1970 | 5  | 5          | foo
+ 917 |  7 | 00917 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 919 |  9 | 00919 | Tue Jan 20 00:00:00 1970 PST | Tue Jan 20 00:00:00 1970 | 9  | 9          | foo
+ 923 |  3 | 00923 | Sat Jan 24 00:00:00 1970 PST | Sat Jan 24 00:00:00 1970 | 3  | 3          | foo
+ 925 |  5 | 00925 | Mon Jan 26 00:00:00 1970 PST | Mon Jan 26 00:00:00 1970 | 5  | 5          | foo
+(10 rows)
+
+-- Upper level relations shouldn't refer EXISTS() subqueries
+EXPLAIN (verbose, costs off)
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+                                                                                                                                                            QUERY PLAN                                                                                                                                                             
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ftupper.c1, ftupper.c2, ftupper.c3, ftupper.c4, ftupper.c5, ftupper.c6, ftupper.c7, ftupper.c8
+   Relations: (public.ft2 ftupper) SEMI JOIN ((public.ft2) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" > 900)) AND (EXISTS (SELECT NULL FROM "S 1"."T 1" r2 WHERE ((r1."C 1" = r2."C 1")) AND (EXISTS (SELECT NULL FROM "S 1"."T 3" r3 WHERE ((r2.c2 = r3.c2)))))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
+-----+----+-------+------------------------------+--------------------------+----+------------+-----
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo
+ 913 |  3 | 00913 | Wed Jan 14 00:00:00 1970 PST | Wed Jan 14 00:00:00 1970 | 3  | 3          | foo
+ 915 |  5 | 00915 | Fri Jan 16 00:00:00 1970 PST | Fri Jan 16 00:00:00 1970 | 5  | 5          | foo
+ 917 |  7 | 00917 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 919 |  9 | 00919 | Tue Jan 20 00:00:00 1970 PST | Tue Jan 20 00:00:00 1970 | 9  | 9          | foo
+ 923 |  3 | 00923 | Sat Jan 24 00:00:00 1970 PST | Sat Jan 24 00:00:00 1970 | 3  | 3          | foo
+ 925 |  5 | 00925 | Mon Jan 26 00:00:00 1970 PST | Mon Jan 26 00:00:00 1970 | 5  | 5          | foo
+(10 rows)
+
+-- EXISTS should be propogated to the highest upper inner join
+EXPLAIN (verbose, costs off)
+	SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                                                      QUERY PLAN                                                                                                                                                                                                                      
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft2 ft2_1)) INNER JOIN (public.ft2 ft2_2)) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r6.c1, r6.c2, r6.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r6 ON (((r1.c2 = r6.c1)) AND ((r1."C 1" > 900)))) INNER JOIN "S 1"."T 1" r8 ON (((r1.c2 = r8.c2)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 3" r9 WHERE ((r1.c2 = r9.c2))) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r7 WHERE ((r7.c2 = r6.c2)))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+ c1 | c2 | c3 | c4 | c5 | c6 | c7 | c8 | c1 | c2 | c3 
+----+----+----+----+----+----+----+----+----+----+----
+(0 rows)
+
 -- ===================================================================
 -- test writable foreign table stuff
 -- ===================================================================
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 20c7b1ad05a..29f725bbae1 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -778,6 +778,7 @@ postgresGetForeignRelSize(PlannerInfo *root,
 	fpinfo->make_outerrel_subquery = false;
 	fpinfo->make_innerrel_subquery = false;
 	fpinfo->lower_subquery_rels = NULL;
+	fpinfo->unknown_subquery_rels = NULL;
 	/* Set the relation index. */
 	fpinfo->relation_index = baserel->relid;
 }
@@ -5511,6 +5512,41 @@ postgresImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
 	return commands;
 }
 
+/*
+ * Check if reltarget is safe enough to push down such join
+ */
+static bool
+joinrel_target_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype, RelOptInfo *outerrel, RelOptInfo *innerrel)
+{
+	List	   *vars;
+	ListCell   *lc;
+	bool		ok = true;
+
+	Assert(joinrel->reltarget);
+
+	vars = pull_var_clause((Node *) joinrel->reltarget->exprs, PVC_INCLUDE_PLACEHOLDERS);
+
+	foreach(lc, vars)
+	{
+		Var		   *var = (Var *) lfirst(lc);
+
+		if (IsA(var, Var))
+		{
+			if (jointype == JOIN_SEMI && bms_is_member(var->varno, innerrel->relids) && !bms_is_member(var->varno, outerrel->relids))
+			{
+				/*
+				 * Planner can create semi-joins, which refer to inner rel vars in its
+				 * target list. However, we deparse semi-join as exists() subquery,
+				 * so can't handle references to inner rel in target list.
+				 */
+				ok = false;
+				break;
+			}
+		}
+	}
+	return ok;
+}
+
 /*
  * Assess whether the join between inner and outer relations can be pushed down
  * to the foreign server. As a side effect, save information we obtain in this
@@ -5528,12 +5564,19 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	List	   *joinclauses;
 
 	/*
-	 * We support pushing down INNER, LEFT, RIGHT and FULL OUTER joins.
-	 * Constructing queries representing SEMI and ANTI joins is hard, hence
+	 * We support pushing down INNER, LEFT, RIGHT, FULL OUTER and SEMI joins.
+	 * Constructing queries representing ANTI joins is hard, hence
 	 * not considered right now.
 	 */
 	if (jointype != JOIN_INNER && jointype != JOIN_LEFT &&
-		jointype != JOIN_RIGHT && jointype != JOIN_FULL)
+		jointype != JOIN_RIGHT && jointype != JOIN_FULL &&
+		jointype != JOIN_SEMI)
+		return false;
+
+	/*
+	 * We can't push down join if its reltarget is not safe
+	 */
+	if (!joinrel_target_ok(root, joinrel, jointype, outerrel, innerrel))
 		return false;
 
 	/*
@@ -5645,6 +5688,8 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	Assert(bms_is_subset(fpinfo_i->lower_subquery_rels, innerrel->relids));
 	fpinfo->lower_subquery_rels = bms_union(fpinfo_o->lower_subquery_rels,
 											fpinfo_i->lower_subquery_rels);
+	fpinfo->unknown_subquery_rels = bms_union(fpinfo_o->unknown_subquery_rels,
+											fpinfo_i->unknown_subquery_rels);
 
 	/*
 	 * Pull the other remote conditions from the joining relations into join
@@ -5688,6 +5733,16 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 											   fpinfo_i->remote_conds);
 			break;
 
+		case JOIN_SEMI:
+			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+											  fpinfo_i->remote_conds);
+			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+											   fpinfo->remote_conds);
+			fpinfo->remote_conds = list_copy(fpinfo_o->remote_conds);
+			fpinfo->unknown_subquery_rels = bms_union(fpinfo->unknown_subquery_rels,
+											innerrel->relids);
+			break;
+
 		case JOIN_FULL:
 
 			/*
@@ -5730,6 +5785,24 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 		fpinfo->joinclauses = fpinfo->remote_conds;
 		fpinfo->remote_conds = NIL;
 	}
+	else if (jointype == JOIN_LEFT || jointype == JOIN_RIGHT || jointype == JOIN_FULL)
+	{
+		/*
+		 * Conditions, generated from semi-joins, should
+		 * be evaluated before LEFT/RIGHT/FULL join.
+		 */
+		if (!bms_is_empty(fpinfo_o->unknown_subquery_rels))
+		{
+			fpinfo->make_outerrel_subquery = true;
+			fpinfo->lower_subquery_rels = bms_add_members(fpinfo->lower_subquery_rels, outerrel->relids);
+		}
+
+		if (!bms_is_empty(fpinfo_i->unknown_subquery_rels))
+		{
+			fpinfo->make_innerrel_subquery = true;
+			fpinfo->lower_subquery_rels = bms_add_members(fpinfo->lower_subquery_rels, innerrel->relids);
+		}
+	}
 
 	/* Mark that this join can be pushed down safely */
 	fpinfo->pushdown_safe = true;
@@ -7463,6 +7536,8 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 {
 	ListCell   *lc;
 
+	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
+
 	foreach(lc, ec->ec_members)
 	{
 		EquivalenceMember *em = (EquivalenceMember *) lfirst(lc);
@@ -7473,6 +7548,7 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 		 */
 		if (bms_is_subset(em->em_relids, rel->relids) &&
 			!bms_is_empty(em->em_relids) &&
+			bms_is_empty(bms_intersect(em->em_relids, fpinfo->unknown_subquery_rels)) &&
 			is_foreign_expr(root, rel, em->em_expr))
 			return em;
 	}
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index a11d45bedfc..dc5835a5bad 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -118,7 +118,8 @@ typedef struct PgFdwRelationInfo
 										 * subquery? */
 	Relids		lower_subquery_rels;	/* all relids appearing in lower
 										 * subqueries */
-
+	Relids		unknown_subquery_rels;	/* relids, which can't be referred to
+										 * from upper relations */
 	/*
 	 * Index of the relation.  It is used to create an alias to a subquery
 	 * representing the relation.
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 51560429e06..18672968de3 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -599,7 +599,7 @@ WITH t (c1_1, c1_3, c2_1) AS MATERIALIZED (SELECT t1.c1, t1.c3, t2.c1 FROM ft1 t
 -- ctid with whole-row reference
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER BY t1.c3, t1.c1 OFFSET 100 LIMIT 10;
--- SEMI JOIN, not pushed down
+-- SEMI JOIN
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
@@ -1272,6 +1272,123 @@ explain (verbose, costs off) select * from ft3 where f2 = 'foo' COLLATE "C";
 explain (verbose, costs off) select * from ft3 f, loct3 l
   where f.f3 = l.f3 COLLATE "POSIX" and l.f1 = 'foo';
 
+-- ===================================================================
+-- test SEMI-JOIN pushdown
+-- ===================================================================
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+
+-- The same query, different join order
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+
+-- Left join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Several semi-joins per upper level join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Semi-join below Semi-join
+EXPLAIN (verbose, costs off)
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Upper level relations shouldn't refer EXISTS() subqueries
+EXPLAIN (verbose, costs off)
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+
+-- EXISTS should be propogated to the highest upper inner join
+EXPLAIN (verbose, costs off)
+	SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+
 -- ===================================================================
 -- test writable foreign table stuff
 -- ===================================================================
-- 
2.34.1

From f37d26d9b622767f94e89034fa8e4fccc69e358d Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <a.pyhalov@postgrespro.ru>
Date: Mon, 7 Nov 2022 10:23:32 +0300
Subject: [PATCH v4] postgres_fdw: add support for deparsing semi joins

We deparse semi-joins as EXISTS subqueries. So, deparsing
semi-join leads to generating addl_conds condition,
which is then added to the uppermost JOIN's WHERE clause.
---
 contrib/postgres_fdw/deparse.c                | 206 +++++++++---
 .../postgres_fdw/expected/postgres_fdw.out    | 297 ++++++++++++++++--
 contrib/postgres_fdw/postgres_fdw.c           |  89 +++++-
 contrib/postgres_fdw/postgres_fdw.h           |   2 +
 contrib/postgres_fdw/sql/postgres_fdw.sql     | 119 ++++++-
 5 files changed, 632 insertions(+), 81 deletions(-)

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index 473fa45bd43..1217d47050b 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -180,11 +180,14 @@ static void appendConditions(List *exprs, deparse_expr_cxt *context);
 static void deparseFromExprForRel(StringInfo buf, PlannerInfo *root,
 								  RelOptInfo *foreignrel, bool use_alias,
 								  Index ignore_rel, List **ignore_conds,
+								  StringInfo additional_conds,
 								  List **params_list);
+static void appendWhereClause(List *exprs, StringInfo additional_conds, deparse_expr_cxt *context);
 static void deparseFromExpr(List *quals, deparse_expr_cxt *context);
 static void deparseRangeTblRef(StringInfo buf, PlannerInfo *root,
 							   RelOptInfo *foreignrel, bool make_subquery,
-							   Index ignore_rel, List **ignore_conds, List **params_list);
+							   Index ignore_rel, List **ignore_conds,
+							   StringInfo additional_conds, List **params_list);
 static void deparseAggref(Aggref *node, deparse_expr_cxt *context);
 static void appendGroupByClause(List *tlist, deparse_expr_cxt *context);
 static void appendOrderBySuffix(Oid sortop, Oid sortcoltype, bool nulls_first,
@@ -1370,23 +1373,21 @@ deparseFromExpr(List *quals, deparse_expr_cxt *context)
 {
 	StringInfo	buf = context->buf;
 	RelOptInfo *scanrel = context->scanrel;
+	StringInfoData additional_conds;
 
 	/* For upper relations, scanrel must be either a joinrel or a baserel */
 	Assert(!IS_UPPER_REL(context->foreignrel) ||
 		   IS_JOIN_REL(scanrel) || IS_SIMPLE_REL(scanrel));
 
+	initStringInfo(&additional_conds);
 	/* Construct FROM clause */
 	appendStringInfoString(buf, " FROM ");
 	deparseFromExprForRel(buf, context->root, scanrel,
 						  (bms_membership(scanrel->relids) == BMS_MULTIPLE),
-						  (Index) 0, NULL, context->params_list);
-
-	/* Construct WHERE clause */
-	if (quals != NIL)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(quals, context);
-	}
+						  (Index) 0, NULL, &additional_conds,
+						  context->params_list);
+	appendWhereClause(quals, &additional_conds, context);
+	pfree(additional_conds.data);
 }
 
 /*
@@ -1598,6 +1599,33 @@ appendConditions(List *exprs, deparse_expr_cxt *context)
 	reset_transmission_modes(nestlevel);
 }
 
+/*
+ * Append WHERE clause, containing conditions
+ * from exprs and additional_conds, to context->buf.
+ */
+static void
+appendWhereClause(List *exprs, StringInfo additional_conds, deparse_expr_cxt *context)
+{
+	StringInfo	buf = context->buf;
+	bool		need_and = false;
+
+	if (exprs != NIL || additional_conds->len > 0)
+		appendStringInfoString(buf, " WHERE ");
+
+	if (exprs != NIL)
+	{
+		appendConditions(exprs, context);
+		need_and = true;
+	}
+
+	if (additional_conds->len > 0)
+	{
+		if (need_and)
+			appendStringInfoString(buf, " AND ");
+		appendStringInfo(buf, "(%s)", additional_conds->data);
+	}
+}
+
 /* Output join name for given join type */
 const char *
 get_jointype_name(JoinType jointype)
@@ -1616,6 +1644,9 @@ get_jointype_name(JoinType jointype)
 		case JOIN_FULL:
 			return "FULL";
 
+		case JOIN_SEMI:
+			return "SEMI";
+
 		default:
 			/* Shouldn't come here, but protect from buggy code. */
 			elog(ERROR, "unsupported join type %d", jointype);
@@ -1712,11 +1743,14 @@ deparseSubqueryTargetList(deparse_expr_cxt *context)
  * of DELETE; it deparses the join relation as if the relation never contained
  * the target relation, and creates a List of conditions to be deparsed into
  * the top-level WHERE clause, which is returned to *ignore_conds.
+ *
+ * 'additional_conds' is a initialized StringInfo. If some additional conditions
+ * should be appended to WHERE clause, they are returned as additional_conds.
  */
 static void
 deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 					  bool use_alias, Index ignore_rel, List **ignore_conds,
-					  List **params_list)
+					  StringInfo additional_conds, List **params_list)
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
@@ -1728,6 +1762,9 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		RelOptInfo *innerrel = fpinfo->innerrel;
 		bool		outerrel_is_target = false;
 		bool		innerrel_is_target = false;
+		StringInfoData additional_conds_i;
+		StringInfoData additional_conds_o;
+		bool		need_and;
 
 		if (ignore_rel > 0 && bms_is_member(ignore_rel, foreignrel->relids))
 		{
@@ -1761,10 +1798,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		/* Deparse outer relation if not the target relation. */
 		if (!outerrel_is_target)
 		{
+			initStringInfo(&additional_conds_o);
 			initStringInfo(&join_sql_o);
 			deparseRangeTblRef(&join_sql_o, root, outerrel,
 							   fpinfo->make_outerrel_subquery,
-							   ignore_rel, ignore_conds, params_list);
+							   ignore_rel, ignore_conds, &additional_conds_o,
+							   params_list);
 
 			/*
 			 * If inner relation is the target relation, skip deparsing it.
@@ -1780,6 +1819,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				Assert(fpinfo->jointype == JOIN_INNER);
 				Assert(fpinfo->joinclauses == NIL);
 				appendBinaryStringInfo(buf, join_sql_o.data, join_sql_o.len);
+				if (additional_conds_o.len > 0)
+				{
+					Assert(additional_conds->len == 0);
+					appendStringInfoString(additional_conds, additional_conds_o.data);
+				}
+				pfree(additional_conds_o.data);
 				return;
 			}
 		}
@@ -1787,10 +1832,35 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		/* Deparse inner relation if not the target relation. */
 		if (!innerrel_is_target)
 		{
+			initStringInfo(&additional_conds_i);
+
 			initStringInfo(&join_sql_i);
 			deparseRangeTblRef(&join_sql_i, root, innerrel,
 							   fpinfo->make_innerrel_subquery,
-							   ignore_rel, ignore_conds, params_list);
+							   ignore_rel, ignore_conds, &additional_conds_i,
+							   params_list);
+
+			if (fpinfo->jointype == JOIN_SEMI)
+			{
+				deparse_expr_cxt context;
+
+				appendStringInfo(additional_conds, "EXISTS (SELECT NULL FROM %s",
+								 join_sql_i.data);
+
+				context.buf = additional_conds;
+				context.foreignrel = foreignrel;
+				context.scanrel = foreignrel;
+				context.root = root;
+				context.params_list = params_list;
+
+				appendWhereClause(fpinfo->joinclauses, &additional_conds_i, &context);
+
+				if (additional_conds_i.len > 0)
+					resetStringInfo(&additional_conds_i);
+
+				/* Close parentheses for EXISTS subquery */
+				appendStringInfo(additional_conds, ")");
+			}
 
 			/*
 			 * If outer relation is the target relation, skip deparsing it.
@@ -1801,6 +1871,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				Assert(fpinfo->jointype == JOIN_INNER);
 				Assert(fpinfo->joinclauses == NIL);
 				appendBinaryStringInfo(buf, join_sql_i.data, join_sql_i.len);
+				if (additional_conds_i.len > 0)
+				{
+					Assert(additional_conds->len == 0);
+					appendStringInfoString(additional_conds, additional_conds_i.data);
+				}
+				pfree(additional_conds_i.data);
 				return;
 			}
 		}
@@ -1809,33 +1885,69 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		Assert(!outerrel_is_target && !innerrel_is_target);
 
 		/*
-		 * For a join relation FROM clause entry is deparsed as
-		 *
-		 * ((outer relation) <join type> (inner relation) ON (joinclauses))
+		 * For semijoin FROM clause is deparsed as an outer relation. An inner
+		 * relation and join clauses are converted to EXISTS condition and
+		 * passed to the upper level.
 		 */
-		appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
-						 get_jointype_name(fpinfo->jointype), join_sql_i.data);
-
-		/* Append join clause; (TRUE) if no join clause */
-		if (fpinfo->joinclauses)
+		if (fpinfo->jointype == JOIN_SEMI)
 		{
-			deparse_expr_cxt context;
+			appendStringInfo(buf, "%s", join_sql_o.data);
+		}
+		else
+		{
+			/*
+			 * For a join relation FROM clause entry is deparsed as
+			 *
+			 * ((outer relation) <join type> (inner relation) ON
+			 * (joinclauses))
+			 */
+			appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
+							 get_jointype_name(fpinfo->jointype), join_sql_i.data);
+
+			/* Append join clause; (TRUE) if no join clause */
+			if (fpinfo->joinclauses)
+			{
+				deparse_expr_cxt context;
 
-			context.buf = buf;
-			context.foreignrel = foreignrel;
-			context.scanrel = foreignrel;
-			context.root = root;
-			context.params_list = params_list;
+				context.buf = buf;
+				context.foreignrel = foreignrel;
+				context.scanrel = foreignrel;
+				context.root = root;
+				context.params_list = params_list;
 
-			appendStringInfoChar(buf, '(');
-			appendConditions(fpinfo->joinclauses, &context);
+				appendStringInfoChar(buf, '(');
+				appendConditions(fpinfo->joinclauses, &context);
+				appendStringInfoChar(buf, ')');
+			}
+			else
+				appendStringInfoString(buf, "(TRUE)");
+
+			/* End the FROM clause entry. */
 			appendStringInfoChar(buf, ')');
 		}
-		else
-			appendStringInfoString(buf, "(TRUE)");
 
-		/* End the FROM clause entry. */
-		appendStringInfoChar(buf, ')');
+		/*
+		 * Construct additional_conds from current level additional_conds and
+		 * additional_conds, coming from inner and outer rels.
+		 */
+		need_and = false;
+		if (additional_conds->len > 0)
+			need_and = true;
+		if (additional_conds_o.len > 0)
+		{
+			if (need_and)
+				appendStringInfoString(additional_conds, " AND ");
+			appendStringInfoString(additional_conds, additional_conds_o.data);
+			need_and = true;
+		}
+		if (additional_conds_i.len > 0)
+		{
+			if (need_and)
+				appendStringInfoString(additional_conds, " AND ");
+			appendStringInfoString(additional_conds, additional_conds_i.data);
+		}
+		pfree(additional_conds_i.data);
+		pfree(additional_conds_o.data);
 	}
 	else
 	{
@@ -1867,7 +1979,7 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 static void
 deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				   bool make_subquery, Index ignore_rel, List **ignore_conds,
-				   List **params_list)
+				   StringInfo additional_conds, List **params_list)
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
@@ -1925,7 +2037,8 @@ deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 	}
 	else
 		deparseFromExprForRel(buf, root, foreignrel, true, ignore_rel,
-							  ignore_conds, params_list);
+							  ignore_conds, additional_conds,
+							  params_list);
 }
 
 /*
@@ -2148,6 +2261,7 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 	RangeTblEntry *rte = planner_rt_fetch(rtindex, root);
 	ListCell   *lc,
 			   *lc2;
+	StringInfoData additional_conds;
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -2185,21 +2299,21 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 
 	reset_transmission_modes(nestlevel);
 
+	initStringInfo(&additional_conds);
+
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 	{
 		List	   *ignore_conds = NIL;
 
+
 		appendStringInfoString(buf, " FROM ");
 		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
-							  &ignore_conds, params_list);
+							  &ignore_conds, &additional_conds, params_list);
 		remote_conds = list_concat(remote_conds, ignore_conds);
 	}
 
-	if (remote_conds)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(remote_conds, &context);
-	}
+	appendWhereClause(remote_conds, &additional_conds, &context);
+	pfree(additional_conds.data);
 
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		deparseExplicitTargetList(returningList, true, retrieved_attrs,
@@ -2255,6 +2369,7 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 					   List **retrieved_attrs)
 {
 	deparse_expr_cxt context;
+	StringInfoData additional_conds;
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -2268,21 +2383,20 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		appendStringInfo(buf, " %s%d", REL_ALIAS_PREFIX, rtindex);
 
+	initStringInfo(&additional_conds);
+
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 	{
 		List	   *ignore_conds = NIL;
 
 		appendStringInfoString(buf, " USING ");
 		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
-							  &ignore_conds, params_list);
+							  &ignore_conds, &additional_conds, params_list);
 		remote_conds = list_concat(remote_conds, ignore_conds);
 	}
 
-	if (remote_conds)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(remote_conds, &context);
-	}
+	appendWhereClause(remote_conds, &additional_conds, &context);
+	pfree(additional_conds.data);
 
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		deparseExplicitTargetList(returningList, true, retrieved_attrs,
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 2350cfe1487..75a9acee522 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -2000,23 +2000,16 @@ SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER B
    Remote SQL: SELECT r1.ctid, CASE WHEN (r1.*)::text IS NOT NULL THEN ROW(r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8) END, CASE WHEN (r2.*)::text IS NOT NULL THEN ROW(r2."C 1", r2.c2, r2.c3, r2.c4, r2.c5, r2.c6, r2.c7, r2.c8) END, r1."C 1", r1.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r2."C 1" = r1."C 1")))) ORDER BY r1.c3 ASC NULLS LAST, r1."C 1" ASC NULLS LAST LIMIT 10::bigint OFFSET 100::bigint
 (4 rows)
 
--- SEMI JOIN, not pushed down
+-- SEMI JOIN
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
-                                      QUERY PLAN                                       
----------------------------------------------------------------------------------------
- Limit
+                                                                                              QUERY PLAN                                                                                               
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
    Output: t1.c1
-   ->  Merge Semi Join
-         Output: t1.c1
-         Merge Cond: (t1.c1 = t2.c1)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1
-               Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-         ->  Foreign Scan on public.ft2 t2
-               Output: t2.c1
-               Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-(11 rows)
+   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
+   Remote SQL: SELECT r1."C 1" FROM "S 1"."T 1" r1 WHERE (EXISTS (SELECT NULL FROM "S 1"."T 1" r2 WHERE ((r2."C 1" = r1."C 1")))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint OFFSET 100::bigint
+(4 rows)
 
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
  c1  
@@ -3996,23 +3989,13 @@ EXECUTE st2(101, 121);
 -- subquery using immutable function (can be sent to remote)
 PREPARE st3(int) AS SELECT * FROM ft1 t1 WHERE t1.c1 < $2 AND t1.c3 IN (SELECT c3 FROM ft2 t2 WHERE c1 > $1 AND date(c5) = '1970-01-17'::date) ORDER BY c1;
 EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st3(10, 20);
-                                                      QUERY PLAN                                                       
------------------------------------------------------------------------------------------------------------------------
- Sort
+                                                                                                                                            QUERY PLAN                                                                                                                                             
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
    Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-   Sort Key: t1.c1
-   ->  Nested Loop Semi Join
-         Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-         Join Filter: (t2.c3 = t1.c3)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-               Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" WHERE (("C 1" < 20))
-         ->  Materialize
-               Output: t2.c3
-               ->  Foreign Scan on public.ft2 t2
-                     Output: t2.c3
-                     Remote SQL: SELECT c3 FROM "S 1"."T 1" WHERE (("C 1" > 10)) AND ((date(c5) = '1970-01-17'::date))
-(14 rows)
+   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" < 20)) AND (EXISTS (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r3."C 1" > 10)) AND ((date(r3.c5) = '1970-01-17'::date)) AND ((r3.c3 = r1.c3)))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
 
 EXECUTE st3(10, 20);
  c1 | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
@@ -4556,6 +4539,260 @@ explain (verbose, costs off) select * from ft3 f, loct3 l
                Index Cond: (l.f1 = 'foo'::text)
 (12 rows)
 
+-- ===================================================================
+-- test SEMI-JOIN pushdown
+-- ===================================================================
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+                                                                                                                                                 QUERY PLAN                                                                                                                                                  
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r2.c1, r2.c2, r2.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r2 ON (((r1.c2 = r2.c1)) AND ((r1."C 1" > 900)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 4" r4 WHERE ((r1.c2 = r4.c1)))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 916 |  6 | 00916 | Sat Jan 17 00:00:00 1970 PST | Sat Jan 17 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 926 |  6 | 00926 | Tue Jan 27 00:00:00 1970 PST | Tue Jan 27 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 936 |  6 | 00936 | Fri Feb 06 00:00:00 1970 PST | Fri Feb 06 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 946 |  6 | 00946 | Mon Feb 16 00:00:00 1970 PST | Mon Feb 16 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 956 |  6 | 00956 | Thu Feb 26 00:00:00 1970 PST | Thu Feb 26 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 966 |  6 | 00966 | Sun Mar 08 00:00:00 1970 PST | Sun Mar 08 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 976 |  6 | 00976 | Wed Mar 18 00:00:00 1970 PST | Wed Mar 18 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 986 |  6 | 00986 | Sat Mar 28 00:00:00 1970 PST | Sat Mar 28 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 996 |  6 | 00996 | Tue Apr 07 00:00:00 1970 PST | Tue Apr 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- The same query, different join order
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+                                                                                                                                                 QUERY PLAN                                                                                                                                                  
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r4.c1, r4.c2, r4.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r4 ON (((r1.c2 = r4.c1)) AND ((r1."C 1" > 900)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 4" r5 WHERE ((r4.c1 = r5.c1)))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 916 |  6 | 00916 | Sat Jan 17 00:00:00 1970 PST | Sat Jan 17 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 926 |  6 | 00926 | Tue Jan 27 00:00:00 1970 PST | Tue Jan 27 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 936 |  6 | 00936 | Fri Feb 06 00:00:00 1970 PST | Fri Feb 06 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 946 |  6 | 00946 | Mon Feb 16 00:00:00 1970 PST | Mon Feb 16 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 956 |  6 | 00956 | Thu Feb 26 00:00:00 1970 PST | Thu Feb 26 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 966 |  6 | 00966 | Sun Mar 08 00:00:00 1970 PST | Sun Mar 08 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 976 |  6 | 00976 | Wed Mar 18 00:00:00 1970 PST | Wed Mar 18 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 986 |  6 | 00986 | Sat Mar 28 00:00:00 1970 PST | Sat Mar 28 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 996 |  6 | 00996 | Tue Apr 07 00:00:00 1970 PST | Tue Apr 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- Left join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                   QUERY PLAN                                                                                                                                                                                   
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: (public.ft2) LEFT JOIN ((public.ft4) SEMI JOIN (public.ft5))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, s6.c1, s6.c2, s6.c3 FROM ("S 1"."T 1" r1 LEFT JOIN (SELECT r4.c1, r4.c2, r4.c3 FROM "S 1"."T 3" r4 WHERE (EXISTS (SELECT NULL FROM "S 1"."T 4" r5 WHERE ((r4.c1 = r5.c1))))) s6(c1, c2, c3) ON (((r1.c2 = s6.c1)))) WHERE ((r1."C 1" > 900)) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 901 |  1 | 00901 | Fri Jan 02 00:00:00 1970 PST | Fri Jan 02 00:00:00 1970 | 1  | 1          | foo |    |    | 
+ 902 |  2 | 00902 | Sat Jan 03 00:00:00 1970 PST | Sat Jan 03 00:00:00 1970 | 2  | 2          | foo |    |    | 
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo |    |    | 
+ 904 |  4 | 00904 | Mon Jan 05 00:00:00 1970 PST | Mon Jan 05 00:00:00 1970 | 4  | 4          | foo |    |    | 
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo |    |    | 
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo |    |    | 
+ 908 |  8 | 00908 | Fri Jan 09 00:00:00 1970 PST | Fri Jan 09 00:00:00 1970 | 8  | 8          | foo |    |    | 
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo |    |    | 
+ 910 |  0 | 00910 | Sun Jan 11 00:00:00 1970 PST | Sun Jan 11 00:00:00 1970 | 0  | 0          | foo |    |    | 
+(10 rows)
+
+-- Several semi-joins per upper level join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                                                      QUERY PLAN                                                                                                                                                                                                                       
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)) INNER JOIN (public.ft5 ft5_1)) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r6.c1, r6.c2, r6.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r6 ON (((r1.c2 = r6.c1)) AND ((r1."C 1" > 900)))) INNER JOIN "S 1"."T 4" r8 ON (((r1.c2 <= r8.c1)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 3" r9 WHERE ((r8.c1 = r9.c1))) AND EXISTS (SELECT NULL FROM "S 1"."T 4" r7 WHERE ((r6.c1 = r7.c1)))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- Semi-join below Semi-join
+EXPLAIN (verbose, costs off)
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                            QUERY PLAN                                                                                                                                                             
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8
+   Relations: (public.ft2) SEMI JOIN ((public.ft2 ft2_1) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" > 900)) AND (EXISTS (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r1."C 1" = r3."C 1")) AND (EXISTS (SELECT NULL FROM "S 1"."T 3" r4 WHERE ((r3.c2 = r4.c2)))))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
+-----+----+-------+------------------------------+--------------------------+----+------------+-----
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo
+ 913 |  3 | 00913 | Wed Jan 14 00:00:00 1970 PST | Wed Jan 14 00:00:00 1970 | 3  | 3          | foo
+ 915 |  5 | 00915 | Fri Jan 16 00:00:00 1970 PST | Fri Jan 16 00:00:00 1970 | 5  | 5          | foo
+ 917 |  7 | 00917 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 919 |  9 | 00919 | Tue Jan 20 00:00:00 1970 PST | Tue Jan 20 00:00:00 1970 | 9  | 9          | foo
+ 923 |  3 | 00923 | Sat Jan 24 00:00:00 1970 PST | Sat Jan 24 00:00:00 1970 | 3  | 3          | foo
+ 925 |  5 | 00925 | Mon Jan 26 00:00:00 1970 PST | Mon Jan 26 00:00:00 1970 | 5  | 5          | foo
+(10 rows)
+
+-- Upper level relations shouldn't refer EXISTS() subqueries
+EXPLAIN (verbose, costs off)
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+                                                                                                                                                            QUERY PLAN                                                                                                                                                             
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ftupper.c1, ftupper.c2, ftupper.c3, ftupper.c4, ftupper.c5, ftupper.c6, ftupper.c7, ftupper.c8
+   Relations: (public.ft2 ftupper) SEMI JOIN ((public.ft2) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" > 900)) AND (EXISTS (SELECT NULL FROM "S 1"."T 1" r2 WHERE ((r1."C 1" = r2."C 1")) AND (EXISTS (SELECT NULL FROM "S 1"."T 3" r3 WHERE ((r2.c2 = r3.c2)))))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
+-----+----+-------+------------------------------+--------------------------+----+------------+-----
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo
+ 913 |  3 | 00913 | Wed Jan 14 00:00:00 1970 PST | Wed Jan 14 00:00:00 1970 | 3  | 3          | foo
+ 915 |  5 | 00915 | Fri Jan 16 00:00:00 1970 PST | Fri Jan 16 00:00:00 1970 | 5  | 5          | foo
+ 917 |  7 | 00917 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 919 |  9 | 00919 | Tue Jan 20 00:00:00 1970 PST | Tue Jan 20 00:00:00 1970 | 9  | 9          | foo
+ 923 |  3 | 00923 | Sat Jan 24 00:00:00 1970 PST | Sat Jan 24 00:00:00 1970 | 3  | 3          | foo
+ 925 |  5 | 00925 | Mon Jan 26 00:00:00 1970 PST | Mon Jan 26 00:00:00 1970 | 5  | 5          | foo
+(10 rows)
+
+-- EXISTS should be propogated to the highest upper inner join
+EXPLAIN (verbose, costs off)
+	SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                                                      QUERY PLAN                                                                                                                                                                                                                      
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft2 ft2_1)) INNER JOIN (public.ft2 ft2_2)) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r6.c1, r6.c2, r6.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r6 ON (((r1.c2 = r6.c1)) AND ((r1."C 1" > 900)))) INNER JOIN "S 1"."T 1" r8 ON (((r1.c2 = r8.c2)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 3" r9 WHERE ((r1.c2 = r9.c2))) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r7 WHERE ((r7.c2 = r6.c2)))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+ c1 | c2 | c3 | c4 | c5 | c6 | c7 | c8 | c1 | c2 | c3 
+----+----+----+----+----+----+----+----+----+----+----
+(0 rows)
+
 -- ===================================================================
 -- test writable foreign table stuff
 -- ===================================================================
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 50d23f922cc..de08a0e20f2 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -779,6 +779,7 @@ postgresGetForeignRelSize(PlannerInfo *root,
 	fpinfo->make_outerrel_subquery = false;
 	fpinfo->make_innerrel_subquery = false;
 	fpinfo->lower_subquery_rels = NULL;
+	fpinfo->hidden_subquery_rels = NULL;
 	/* Set the relation index. */
 	fpinfo->relation_index = baserel->relid;
 }
@@ -5723,6 +5724,46 @@ postgresImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
 	return commands;
 }
 
+/*
+ * Check if reltarget is safe enough to push down such join.
+ * For semi-join reltarget is not safe, if it contains references
+ * to inner rel relids, which do not belong to outer rel.
+ */
+static bool
+joinrel_target_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype, RelOptInfo *outerrel, RelOptInfo *innerrel)
+{
+	List	   *vars;
+	ListCell   *lc;
+	bool		ok = true;
+
+	Assert(joinrel->reltarget);
+
+	vars = pull_var_clause((Node *) joinrel->reltarget->exprs, PVC_INCLUDE_PLACEHOLDERS);
+
+	foreach(lc, vars)
+	{
+		Var		   *var = (Var *) lfirst(lc);
+
+		if (!IsA(var, Var))
+			continue;
+
+		if (jointype == JOIN_SEMI &&
+			bms_is_member(var->varno, innerrel->relids) &&
+			!bms_is_member(var->varno, outerrel->relids))
+		{
+			/*
+			 * Planner can create semi-joins, which refer to inner rel vars in
+			 * its target list. However, we deparse semi-join as exists()
+			 * subquery, so can't handle references to inner rel in target
+			 * list.
+			 */
+			ok = false;
+			break;
+		}
+	}
+	return ok;
+}
+
 /*
  * Assess whether the join between inner and outer relations can be pushed down
  * to the foreign server. As a side effect, save information we obtain in this
@@ -5740,12 +5781,19 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	List	   *joinclauses;
 
 	/*
-	 * We support pushing down INNER, LEFT, RIGHT and FULL OUTER joins.
-	 * Constructing queries representing SEMI and ANTI joins is hard, hence
-	 * not considered right now.
+	 * We support pushing down INNER, LEFT, RIGHT, FULL OUTER and SEMI joins.
+	 * Constructing queries representing ANTI joins is hard, hence not
+	 * considered right now.
 	 */
 	if (jointype != JOIN_INNER && jointype != JOIN_LEFT &&
-		jointype != JOIN_RIGHT && jointype != JOIN_FULL)
+		jointype != JOIN_RIGHT && jointype != JOIN_FULL &&
+		jointype != JOIN_SEMI)
+		return false;
+
+	/*
+	 * We can't push down join if its reltarget is not safe
+	 */
+	if (!joinrel_target_ok(root, joinrel, jointype, outerrel, innerrel))
 		return false;
 
 	/*
@@ -5857,6 +5905,8 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	Assert(bms_is_subset(fpinfo_i->lower_subquery_rels, innerrel->relids));
 	fpinfo->lower_subquery_rels = bms_union(fpinfo_o->lower_subquery_rels,
 											fpinfo_i->lower_subquery_rels);
+	fpinfo->hidden_subquery_rels = bms_union(fpinfo_o->hidden_subquery_rels,
+											 fpinfo_i->hidden_subquery_rels);
 
 	/*
 	 * Pull the other remote conditions from the joining relations into join
@@ -5900,6 +5950,16 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 											   fpinfo_i->remote_conds);
 			break;
 
+		case JOIN_SEMI:
+			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+											  fpinfo_i->remote_conds);
+			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+											  fpinfo->remote_conds);
+			fpinfo->remote_conds = list_copy(fpinfo_o->remote_conds);
+			fpinfo->hidden_subquery_rels = bms_union(fpinfo->hidden_subquery_rels,
+													 innerrel->relids);
+			break;
+
 		case JOIN_FULL:
 
 			/*
@@ -5942,6 +6002,24 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 		fpinfo->joinclauses = fpinfo->remote_conds;
 		fpinfo->remote_conds = NIL;
 	}
+	else if (jointype == JOIN_LEFT || jointype == JOIN_RIGHT || jointype == JOIN_FULL)
+	{
+		/*
+		 * Conditions, generated from semi-joins, should be evaluated before
+		 * LEFT/RIGHT/FULL join.
+		 */
+		if (!bms_is_empty(fpinfo_o->hidden_subquery_rels))
+		{
+			fpinfo->make_outerrel_subquery = true;
+			fpinfo->lower_subquery_rels = bms_add_members(fpinfo->lower_subquery_rels, outerrel->relids);
+		}
+
+		if (!bms_is_empty(fpinfo_i->hidden_subquery_rels))
+		{
+			fpinfo->make_innerrel_subquery = true;
+			fpinfo->lower_subquery_rels = bms_add_members(fpinfo->lower_subquery_rels, innerrel->relids);
+		}
+	}
 
 	/* Mark that this join can be pushed down safely */
 	fpinfo->pushdown_safe = true;
@@ -7679,6 +7757,8 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 {
 	ListCell   *lc;
 
+	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
+
 	foreach(lc, ec->ec_members)
 	{
 		EquivalenceMember *em = (EquivalenceMember *) lfirst(lc);
@@ -7689,6 +7769,7 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 		 */
 		if (bms_is_subset(em->em_relids, rel->relids) &&
 			!bms_is_empty(em->em_relids) &&
+			bms_is_empty(bms_intersect(em->em_relids, fpinfo->hidden_subquery_rels)) &&
 			is_foreign_expr(root, rel, em->em_expr))
 			return em;
 	}
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index 02c11523199..2b6d54a8fd2 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -118,6 +118,8 @@ typedef struct PgFdwRelationInfo
 										 * subquery? */
 	Relids		lower_subquery_rels;	/* all relids appearing in lower
 										 * subqueries */
+	Relids		hidden_subquery_rels;	/* relids, which can't be referred to
+										 * from upper relations */
 
 	/*
 	 * Index of the relation.  It is used to create an alias to a subquery
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index c37aa803836..e28ea7cd853 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -599,7 +599,7 @@ WITH t (c1_1, c1_3, c2_1) AS MATERIALIZED (SELECT t1.c1, t1.c3, t2.c1 FROM ft1 t
 -- ctid with whole-row reference
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER BY t1.c3, t1.c1 OFFSET 100 LIMIT 10;
--- SEMI JOIN, not pushed down
+-- SEMI JOIN
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
@@ -1274,6 +1274,123 @@ explain (verbose, costs off) select * from ft3 where f2 = 'foo' COLLATE "C";
 explain (verbose, costs off) select * from ft3 f, loct3 l
   where f.f3 = l.f3 COLLATE "POSIX" and l.f1 = 'foo';
 
+-- ===================================================================
+-- test SEMI-JOIN pushdown
+-- ===================================================================
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+
+-- The same query, different join order
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+
+-- Left join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Several semi-joins per upper level join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Semi-join below Semi-join
+EXPLAIN (verbose, costs off)
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Upper level relations shouldn't refer EXISTS() subqueries
+EXPLAIN (verbose, costs off)
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+
+-- EXISTS should be propogated to the highest upper inner join
+EXPLAIN (verbose, costs off)
+	SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+
 -- ===================================================================
 -- test writable foreign table stuff
 -- ===================================================================
-- 
2.34.1

From 91ae85ac735c9f109cd3ab3603693177011e5b94 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <a.pyhalov@postgrespro.ru>
Date: Mon, 7 Nov 2022 10:23:32 +0300
Subject: [PATCH] postgres_fdw: add support for deparsing semi joins

We deparse semi-joins as EXISTS subqueries. So, deparsing
semi-join leads to generating addl_conds condition,
which is then added to the uppermost JOIN's WHERE clause.
---
 contrib/postgres_fdw/deparse.c                | 206 ++++++++---
 .../postgres_fdw/expected/postgres_fdw.out    | 320 ++++++++++++++++--
 contrib/postgres_fdw/postgres_fdw.c           |  94 ++++-
 contrib/postgres_fdw/postgres_fdw.h           |   3 +
 contrib/postgres_fdw/sql/postgres_fdw.sql     | 126 ++++++-
 5 files changed, 668 insertions(+), 81 deletions(-)

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index 09fd489a901..cb0e373055d 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -180,11 +180,14 @@ static void appendConditions(List *exprs, deparse_expr_cxt *context);
 static void deparseFromExprForRel(StringInfo buf, PlannerInfo *root,
 								  RelOptInfo *foreignrel, bool use_alias,
 								  Index ignore_rel, List **ignore_conds,
+								  StringInfo additional_conds,
 								  List **params_list);
+static void appendWhereClause(List *exprs, StringInfo additional_conds, deparse_expr_cxt *context);
 static void deparseFromExpr(List *quals, deparse_expr_cxt *context);
 static void deparseRangeTblRef(StringInfo buf, PlannerInfo *root,
 							   RelOptInfo *foreignrel, bool make_subquery,
-							   Index ignore_rel, List **ignore_conds, List **params_list);
+							   Index ignore_rel, List **ignore_conds,
+							   StringInfo additional_conds, List **params_list);
 static void deparseAggref(Aggref *node, deparse_expr_cxt *context);
 static void appendGroupByClause(List *tlist, deparse_expr_cxt *context);
 static void appendOrderBySuffix(Oid sortop, Oid sortcoltype, bool nulls_first,
@@ -1370,23 +1373,21 @@ deparseFromExpr(List *quals, deparse_expr_cxt *context)
 {
 	StringInfo	buf = context->buf;
 	RelOptInfo *scanrel = context->scanrel;
+	StringInfoData additional_conds;
 
 	/* For upper relations, scanrel must be either a joinrel or a baserel */
 	Assert(!IS_UPPER_REL(context->foreignrel) ||
 		   IS_JOIN_REL(scanrel) || IS_SIMPLE_REL(scanrel));
 
+	initStringInfo(&additional_conds);
 	/* Construct FROM clause */
 	appendStringInfoString(buf, " FROM ");
 	deparseFromExprForRel(buf, context->root, scanrel,
 						  (bms_membership(scanrel->relids) == BMS_MULTIPLE),
-						  (Index) 0, NULL, context->params_list);
-
-	/* Construct WHERE clause */
-	if (quals != NIL)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(quals, context);
-	}
+						  (Index) 0, NULL, &additional_conds,
+						  context->params_list);
+	appendWhereClause(quals, &additional_conds, context);
+	pfree(additional_conds.data);
 }
 
 /*
@@ -1598,6 +1599,33 @@ appendConditions(List *exprs, deparse_expr_cxt *context)
 	reset_transmission_modes(nestlevel);
 }
 
+/*
+ * Append WHERE clause, containing conditions
+ * from exprs and additional_conds, to context->buf.
+ */
+static void
+appendWhereClause(List *exprs, StringInfo additional_conds, deparse_expr_cxt *context)
+{
+	StringInfo	buf = context->buf;
+	bool		need_and = false;
+
+	if (exprs != NIL || additional_conds->len > 0)
+		appendStringInfoString(buf, " WHERE ");
+
+	if (exprs != NIL)
+	{
+		appendConditions(exprs, context);
+		need_and = true;
+	}
+
+	if (additional_conds->len > 0)
+	{
+		if (need_and)
+			appendStringInfoString(buf, " AND ");
+		appendStringInfo(buf, "(%s)", additional_conds->data);
+	}
+}
+
 /* Output join name for given join type */
 const char *
 get_jointype_name(JoinType jointype)
@@ -1616,6 +1644,9 @@ get_jointype_name(JoinType jointype)
 		case JOIN_FULL:
 			return "FULL";
 
+		case JOIN_SEMI:
+			return "SEMI";
+
 		default:
 			/* Shouldn't come here, but protect from buggy code. */
 			elog(ERROR, "unsupported join type %d", jointype);
@@ -1712,11 +1743,14 @@ deparseSubqueryTargetList(deparse_expr_cxt *context)
  * of DELETE; it deparses the join relation as if the relation never contained
  * the target relation, and creates a List of conditions to be deparsed into
  * the top-level WHERE clause, which is returned to *ignore_conds.
+ *
+ * 'additional_conds' is a initialized StringInfo. If some additional conditions
+ * should be appended to WHERE clause, they are returned as additional_conds.
  */
 static void
 deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 					  bool use_alias, Index ignore_rel, List **ignore_conds,
-					  List **params_list)
+					  StringInfo additional_conds, List **params_list)
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
@@ -1728,6 +1762,9 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		RelOptInfo *innerrel = fpinfo->innerrel;
 		bool		outerrel_is_target = false;
 		bool		innerrel_is_target = false;
+		StringInfoData additional_conds_i;
+		StringInfoData additional_conds_o;
+		bool		need_and;
 
 		if (ignore_rel > 0 && bms_is_member(ignore_rel, foreignrel->relids))
 		{
@@ -1761,10 +1798,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		/* Deparse outer relation if not the target relation. */
 		if (!outerrel_is_target)
 		{
+			initStringInfo(&additional_conds_o);
 			initStringInfo(&join_sql_o);
 			deparseRangeTblRef(&join_sql_o, root, outerrel,
 							   fpinfo->make_outerrel_subquery,
-							   ignore_rel, ignore_conds, params_list);
+							   ignore_rel, ignore_conds, &additional_conds_o,
+							   params_list);
 
 			/*
 			 * If inner relation is the target relation, skip deparsing it.
@@ -1780,6 +1819,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				Assert(fpinfo->jointype == JOIN_INNER);
 				Assert(fpinfo->joinclauses == NIL);
 				appendBinaryStringInfo(buf, join_sql_o.data, join_sql_o.len);
+				if (additional_conds_o.len > 0)
+				{
+					Assert(additional_conds->len == 0);
+					appendStringInfoString(additional_conds, additional_conds_o.data);
+				}
+				pfree(additional_conds_o.data);
 				return;
 			}
 		}
@@ -1787,10 +1832,35 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		/* Deparse inner relation if not the target relation. */
 		if (!innerrel_is_target)
 		{
+			initStringInfo(&additional_conds_i);
+
 			initStringInfo(&join_sql_i);
 			deparseRangeTblRef(&join_sql_i, root, innerrel,
 							   fpinfo->make_innerrel_subquery,
-							   ignore_rel, ignore_conds, params_list);
+							   ignore_rel, ignore_conds, &additional_conds_i,
+							   params_list);
+
+			if (fpinfo->jointype == JOIN_SEMI)
+			{
+				deparse_expr_cxt context;
+
+				appendStringInfo(additional_conds, "EXISTS (SELECT NULL FROM %s",
+								 join_sql_i.data);
+
+				context.buf = additional_conds;
+				context.foreignrel = foreignrel;
+				context.scanrel = foreignrel;
+				context.root = root;
+				context.params_list = params_list;
+
+				appendWhereClause(fpinfo->joinclauses, &additional_conds_i, &context);
+
+				if (additional_conds_i.len > 0)
+					resetStringInfo(&additional_conds_i);
+
+				/* Close parentheses for EXISTS subquery */
+				appendStringInfo(additional_conds, ")");
+			}
 
 			/*
 			 * If outer relation is the target relation, skip deparsing it.
@@ -1801,6 +1871,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				Assert(fpinfo->jointype == JOIN_INNER);
 				Assert(fpinfo->joinclauses == NIL);
 				appendBinaryStringInfo(buf, join_sql_i.data, join_sql_i.len);
+				if (additional_conds_i.len > 0)
+				{
+					Assert(additional_conds->len == 0);
+					appendStringInfoString(additional_conds, additional_conds_i.data);
+				}
+				pfree(additional_conds_i.data);
 				return;
 			}
 		}
@@ -1809,33 +1885,69 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		Assert(!outerrel_is_target && !innerrel_is_target);
 
 		/*
-		 * For a join relation FROM clause entry is deparsed as
-		 *
-		 * ((outer relation) <join type> (inner relation) ON (joinclauses))
+		 * For semijoin FROM clause is deparsed as an outer relation. An inner
+		 * relation and join clauses are converted to EXISTS condition and
+		 * passed to the upper level.
 		 */
-		appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
-						 get_jointype_name(fpinfo->jointype), join_sql_i.data);
-
-		/* Append join clause; (TRUE) if no join clause */
-		if (fpinfo->joinclauses)
+		if (fpinfo->jointype == JOIN_SEMI)
 		{
-			deparse_expr_cxt context;
+			appendStringInfo(buf, "%s", join_sql_o.data);
+		}
+		else
+		{
+			/*
+			 * For a join relation FROM clause entry is deparsed as
+			 *
+			 * ((outer relation) <join type> (inner relation) ON
+			 * (joinclauses))
+			 */
+			appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
+							 get_jointype_name(fpinfo->jointype), join_sql_i.data);
+
+			/* Append join clause; (TRUE) if no join clause */
+			if (fpinfo->joinclauses)
+			{
+				deparse_expr_cxt context;
 
-			context.buf = buf;
-			context.foreignrel = foreignrel;
-			context.scanrel = foreignrel;
-			context.root = root;
-			context.params_list = params_list;
+				context.buf = buf;
+				context.foreignrel = foreignrel;
+				context.scanrel = foreignrel;
+				context.root = root;
+				context.params_list = params_list;
 
-			appendStringInfoChar(buf, '(');
-			appendConditions(fpinfo->joinclauses, &context);
+				appendStringInfoChar(buf, '(');
+				appendConditions(fpinfo->joinclauses, &context);
+				appendStringInfoChar(buf, ')');
+			}
+			else
+				appendStringInfoString(buf, "(TRUE)");
+
+			/* End the FROM clause entry. */
 			appendStringInfoChar(buf, ')');
 		}
-		else
-			appendStringInfoString(buf, "(TRUE)");
 
-		/* End the FROM clause entry. */
-		appendStringInfoChar(buf, ')');
+		/*
+		 * Construct additional_conds from current level additional_conds and
+		 * additional_conds, coming from inner and outer rels.
+		 */
+		need_and = false;
+		if (additional_conds->len > 0)
+			need_and = true;
+		if (additional_conds_o.len > 0)
+		{
+			if (need_and)
+				appendStringInfoString(additional_conds, " AND ");
+			appendStringInfoString(additional_conds, additional_conds_o.data);
+			need_and = true;
+		}
+		if (additional_conds_i.len > 0)
+		{
+			if (need_and)
+				appendStringInfoString(additional_conds, " AND ");
+			appendStringInfoString(additional_conds, additional_conds_i.data);
+		}
+		pfree(additional_conds_i.data);
+		pfree(additional_conds_o.data);
 	}
 	else
 	{
@@ -1867,7 +1979,7 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 static void
 deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				   bool make_subquery, Index ignore_rel, List **ignore_conds,
-				   List **params_list)
+				   StringInfo additional_conds, List **params_list)
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
@@ -1925,7 +2037,8 @@ deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 	}
 	else
 		deparseFromExprForRel(buf, root, foreignrel, true, ignore_rel,
-							  ignore_conds, params_list);
+							  ignore_conds, additional_conds,
+							  params_list);
 }
 
 /*
@@ -2148,6 +2261,7 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 	RangeTblEntry *rte = planner_rt_fetch(rtindex, root);
 	ListCell   *lc,
 			   *lc2;
+	StringInfoData additional_conds;
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -2185,21 +2299,21 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 
 	reset_transmission_modes(nestlevel);
 
+	initStringInfo(&additional_conds);
+
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 	{
 		List	   *ignore_conds = NIL;
 
+
 		appendStringInfoString(buf, " FROM ");
 		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
-							  &ignore_conds, params_list);
+							  &ignore_conds, &additional_conds, params_list);
 		remote_conds = list_concat(remote_conds, ignore_conds);
 	}
 
-	if (remote_conds)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(remote_conds, &context);
-	}
+	appendWhereClause(remote_conds, &additional_conds, &context);
+	pfree(additional_conds.data);
 
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		deparseExplicitTargetList(returningList, true, retrieved_attrs,
@@ -2255,6 +2369,7 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 					   List **retrieved_attrs)
 {
 	deparse_expr_cxt context;
+	StringInfoData additional_conds;
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -2268,21 +2383,20 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		appendStringInfo(buf, " %s%d", REL_ALIAS_PREFIX, rtindex);
 
+	initStringInfo(&additional_conds);
+
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 	{
 		List	   *ignore_conds = NIL;
 
 		appendStringInfoString(buf, " USING ");
 		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
-							  &ignore_conds, params_list);
+							  &ignore_conds, &additional_conds, params_list);
 		remote_conds = list_concat(remote_conds, ignore_conds);
 	}
 
-	if (remote_conds)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(remote_conds, &context);
-	}
+	appendWhereClause(remote_conds, &additional_conds, &context);
+	pfree(additional_conds.data);
 
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		deparseExplicitTargetList(returningList, true, retrieved_attrs,
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 144c114d0fe..14579030fab 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -2001,23 +2001,16 @@ SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER B
    Remote SQL: SELECT r1.ctid, CASE WHEN (r1.*)::text IS NOT NULL THEN ROW(r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8) END, CASE WHEN (r2.*)::text IS NOT NULL THEN ROW(r2."C 1", r2.c2, r2.c3, r2.c4, r2.c5, r2.c6, r2.c7, r2.c8) END, r1."C 1", r1.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r2."C 1" = r1."C 1")))) ORDER BY r1.c3 ASC NULLS LAST, r1."C 1" ASC NULLS LAST LIMIT 10::bigint OFFSET 100::bigint
 (4 rows)
 
--- SEMI JOIN, not pushed down
+-- SEMI JOIN
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
-                                      QUERY PLAN                                       
----------------------------------------------------------------------------------------
- Limit
+                                                                                              QUERY PLAN                                                                                               
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
    Output: t1.c1
-   ->  Merge Semi Join
-         Output: t1.c1
-         Merge Cond: (t1.c1 = t2.c1)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1
-               Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-         ->  Foreign Scan on public.ft2 t2
-               Output: t2.c1
-               Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-(11 rows)
+   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
+   Remote SQL: SELECT r1."C 1" FROM "S 1"."T 1" r1 WHERE (EXISTS (SELECT NULL FROM "S 1"."T 1" r2 WHERE ((r2."C 1" = r1."C 1")))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint OFFSET 100::bigint
+(4 rows)
 
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
  c1  
@@ -4055,23 +4048,13 @@ EXECUTE st2(101, 121);
 -- subquery using immutable function (can be sent to remote)
 PREPARE st3(int) AS SELECT * FROM ft1 t1 WHERE t1.c1 < $2 AND t1.c3 IN (SELECT c3 FROM ft2 t2 WHERE c1 > $1 AND date(c5) = '1970-01-17'::date) ORDER BY c1;
 EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st3(10, 20);
-                                                      QUERY PLAN                                                       
------------------------------------------------------------------------------------------------------------------------
- Sort
+                                                                                                                                            QUERY PLAN                                                                                                                                             
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
    Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-   Sort Key: t1.c1
-   ->  Nested Loop Semi Join
-         Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-         Join Filter: (t2.c3 = t1.c3)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-               Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" WHERE (("C 1" < 20))
-         ->  Materialize
-               Output: t2.c3
-               ->  Foreign Scan on public.ft2 t2
-                     Output: t2.c3
-                     Remote SQL: SELECT c3 FROM "S 1"."T 1" WHERE (("C 1" > 10)) AND ((date(c5) = '1970-01-17'::date))
-(14 rows)
+   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" < 20)) AND (EXISTS (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r3."C 1" > 10)) AND ((date(r3.c5) = '1970-01-17'::date)) AND ((r3.c3 = r1.c3)))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
 
 EXECUTE st3(10, 20);
  c1 | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
@@ -4615,6 +4598,283 @@ explain (verbose, costs off) select * from ft3 f, loct3 l
                Index Cond: (l.f1 = 'foo'::text)
 (12 rows)
 
+-- ===================================================================
+-- test SEMI-JOIN pushdown
+-- ===================================================================
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+                                                                                                                                                 QUERY PLAN                                                                                                                                                  
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r2.c1, r2.c2, r2.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r2 ON (((r1.c2 = r2.c1)) AND ((r1."C 1" > 900)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 4" r4 WHERE ((r1.c2 = r4.c1)))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 916 |  6 | 00916 | Sat Jan 17 00:00:00 1970 PST | Sat Jan 17 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 926 |  6 | 00926 | Tue Jan 27 00:00:00 1970 PST | Tue Jan 27 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 936 |  6 | 00936 | Fri Feb 06 00:00:00 1970 PST | Fri Feb 06 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 946 |  6 | 00946 | Mon Feb 16 00:00:00 1970 PST | Mon Feb 16 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 956 |  6 | 00956 | Thu Feb 26 00:00:00 1970 PST | Thu Feb 26 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 966 |  6 | 00966 | Sun Mar 08 00:00:00 1970 PST | Sun Mar 08 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 976 |  6 | 00976 | Wed Mar 18 00:00:00 1970 PST | Wed Mar 18 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 986 |  6 | 00986 | Sat Mar 28 00:00:00 1970 PST | Sat Mar 28 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 996 |  6 | 00996 | Tue Apr 07 00:00:00 1970 PST | Tue Apr 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- The same query, different join order
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+                                                                                                                                                 QUERY PLAN                                                                                                                                                  
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r4.c1, r4.c2, r4.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r4 ON (((r1.c2 = r4.c1)) AND ((r1."C 1" > 900)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 4" r5 WHERE ((r4.c1 = r5.c1)))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 916 |  6 | 00916 | Sat Jan 17 00:00:00 1970 PST | Sat Jan 17 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 926 |  6 | 00926 | Tue Jan 27 00:00:00 1970 PST | Tue Jan 27 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 936 |  6 | 00936 | Fri Feb 06 00:00:00 1970 PST | Fri Feb 06 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 946 |  6 | 00946 | Mon Feb 16 00:00:00 1970 PST | Mon Feb 16 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 956 |  6 | 00956 | Thu Feb 26 00:00:00 1970 PST | Thu Feb 26 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 966 |  6 | 00966 | Sun Mar 08 00:00:00 1970 PST | Sun Mar 08 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 976 |  6 | 00976 | Wed Mar 18 00:00:00 1970 PST | Wed Mar 18 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 986 |  6 | 00986 | Sat Mar 28 00:00:00 1970 PST | Sat Mar 28 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 996 |  6 | 00996 | Tue Apr 07 00:00:00 1970 PST | Tue Apr 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- Left join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                   QUERY PLAN                                                                                                                                                                                   
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: (public.ft2) LEFT JOIN ((public.ft4) SEMI JOIN (public.ft5))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, s6.c1, s6.c2, s6.c3 FROM ("S 1"."T 1" r1 LEFT JOIN (SELECT r4.c1, r4.c2, r4.c3 FROM "S 1"."T 3" r4 WHERE (EXISTS (SELECT NULL FROM "S 1"."T 4" r5 WHERE ((r4.c1 = r5.c1))))) s6(c1, c2, c3) ON (((r1.c2 = s6.c1)))) WHERE ((r1."C 1" > 900)) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 901 |  1 | 00901 | Fri Jan 02 00:00:00 1970 PST | Fri Jan 02 00:00:00 1970 | 1  | 1          | foo |    |    | 
+ 902 |  2 | 00902 | Sat Jan 03 00:00:00 1970 PST | Sat Jan 03 00:00:00 1970 | 2  | 2          | foo |    |    | 
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo |    |    | 
+ 904 |  4 | 00904 | Mon Jan 05 00:00:00 1970 PST | Mon Jan 05 00:00:00 1970 | 4  | 4          | foo |    |    | 
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo |    |    | 
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo |    |    | 
+ 908 |  8 | 00908 | Fri Jan 09 00:00:00 1970 PST | Fri Jan 09 00:00:00 1970 | 8  | 8          | foo |    |    | 
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo |    |    | 
+ 910 |  0 | 00910 | Sun Jan 11 00:00:00 1970 PST | Sun Jan 11 00:00:00 1970 | 0  | 0          | foo |    |    | 
+(10 rows)
+
+-- Several semi-joins per upper level join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                                                      QUERY PLAN                                                                                                                                                                                                                       
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)) INNER JOIN (public.ft5 ft5_1)) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r6.c1, r6.c2, r6.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r6 ON (((r1.c2 = r6.c1)) AND ((r1."C 1" > 900)))) INNER JOIN "S 1"."T 4" r8 ON (((r1.c2 <= r8.c1)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 3" r9 WHERE ((r8.c1 = r9.c1))) AND EXISTS (SELECT NULL FROM "S 1"."T 4" r7 WHERE ((r6.c1 = r7.c1)))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- Semi-join below Semi-join
+EXPLAIN (verbose, costs off)
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                            QUERY PLAN                                                                                                                                                             
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8
+   Relations: (public.ft2) SEMI JOIN ((public.ft2 ft2_1) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" > 900)) AND (EXISTS (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r1."C 1" = r3."C 1")) AND (EXISTS (SELECT NULL FROM "S 1"."T 3" r4 WHERE ((r3.c2 = r4.c2)))))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
+-----+----+-------+------------------------------+--------------------------+----+------------+-----
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo
+ 913 |  3 | 00913 | Wed Jan 14 00:00:00 1970 PST | Wed Jan 14 00:00:00 1970 | 3  | 3          | foo
+ 915 |  5 | 00915 | Fri Jan 16 00:00:00 1970 PST | Fri Jan 16 00:00:00 1970 | 5  | 5          | foo
+ 917 |  7 | 00917 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 919 |  9 | 00919 | Tue Jan 20 00:00:00 1970 PST | Tue Jan 20 00:00:00 1970 | 9  | 9          | foo
+ 923 |  3 | 00923 | Sat Jan 24 00:00:00 1970 PST | Sat Jan 24 00:00:00 1970 | 3  | 3          | foo
+ 925 |  5 | 00925 | Mon Jan 26 00:00:00 1970 PST | Mon Jan 26 00:00:00 1970 | 5  | 5          | foo
+(10 rows)
+
+-- Upper level relations shouldn't refer EXISTS() subqueries
+EXPLAIN (verbose, costs off)
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+                                                                                                                                                            QUERY PLAN                                                                                                                                                             
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ftupper.c1, ftupper.c2, ftupper.c3, ftupper.c4, ftupper.c5, ftupper.c6, ftupper.c7, ftupper.c8
+   Relations: (public.ft2 ftupper) SEMI JOIN ((public.ft2) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" > 900)) AND (EXISTS (SELECT NULL FROM "S 1"."T 1" r2 WHERE ((r1."C 1" = r2."C 1")) AND (EXISTS (SELECT NULL FROM "S 1"."T 3" r3 WHERE ((r2.c2 = r3.c2)))))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
+-----+----+-------+------------------------------+--------------------------+----+------------+-----
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo
+ 913 |  3 | 00913 | Wed Jan 14 00:00:00 1970 PST | Wed Jan 14 00:00:00 1970 | 3  | 3          | foo
+ 915 |  5 | 00915 | Fri Jan 16 00:00:00 1970 PST | Fri Jan 16 00:00:00 1970 | 5  | 5          | foo
+ 917 |  7 | 00917 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 919 |  9 | 00919 | Tue Jan 20 00:00:00 1970 PST | Tue Jan 20 00:00:00 1970 | 9  | 9          | foo
+ 923 |  3 | 00923 | Sat Jan 24 00:00:00 1970 PST | Sat Jan 24 00:00:00 1970 | 3  | 3          | foo
+ 925 |  5 | 00925 | Mon Jan 26 00:00:00 1970 PST | Mon Jan 26 00:00:00 1970 | 5  | 5          | foo
+(10 rows)
+
+-- EXISTS should be propogated to the highest upper inner join
+EXPLAIN (verbose, costs off)
+	SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                                                      QUERY PLAN                                                                                                                                                                                                                      
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft2 ft2_1)) INNER JOIN (public.ft2 ft2_2)) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r6.c1, r6.c2, r6.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r6 ON (((r1.c2 = r6.c1)) AND ((r1."C 1" > 900)))) INNER JOIN "S 1"."T 1" r8 ON (((r1.c2 = r8.c2)))) WHERE (EXISTS (SELECT NULL FROM "S 1"."T 3" r9 WHERE ((r1.c2 = r9.c2))) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r7 WHERE ((r7.c2 = r6.c2)))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+ c1 | c2 | c3 | c4 | c5 | c6 | c7 | c8 | c1 | c2 | c3 
+----+----+----+----+----+----+----+----+----+----+----
+(0 rows)
+
+-- Can't push down semi-join with inner rel vars in targetlist
+EXPLAIN (verbose, costs off)
+SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
+	ft1.c1 IN (
+		SELECT ft2.c1 FROM ft2 JOIN ft4 ON ft2.c1 = ft4.c1)
+	ORDER BY ft1.c1 LIMIT 5;
+                                                                            QUERY PLAN                                                                             
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Limit
+   Output: ft1.c1
+   ->  Merge Semi Join
+         Output: ft1.c1
+         Merge Cond: (ft1.c1 = ft2_1.c1)
+         ->  Foreign Scan
+               Output: ft1.c1, ft2.c1
+               Relations: (public.ft1) INNER JOIN (public.ft2)
+               Remote SQL: SELECT r1."C 1", r2."C 1" FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r2."C 1" = r1."C 1")))) ORDER BY r1."C 1" ASC NULLS LAST
+         ->  Foreign Scan
+               Output: ft2_1.c1, ft4.c1
+               Relations: (public.ft2 ft2_1) INNER JOIN (public.ft4)
+               Remote SQL: SELECT r5."C 1", r6.c1 FROM ("S 1"."T 1" r5 INNER JOIN "S 1"."T 3" r6 ON (((r5."C 1" = r6.c1)))) ORDER BY r5."C 1" ASC NULLS LAST
+(13 rows)
+
 -- ===================================================================
 -- test writable foreign table stuff
 -- ===================================================================
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 8b3206ceaa3..f718798ff7c 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -779,6 +779,7 @@ postgresGetForeignRelSize(PlannerInfo *root,
 	fpinfo->make_outerrel_subquery = false;
 	fpinfo->make_innerrel_subquery = false;
 	fpinfo->lower_subquery_rels = NULL;
+	fpinfo->hidden_subquery_rels = NULL;
 	/* Set the relation index. */
 	fpinfo->relation_index = baserel->relid;
 }
@@ -5724,6 +5725,45 @@ postgresImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
 	return commands;
 }
 
+/*
+ * Check if reltarget is safe enough to push down semi-join.
+ * Reltarget is not safe, if it contains references
+ * to inner rel relids, which do not belong to outer rel.
+ */
+static bool
+semijoin_target_ok(PlannerInfo *root, RelOptInfo *joinrel, RelOptInfo *outerrel, RelOptInfo *innerrel)
+{
+	List	   *vars;
+	ListCell   *lc;
+	bool		ok = true;
+
+	Assert(joinrel->reltarget);
+
+	vars = pull_var_clause((Node *) joinrel->reltarget->exprs, PVC_INCLUDE_PLACEHOLDERS);
+
+	foreach(lc, vars)
+	{
+		Var		   *var = (Var *) lfirst(lc);
+
+		if (!IsA(var, Var))
+			continue;
+
+		if (bms_is_member(var->varno, innerrel->relids) &&
+			!bms_is_member(var->varno, outerrel->relids))
+		{
+			/*
+			 * Planner can create semi-joins, which refer to inner rel vars in
+			 * its target list. However, we deparse semi-join as exists()
+			 * subquery, so can't handle references to inner rel in target
+			 * list.
+			 */
+			ok = false;
+			break;
+		}
+	}
+	return ok;
+}
+
 /*
  * Assess whether the join between inner and outer relations can be pushed down
  * to the foreign server. As a side effect, save information we obtain in this
@@ -5741,12 +5781,19 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	List	   *joinclauses;
 
 	/*
-	 * We support pushing down INNER, LEFT, RIGHT and FULL OUTER joins.
-	 * Constructing queries representing SEMI and ANTI joins is hard, hence
-	 * not considered right now.
+	 * We support pushing down INNER, LEFT, RIGHT, FULL OUTER and SEMI joins.
+	 * Constructing queries representing ANTI joins is hard, hence not
+	 * considered right now.
 	 */
 	if (jointype != JOIN_INNER && jointype != JOIN_LEFT &&
-		jointype != JOIN_RIGHT && jointype != JOIN_FULL)
+		jointype != JOIN_RIGHT && jointype != JOIN_FULL &&
+		jointype != JOIN_SEMI)
+		return false;
+
+	/*
+	 * We can't push down semi-join if its reltarget is not safe
+	 */
+	if ((jointype == JOIN_SEMI) && !semijoin_target_ok(root, joinrel, outerrel, innerrel))
 		return false;
 
 	/*
@@ -5858,6 +5905,8 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	Assert(bms_is_subset(fpinfo_i->lower_subquery_rels, innerrel->relids));
 	fpinfo->lower_subquery_rels = bms_union(fpinfo_o->lower_subquery_rels,
 											fpinfo_i->lower_subquery_rels);
+	fpinfo->hidden_subquery_rels = bms_union(fpinfo_o->hidden_subquery_rels,
+											 fpinfo_i->hidden_subquery_rels);
 
 	/*
 	 * Pull the other remote conditions from the joining relations into join
@@ -5871,6 +5920,12 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	 * the joinclauses, since they need to be evaluated while constructing the
 	 * join.
 	 *
+	 * For SEMI-JOIN clauses from inner relation can not be added to remote_conds,
+	 * but should be treated as join clauses (as they are deparsed to EXISTS
+	 * subquery, where inner relation can be referred). A list of relation ids,
+	 * which can't be referred from higher levels, is preserved as
+	 * hidden_subquery_rels list.
+	 *
 	 * For a FULL OUTER JOIN, the other clauses from either relation can not
 	 * be added to the joinclauses or remote_conds, since each relation acts
 	 * as an outer relation for the other.
@@ -5901,6 +5956,16 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 											   fpinfo_i->remote_conds);
 			break;
 
+		case JOIN_SEMI:
+			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+											  fpinfo_i->remote_conds);
+			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+											  fpinfo->remote_conds);
+			fpinfo->remote_conds = list_copy(fpinfo_o->remote_conds);
+			fpinfo->hidden_subquery_rels = bms_union(fpinfo->hidden_subquery_rels,
+													 innerrel->relids);
+			break;
+
 		case JOIN_FULL:
 
 			/*
@@ -5943,6 +6008,24 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 		fpinfo->joinclauses = fpinfo->remote_conds;
 		fpinfo->remote_conds = NIL;
 	}
+	else if (jointype == JOIN_LEFT || jointype == JOIN_RIGHT || jointype == JOIN_FULL)
+	{
+		/*
+		 * Conditions, generated from semi-joins, should be evaluated before
+		 * LEFT/RIGHT/FULL join.
+		 */
+		if (!bms_is_empty(fpinfo_o->hidden_subquery_rels))
+		{
+			fpinfo->make_outerrel_subquery = true;
+			fpinfo->lower_subquery_rels = bms_add_members(fpinfo->lower_subquery_rels, outerrel->relids);
+		}
+
+		if (!bms_is_empty(fpinfo_i->hidden_subquery_rels))
+		{
+			fpinfo->make_innerrel_subquery = true;
+			fpinfo->lower_subquery_rels = bms_add_members(fpinfo->lower_subquery_rels, innerrel->relids);
+		}
+	}
 
 	/* Mark that this join can be pushed down safely */
 	fpinfo->pushdown_safe = true;
@@ -7692,6 +7775,8 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 {
 	ListCell   *lc;
 
+	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
+
 	foreach(lc, ec->ec_members)
 	{
 		EquivalenceMember *em = (EquivalenceMember *) lfirst(lc);
@@ -7702,6 +7787,7 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 		 */
 		if (bms_is_subset(em->em_relids, rel->relids) &&
 			!bms_is_empty(em->em_relids) &&
+			bms_is_empty(bms_intersect(em->em_relids, fpinfo->hidden_subquery_rels)) &&
 			is_foreign_expr(root, rel, em->em_expr))
 			return em;
 	}
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index 47157ac887e..1881292ce98 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -118,6 +118,9 @@ typedef struct PgFdwRelationInfo
 										 * subquery? */
 	Relids		lower_subquery_rels;	/* all relids appearing in lower
 										 * subqueries */
+	Relids		hidden_subquery_rels;	/* relids, which can't be referred to
+										 * from upper relations,
+										 * used internally for em search */
 
 	/*
 	 * Index of the relation.  It is used to create an alias to a subquery
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index a303bfb322d..76ba154cbc3 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -600,7 +600,7 @@ WITH t (c1_1, c1_3, c2_1) AS MATERIALIZED (SELECT t1.c1, t1.c3, t2.c1 FROM ft1 t
 -- ctid with whole-row reference
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER BY t1.c3, t1.c1 OFFSET 100 LIMIT 10;
--- SEMI JOIN, not pushed down
+-- SEMI JOIN
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
@@ -1301,6 +1301,130 @@ explain (verbose, costs off) select * from ft3 where f2 = 'foo' COLLATE "C";
 explain (verbose, costs off) select * from ft3 f, loct3 l
   where f.f3 = l.f3 COLLATE "POSIX" and l.f1 = 'foo';
 
+-- ===================================================================
+-- test SEMI-JOIN pushdown
+-- ===================================================================
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+
+-- The same query, different join order
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+
+-- Left join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Several semi-joins per upper level join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Semi-join below Semi-join
+EXPLAIN (verbose, costs off)
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Upper level relations shouldn't refer EXISTS() subqueries
+EXPLAIN (verbose, costs off)
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+
+-- EXISTS should be propogated to the highest upper inner join
+EXPLAIN (verbose, costs off)
+	SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+
+-- Can't push down semi-join with inner rel vars in targetlist
+EXPLAIN (verbose, costs off)
+SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
+	ft1.c1 IN (
+		SELECT ft2.c1 FROM ft2 JOIN ft4 ON ft2.c1 = ft4.c1)
+	ORDER BY ft1.c1 LIMIT 5;
+
 -- ===================================================================
 -- test writable foreign table stuff
 -- ===================================================================
-- 
2.34.1

From 77add3c5532b3505eafd886e28d5101c13f4c81f Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <a.pyhalov@postgrespro.ru>
Date: Mon, 7 Nov 2022 10:23:32 +0300
Subject: [PATCH] postgres_fdw: add support for deparsing semi joins

We deparse semi-joins as EXISTS subqueries. So, deparsing
semi-join leads to generating addl_conds condition,
which is then added to the uppermost JOIN's WHERE clause.
---
 contrib/postgres_fdw/deparse.c                | 205 ++++++++---
 .../postgres_fdw/expected/postgres_fdw.out    | 320 ++++++++++++++++--
 contrib/postgres_fdw/postgres_fdw.c           |  94 ++++-
 contrib/postgres_fdw/postgres_fdw.h           |   3 +
 contrib/postgres_fdw/sql/postgres_fdw.sql     | 126 ++++++-
 5 files changed, 667 insertions(+), 81 deletions(-)

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index 09fd489a901..408d80d235c 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -180,11 +180,15 @@ static void appendConditions(List *exprs, deparse_expr_cxt *context);
 static void deparseFromExprForRel(StringInfo buf, PlannerInfo *root,
 								  RelOptInfo *foreignrel, bool use_alias,
 								  Index ignore_rel, List **ignore_conds,
+								  List **additional_conds,
 								  List **params_list);
+static void appendWhereClause(List *exprs, List *additional_conds,
+							  deparse_expr_cxt *context);
 static void deparseFromExpr(List *quals, deparse_expr_cxt *context);
 static void deparseRangeTblRef(StringInfo buf, PlannerInfo *root,
 							   RelOptInfo *foreignrel, bool make_subquery,
-							   Index ignore_rel, List **ignore_conds, List **params_list);
+							   Index ignore_rel, List **ignore_conds,
+							   List **additional_conds, List **params_list);
 static void deparseAggref(Aggref *node, deparse_expr_cxt *context);
 static void appendGroupByClause(List *tlist, deparse_expr_cxt *context);
 static void appendOrderBySuffix(Oid sortop, Oid sortcoltype, bool nulls_first,
@@ -1370,6 +1374,7 @@ deparseFromExpr(List *quals, deparse_expr_cxt *context)
 {
 	StringInfo	buf = context->buf;
 	RelOptInfo *scanrel = context->scanrel;
+	List	   *additional_conds = NIL;
 
 	/* For upper relations, scanrel must be either a joinrel or a baserel */
 	Assert(!IS_UPPER_REL(context->foreignrel) ||
@@ -1379,14 +1384,11 @@ deparseFromExpr(List *quals, deparse_expr_cxt *context)
 	appendStringInfoString(buf, " FROM ");
 	deparseFromExprForRel(buf, context->root, scanrel,
 						  (bms_membership(scanrel->relids) == BMS_MULTIPLE),
-						  (Index) 0, NULL, context->params_list);
-
-	/* Construct WHERE clause */
-	if (quals != NIL)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(quals, context);
-	}
+						  (Index) 0, NULL, &additional_conds,
+						  context->params_list);
+	appendWhereClause(quals, additional_conds, context);
+	if (additional_conds != NIL)
+		list_free_deep(additional_conds);
 }
 
 /*
@@ -1598,6 +1600,35 @@ appendConditions(List *exprs, deparse_expr_cxt *context)
 	reset_transmission_modes(nestlevel);
 }
 
+/*
+ * Append WHERE clause, containing conditions
+ * from exprs and additional_conds, to context->buf.
+ */
+static void
+appendWhereClause(List *exprs, List *additional_conds, deparse_expr_cxt *context)
+{
+	StringInfo	buf = context->buf;
+	bool		need_and = false;
+	ListCell   *lc;
+
+	if (exprs != NIL || additional_conds != NIL)
+		appendStringInfoString(buf, " WHERE ");
+
+	if (exprs != NIL)
+	{
+		appendConditions(exprs, context);
+		need_and = true;
+	}
+
+	foreach(lc, additional_conds)
+	{
+		if (need_and)
+			appendStringInfoString(buf, " AND ");
+		appendStringInfoString(buf, (char *) lc->ptr_value);
+		need_and = true;
+	}
+}
+
 /* Output join name for given join type */
 const char *
 get_jointype_name(JoinType jointype)
@@ -1616,6 +1647,9 @@ get_jointype_name(JoinType jointype)
 		case JOIN_FULL:
 			return "FULL";
 
+		case JOIN_SEMI:
+			return "SEMI";
+
 		default:
 			/* Shouldn't come here, but protect from buggy code. */
 			elog(ERROR, "unsupported join type %d", jointype);
@@ -1712,11 +1746,14 @@ deparseSubqueryTargetList(deparse_expr_cxt *context)
  * of DELETE; it deparses the join relation as if the relation never contained
  * the target relation, and creates a List of conditions to be deparsed into
  * the top-level WHERE clause, which is returned to *ignore_conds.
+ *
+ * 'additional_conds' is a pointer to list of strings to be appended to WHERE
+ * clause.
  */
 static void
 deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 					  bool use_alias, Index ignore_rel, List **ignore_conds,
-					  List **params_list)
+					  List **additional_conds, List **params_list)
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
@@ -1728,6 +1765,8 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		RelOptInfo *innerrel = fpinfo->innerrel;
 		bool		outerrel_is_target = false;
 		bool		innerrel_is_target = false;
+		List	   *additional_conds_i = NIL;
+		List	   *additional_conds_o = NIL;
 
 		if (ignore_rel > 0 && bms_is_member(ignore_rel, foreignrel->relids))
 		{
@@ -1764,7 +1803,8 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 			initStringInfo(&join_sql_o);
 			deparseRangeTblRef(&join_sql_o, root, outerrel,
 							   fpinfo->make_outerrel_subquery,
-							   ignore_rel, ignore_conds, params_list);
+							   ignore_rel, ignore_conds, &additional_conds_o,
+							   params_list);
 
 			/*
 			 * If inner relation is the target relation, skip deparsing it.
@@ -1780,6 +1820,11 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				Assert(fpinfo->jointype == JOIN_INNER);
 				Assert(fpinfo->joinclauses == NIL);
 				appendBinaryStringInfo(buf, join_sql_o.data, join_sql_o.len);
+				if (additional_conds_o != NIL)
+				{
+					Assert(*additional_conds == NIL);
+					*additional_conds = additional_conds_o;
+				}
 				return;
 			}
 		}
@@ -1790,7 +1835,37 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 			initStringInfo(&join_sql_i);
 			deparseRangeTblRef(&join_sql_i, root, innerrel,
 							   fpinfo->make_innerrel_subquery,
-							   ignore_rel, ignore_conds, params_list);
+							   ignore_rel, ignore_conds, &additional_conds_i,
+							   params_list);
+
+			if (fpinfo->jointype == JOIN_SEMI)
+			{
+				deparse_expr_cxt context;
+				StringInfoData str;
+
+				initStringInfo(&str);
+				appendStringInfo(&str, "EXISTS (SELECT NULL FROM %s",
+								 join_sql_i.data);
+
+				context.buf = &str;
+				context.foreignrel = foreignrel;
+				context.scanrel = foreignrel;
+				context.root = root;
+				context.params_list = params_list;
+
+				appendWhereClause(fpinfo->joinclauses, additional_conds_i, &context);
+
+				if (additional_conds_i != NIL)
+				{
+					list_free_deep(additional_conds_i);
+					additional_conds_i = NIL;
+				}
+
+				/* Close parentheses for EXISTS subquery */
+				appendStringInfo(&str, ")");
+
+				*additional_conds = lappend(*additional_conds, str.data);
+			}
 
 			/*
 			 * If outer relation is the target relation, skip deparsing it.
@@ -1801,6 +1876,11 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				Assert(fpinfo->jointype == JOIN_INNER);
 				Assert(fpinfo->joinclauses == NIL);
 				appendBinaryStringInfo(buf, join_sql_i.data, join_sql_i.len);
+				if (additional_conds_i != NIL)
+				{
+					Assert(*additional_conds == NIL);
+					*additional_conds = additional_conds_i;
+				}
 				return;
 			}
 		}
@@ -1809,33 +1889,64 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		Assert(!outerrel_is_target && !innerrel_is_target);
 
 		/*
-		 * For a join relation FROM clause entry is deparsed as
-		 *
-		 * ((outer relation) <join type> (inner relation) ON (joinclauses))
+		 * For semijoin FROM clause is deparsed as an outer relation. An inner
+		 * relation and join clauses are converted to EXISTS condition and
+		 * passed to the upper level.
 		 */
-		appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
-						 get_jointype_name(fpinfo->jointype), join_sql_i.data);
-
-		/* Append join clause; (TRUE) if no join clause */
-		if (fpinfo->joinclauses)
+		if (fpinfo->jointype == JOIN_SEMI)
 		{
-			deparse_expr_cxt context;
+			appendStringInfo(buf, "%s", join_sql_o.data);
+		}
+		else
+		{
+			/*
+			 * For a join relation FROM clause entry is deparsed as
+			 *
+			 * ((outer relation) <join type> (inner relation) ON
+			 * (joinclauses))
+			 */
+			appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
+							 get_jointype_name(fpinfo->jointype), join_sql_i.data);
+
+			/* Append join clause; (TRUE) if no join clause */
+			if (fpinfo->joinclauses)
+			{
+				deparse_expr_cxt context;
 
-			context.buf = buf;
-			context.foreignrel = foreignrel;
-			context.scanrel = foreignrel;
-			context.root = root;
-			context.params_list = params_list;
+				context.buf = buf;
+				context.foreignrel = foreignrel;
+				context.scanrel = foreignrel;
+				context.root = root;
+				context.params_list = params_list;
 
-			appendStringInfoChar(buf, '(');
-			appendConditions(fpinfo->joinclauses, &context);
+				appendStringInfoChar(buf, '(');
+				appendConditions(fpinfo->joinclauses, &context);
+				appendStringInfoChar(buf, ')');
+			}
+			else
+				appendStringInfoString(buf, "(TRUE)");
+
+			/* End the FROM clause entry. */
 			appendStringInfoChar(buf, ')');
 		}
-		else
-			appendStringInfoString(buf, "(TRUE)");
 
-		/* End the FROM clause entry. */
-		appendStringInfoChar(buf, ')');
+		/*
+		 * Construct additional_conds from current level additional_conds and
+		 * additional_conds, coming from inner and outer rels.
+		 */
+		if (additional_conds_o != NIL)
+		{
+			*additional_conds = list_concat(*additional_conds,
+											additional_conds_o);
+			list_free(additional_conds_o);
+		}
+
+		if (additional_conds_i != NIL)
+		{
+			*additional_conds = list_concat(*additional_conds,
+											additional_conds_i);
+			list_free(additional_conds_i);
+		}
 	}
 	else
 	{
@@ -1867,7 +1978,7 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 static void
 deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				   bool make_subquery, Index ignore_rel, List **ignore_conds,
-				   List **params_list)
+				   List **additional_conds, List **params_list)
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
@@ -1925,7 +2036,8 @@ deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 	}
 	else
 		deparseFromExprForRel(buf, root, foreignrel, true, ignore_rel,
-							  ignore_conds, params_list);
+							  ignore_conds, additional_conds,
+							  params_list);
 }
 
 /*
@@ -2148,6 +2260,7 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 	RangeTblEntry *rte = planner_rt_fetch(rtindex, root);
 	ListCell   *lc,
 			   *lc2;
+	List	   *additional_conds = NIL;
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -2189,17 +2302,17 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 	{
 		List	   *ignore_conds = NIL;
 
+
 		appendStringInfoString(buf, " FROM ");
 		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
-							  &ignore_conds, params_list);
+							  &ignore_conds, &additional_conds, params_list);
 		remote_conds = list_concat(remote_conds, ignore_conds);
 	}
 
-	if (remote_conds)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(remote_conds, &context);
-	}
+	appendWhereClause(remote_conds, additional_conds, &context);
+
+	if (additional_conds != NIL)
+		list_free_deep(additional_conds);
 
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		deparseExplicitTargetList(returningList, true, retrieved_attrs,
@@ -2255,6 +2368,7 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 					   List **retrieved_attrs)
 {
 	deparse_expr_cxt context;
+	List	   *additional_conds = NIL;
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -2274,15 +2388,14 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 
 		appendStringInfoString(buf, " USING ");
 		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
-							  &ignore_conds, params_list);
+							  &ignore_conds, &additional_conds, params_list);
 		remote_conds = list_concat(remote_conds, ignore_conds);
 	}
 
-	if (remote_conds)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(remote_conds, &context);
-	}
+	appendWhereClause(remote_conds, additional_conds, &context);
+
+	if (additional_conds != NIL)
+		list_free_deep(additional_conds);
 
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		deparseExplicitTargetList(returningList, true, retrieved_attrs,
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 22cae37a1eb..36e8939076a 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -2001,23 +2001,16 @@ SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER B
    Remote SQL: SELECT r1.ctid, CASE WHEN (r1.*)::text IS NOT NULL THEN ROW(r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8) END, CASE WHEN (r2.*)::text IS NOT NULL THEN ROW(r2."C 1", r2.c2, r2.c3, r2.c4, r2.c5, r2.c6, r2.c7, r2.c8) END, r1."C 1", r1.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r2."C 1" = r1."C 1")))) ORDER BY r1.c3 ASC NULLS LAST, r1."C 1" ASC NULLS LAST LIMIT 10::bigint OFFSET 100::bigint
 (4 rows)
 
--- SEMI JOIN, not pushed down
+-- SEMI JOIN
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
-                                      QUERY PLAN                                       
----------------------------------------------------------------------------------------
- Limit
+                                                                                             QUERY PLAN                                                                                              
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
    Output: t1.c1
-   ->  Merge Semi Join
-         Output: t1.c1
-         Merge Cond: (t1.c1 = t2.c1)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1
-               Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-         ->  Foreign Scan on public.ft2 t2
-               Output: t2.c1
-               Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-(11 rows)
+   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
+   Remote SQL: SELECT r1."C 1" FROM "S 1"."T 1" r1 WHERE EXISTS (SELECT NULL FROM "S 1"."T 1" r2 WHERE ((r2."C 1" = r1."C 1"))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint OFFSET 100::bigint
+(4 rows)
 
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
  c1  
@@ -4056,23 +4049,13 @@ RESET enable_sort;
 -- subquery using immutable function (can be sent to remote)
 PREPARE st3(int) AS SELECT * FROM ft1 t1 WHERE t1.c1 < $2 AND t1.c3 IN (SELECT c3 FROM ft2 t2 WHERE c1 > $1 AND date(c5) = '1970-01-17'::date) ORDER BY c1;
 EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st3(10, 20);
-                                                      QUERY PLAN                                                       
------------------------------------------------------------------------------------------------------------------------
- Sort
+                                                                                                                                           QUERY PLAN                                                                                                                                            
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
    Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-   Sort Key: t1.c1
-   ->  Nested Loop Semi Join
-         Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-         Join Filter: (t2.c3 = t1.c3)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-               Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" WHERE (("C 1" < 20))
-         ->  Materialize
-               Output: t2.c3
-               ->  Foreign Scan on public.ft2 t2
-                     Output: t2.c3
-                     Remote SQL: SELECT c3 FROM "S 1"."T 1" WHERE (("C 1" > 10)) AND ((date(c5) = '1970-01-17'::date))
-(14 rows)
+   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" < 20)) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r3."C 1" > 10)) AND ((date(r3.c5) = '1970-01-17'::date)) AND ((r3.c3 = r1.c3))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
 
 EXECUTE st3(10, 20);
  c1 | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
@@ -4616,6 +4599,283 @@ explain (verbose, costs off) select * from ft3 f, loct3 l
                Index Cond: (l.f1 = 'foo'::text)
 (12 rows)
 
+-- ===================================================================
+-- test SEMI-JOIN pushdown
+-- ===================================================================
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+                                                                                                                                                QUERY PLAN                                                                                                                                                 
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r2.c1, r2.c2, r2.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r2 ON (((r1.c2 = r2.c1)) AND ((r1."C 1" > 900)))) WHERE EXISTS (SELECT NULL FROM "S 1"."T 4" r4 WHERE ((r1.c2 = r4.c1))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 916 |  6 | 00916 | Sat Jan 17 00:00:00 1970 PST | Sat Jan 17 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 926 |  6 | 00926 | Tue Jan 27 00:00:00 1970 PST | Tue Jan 27 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 936 |  6 | 00936 | Fri Feb 06 00:00:00 1970 PST | Fri Feb 06 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 946 |  6 | 00946 | Mon Feb 16 00:00:00 1970 PST | Mon Feb 16 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 956 |  6 | 00956 | Thu Feb 26 00:00:00 1970 PST | Thu Feb 26 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 966 |  6 | 00966 | Sun Mar 08 00:00:00 1970 PST | Sun Mar 08 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 976 |  6 | 00976 | Wed Mar 18 00:00:00 1970 PST | Wed Mar 18 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 986 |  6 | 00986 | Sat Mar 28 00:00:00 1970 PST | Sat Mar 28 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 996 |  6 | 00996 | Tue Apr 07 00:00:00 1970 PST | Tue Apr 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- The same query, different join order
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+                                                                                                                                                QUERY PLAN                                                                                                                                                 
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r4.c1, r4.c2, r4.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r4 ON (((r1.c2 = r4.c1)) AND ((r1."C 1" > 900)))) WHERE EXISTS (SELECT NULL FROM "S 1"."T 4" r5 WHERE ((r4.c1 = r5.c1))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 916 |  6 | 00916 | Sat Jan 17 00:00:00 1970 PST | Sat Jan 17 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 926 |  6 | 00926 | Tue Jan 27 00:00:00 1970 PST | Tue Jan 27 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 936 |  6 | 00936 | Fri Feb 06 00:00:00 1970 PST | Fri Feb 06 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 946 |  6 | 00946 | Mon Feb 16 00:00:00 1970 PST | Mon Feb 16 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 956 |  6 | 00956 | Thu Feb 26 00:00:00 1970 PST | Thu Feb 26 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 966 |  6 | 00966 | Sun Mar 08 00:00:00 1970 PST | Sun Mar 08 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 976 |  6 | 00976 | Wed Mar 18 00:00:00 1970 PST | Wed Mar 18 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 986 |  6 | 00986 | Sat Mar 28 00:00:00 1970 PST | Sat Mar 28 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 996 |  6 | 00996 | Tue Apr 07 00:00:00 1970 PST | Tue Apr 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- Left join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                  QUERY PLAN                                                                                                                                                                                  
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: (public.ft2) LEFT JOIN ((public.ft4) SEMI JOIN (public.ft5))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, s6.c1, s6.c2, s6.c3 FROM ("S 1"."T 1" r1 LEFT JOIN (SELECT r4.c1, r4.c2, r4.c3 FROM "S 1"."T 3" r4 WHERE EXISTS (SELECT NULL FROM "S 1"."T 4" r5 WHERE ((r4.c1 = r5.c1)))) s6(c1, c2, c3) ON (((r1.c2 = s6.c1)))) WHERE ((r1."C 1" > 900)) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 901 |  1 | 00901 | Fri Jan 02 00:00:00 1970 PST | Fri Jan 02 00:00:00 1970 | 1  | 1          | foo |    |    | 
+ 902 |  2 | 00902 | Sat Jan 03 00:00:00 1970 PST | Sat Jan 03 00:00:00 1970 | 2  | 2          | foo |    |    | 
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo |    |    | 
+ 904 |  4 | 00904 | Mon Jan 05 00:00:00 1970 PST | Mon Jan 05 00:00:00 1970 | 4  | 4          | foo |    |    | 
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo |    |    | 
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo |    |    | 
+ 908 |  8 | 00908 | Fri Jan 09 00:00:00 1970 PST | Fri Jan 09 00:00:00 1970 | 8  | 8          | foo |    |    | 
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo |    |    | 
+ 910 |  0 | 00910 | Sun Jan 11 00:00:00 1970 PST | Sun Jan 11 00:00:00 1970 | 0  | 0          | foo |    |    | 
+(10 rows)
+
+-- Several semi-joins per upper level join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                                                     QUERY PLAN                                                                                                                                                                                                                      
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)) INNER JOIN (public.ft5 ft5_1)) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r6.c1, r6.c2, r6.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r6 ON (((r1.c2 = r6.c1)) AND ((r1."C 1" > 900)))) INNER JOIN "S 1"."T 4" r8 ON (((r1.c2 <= r8.c1)))) WHERE EXISTS (SELECT NULL FROM "S 1"."T 3" r9 WHERE ((r8.c1 = r9.c1))) AND EXISTS (SELECT NULL FROM "S 1"."T 4" r7 WHERE ((r6.c1 = r7.c1))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- Semi-join below Semi-join
+EXPLAIN (verbose, costs off)
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                          QUERY PLAN                                                                                                                                                           
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8
+   Relations: (public.ft2) SEMI JOIN ((public.ft2 ft2_1) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" > 900)) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r1."C 1" = r3."C 1")) AND EXISTS (SELECT NULL FROM "S 1"."T 3" r4 WHERE ((r3.c2 = r4.c2)))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
+-----+----+-------+------------------------------+--------------------------+----+------------+-----
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo
+ 913 |  3 | 00913 | Wed Jan 14 00:00:00 1970 PST | Wed Jan 14 00:00:00 1970 | 3  | 3          | foo
+ 915 |  5 | 00915 | Fri Jan 16 00:00:00 1970 PST | Fri Jan 16 00:00:00 1970 | 5  | 5          | foo
+ 917 |  7 | 00917 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 919 |  9 | 00919 | Tue Jan 20 00:00:00 1970 PST | Tue Jan 20 00:00:00 1970 | 9  | 9          | foo
+ 923 |  3 | 00923 | Sat Jan 24 00:00:00 1970 PST | Sat Jan 24 00:00:00 1970 | 3  | 3          | foo
+ 925 |  5 | 00925 | Mon Jan 26 00:00:00 1970 PST | Mon Jan 26 00:00:00 1970 | 5  | 5          | foo
+(10 rows)
+
+-- Upper level relations shouldn't refer EXISTS() subqueries
+EXPLAIN (verbose, costs off)
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+                                                                                                                                                          QUERY PLAN                                                                                                                                                           
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ftupper.c1, ftupper.c2, ftupper.c3, ftupper.c4, ftupper.c5, ftupper.c6, ftupper.c7, ftupper.c8
+   Relations: (public.ft2 ftupper) SEMI JOIN ((public.ft2) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" > 900)) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r2 WHERE ((r1."C 1" = r2."C 1")) AND EXISTS (SELECT NULL FROM "S 1"."T 3" r3 WHERE ((r2.c2 = r3.c2)))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
+-----+----+-------+------------------------------+--------------------------+----+------------+-----
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo
+ 913 |  3 | 00913 | Wed Jan 14 00:00:00 1970 PST | Wed Jan 14 00:00:00 1970 | 3  | 3          | foo
+ 915 |  5 | 00915 | Fri Jan 16 00:00:00 1970 PST | Fri Jan 16 00:00:00 1970 | 5  | 5          | foo
+ 917 |  7 | 00917 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 919 |  9 | 00919 | Tue Jan 20 00:00:00 1970 PST | Tue Jan 20 00:00:00 1970 | 9  | 9          | foo
+ 923 |  3 | 00923 | Sat Jan 24 00:00:00 1970 PST | Sat Jan 24 00:00:00 1970 | 3  | 3          | foo
+ 925 |  5 | 00925 | Mon Jan 26 00:00:00 1970 PST | Mon Jan 26 00:00:00 1970 | 5  | 5          | foo
+(10 rows)
+
+-- EXISTS should be propogated to the highest upper inner join
+EXPLAIN (verbose, costs off)
+	SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                                                     QUERY PLAN                                                                                                                                                                                                                     
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft2 ft2_1)) INNER JOIN (public.ft2 ft2_2)) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r6.c1, r6.c2, r6.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r6 ON (((r1.c2 = r6.c1)) AND ((r1."C 1" > 900)))) INNER JOIN "S 1"."T 1" r8 ON (((r1.c2 = r8.c2)))) WHERE EXISTS (SELECT NULL FROM "S 1"."T 3" r9 WHERE ((r1.c2 = r9.c2))) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r7 WHERE ((r7.c2 = r6.c2))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+ c1 | c2 | c3 | c4 | c5 | c6 | c7 | c8 | c1 | c2 | c3 
+----+----+----+----+----+----+----+----+----+----+----
+(0 rows)
+
+-- Can't push down semi-join with inner rel vars in targetlist
+EXPLAIN (verbose, costs off)
+SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
+	ft1.c1 IN (
+		SELECT ft2.c1 FROM ft2 JOIN ft4 ON ft2.c1 = ft4.c1)
+	ORDER BY ft1.c1 LIMIT 5;
+                                                                            QUERY PLAN                                                                             
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Limit
+   Output: ft1.c1
+   ->  Merge Semi Join
+         Output: ft1.c1
+         Merge Cond: (ft1.c1 = ft2_1.c1)
+         ->  Foreign Scan
+               Output: ft1.c1, ft2.c1
+               Relations: (public.ft1) INNER JOIN (public.ft2)
+               Remote SQL: SELECT r1."C 1", r2."C 1" FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r2."C 1" = r1."C 1")))) ORDER BY r1."C 1" ASC NULLS LAST
+         ->  Foreign Scan
+               Output: ft2_1.c1, ft4.c1
+               Relations: (public.ft2 ft2_1) INNER JOIN (public.ft4)
+               Remote SQL: SELECT r5."C 1", r6.c1 FROM ("S 1"."T 1" r5 INNER JOIN "S 1"."T 3" r6 ON (((r5."C 1" = r6.c1)))) ORDER BY r5."C 1" ASC NULLS LAST
+(13 rows)
+
 -- ===================================================================
 -- test writable foreign table stuff
 -- ===================================================================
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 6de2bec3b7b..3b0ccbb22ca 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -779,6 +779,7 @@ postgresGetForeignRelSize(PlannerInfo *root,
 	fpinfo->make_outerrel_subquery = false;
 	fpinfo->make_innerrel_subquery = false;
 	fpinfo->lower_subquery_rels = NULL;
+	fpinfo->hidden_subquery_rels = NULL;
 	/* Set the relation index. */
 	fpinfo->relation_index = baserel->relid;
 }
@@ -5724,6 +5725,45 @@ postgresImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
 	return commands;
 }
 
+/*
+ * Check if reltarget is safe enough to push down semi-join.
+ * Reltarget is not safe, if it contains references
+ * to inner rel relids, which do not belong to outer rel.
+ */
+static bool
+semijoin_target_ok(PlannerInfo *root, RelOptInfo *joinrel, RelOptInfo *outerrel, RelOptInfo *innerrel)
+{
+	List	   *vars;
+	ListCell   *lc;
+	bool		ok = true;
+
+	Assert(joinrel->reltarget);
+
+	vars = pull_var_clause((Node *) joinrel->reltarget->exprs, PVC_INCLUDE_PLACEHOLDERS);
+
+	foreach(lc, vars)
+	{
+		Var		   *var = (Var *) lfirst(lc);
+
+		if (!IsA(var, Var))
+			continue;
+
+		if (bms_is_member(var->varno, innerrel->relids) &&
+			!bms_is_member(var->varno, outerrel->relids))
+		{
+			/*
+			 * Planner can create semi-joins, which refer to inner rel vars in
+			 * its target list. However, we deparse semi-join as exists()
+			 * subquery, so can't handle references to inner rel in target
+			 * list.
+			 */
+			ok = false;
+			break;
+		}
+	}
+	return ok;
+}
+
 /*
  * Assess whether the join between inner and outer relations can be pushed down
  * to the foreign server. As a side effect, save information we obtain in this
@@ -5741,12 +5781,19 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	List	   *joinclauses;
 
 	/*
-	 * We support pushing down INNER, LEFT, RIGHT and FULL OUTER joins.
-	 * Constructing queries representing SEMI and ANTI joins is hard, hence
-	 * not considered right now.
+	 * We support pushing down INNER, LEFT, RIGHT, FULL OUTER and SEMI joins.
+	 * Constructing queries representing ANTI joins is hard, hence not
+	 * considered right now.
 	 */
 	if (jointype != JOIN_INNER && jointype != JOIN_LEFT &&
-		jointype != JOIN_RIGHT && jointype != JOIN_FULL)
+		jointype != JOIN_RIGHT && jointype != JOIN_FULL &&
+		jointype != JOIN_SEMI)
+		return false;
+
+	/*
+	 * We can't push down semi-join if its reltarget is not safe
+	 */
+	if ((jointype == JOIN_SEMI) && !semijoin_target_ok(root, joinrel, outerrel, innerrel))
 		return false;
 
 	/*
@@ -5858,6 +5905,8 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	Assert(bms_is_subset(fpinfo_i->lower_subquery_rels, innerrel->relids));
 	fpinfo->lower_subquery_rels = bms_union(fpinfo_o->lower_subquery_rels,
 											fpinfo_i->lower_subquery_rels);
+	fpinfo->hidden_subquery_rels = bms_union(fpinfo_o->hidden_subquery_rels,
+											 fpinfo_i->hidden_subquery_rels);
 
 	/*
 	 * Pull the other remote conditions from the joining relations into join
@@ -5871,6 +5920,12 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	 * the joinclauses, since they need to be evaluated while constructing the
 	 * join.
 	 *
+	 * For SEMI-JOIN clauses from inner relation can not be added to
+	 * remote_conds, but should be treated as join clauses (as they are
+	 * deparsed to EXISTS subquery, where inner relation can be referred). A
+	 * list of relation ids, which can't be referred from higher levels, is
+	 * preserved as hidden_subquery_rels list.
+	 *
 	 * For a FULL OUTER JOIN, the other clauses from either relation can not
 	 * be added to the joinclauses or remote_conds, since each relation acts
 	 * as an outer relation for the other.
@@ -5901,6 +5956,16 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 											   fpinfo_i->remote_conds);
 			break;
 
+		case JOIN_SEMI:
+			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+											  fpinfo_i->remote_conds);
+			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+											  fpinfo->remote_conds);
+			fpinfo->remote_conds = list_copy(fpinfo_o->remote_conds);
+			fpinfo->hidden_subquery_rels = bms_union(fpinfo->hidden_subquery_rels,
+													 innerrel->relids);
+			break;
+
 		case JOIN_FULL:
 
 			/*
@@ -5943,6 +6008,24 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 		fpinfo->joinclauses = fpinfo->remote_conds;
 		fpinfo->remote_conds = NIL;
 	}
+	else if (jointype == JOIN_LEFT || jointype == JOIN_RIGHT || jointype == JOIN_FULL)
+	{
+		/*
+		 * Conditions, generated from semi-joins, should be evaluated before
+		 * LEFT/RIGHT/FULL join.
+		 */
+		if (!bms_is_empty(fpinfo_o->hidden_subquery_rels))
+		{
+			fpinfo->make_outerrel_subquery = true;
+			fpinfo->lower_subquery_rels = bms_add_members(fpinfo->lower_subquery_rels, outerrel->relids);
+		}
+
+		if (!bms_is_empty(fpinfo_i->hidden_subquery_rels))
+		{
+			fpinfo->make_innerrel_subquery = true;
+			fpinfo->lower_subquery_rels = bms_add_members(fpinfo->lower_subquery_rels, innerrel->relids);
+		}
+	}
 
 	/* Mark that this join can be pushed down safely */
 	fpinfo->pushdown_safe = true;
@@ -7692,6 +7775,8 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 {
 	ListCell   *lc;
 
+	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
+
 	foreach(lc, ec->ec_members)
 	{
 		EquivalenceMember *em = (EquivalenceMember *) lfirst(lc);
@@ -7702,6 +7787,7 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 		 */
 		if (bms_is_subset(em->em_relids, rel->relids) &&
 			!bms_is_empty(em->em_relids) &&
+			bms_is_empty(bms_intersect(em->em_relids, fpinfo->hidden_subquery_rels)) &&
 			is_foreign_expr(root, rel, em->em_expr))
 			return em;
 	}
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index 47157ac887e..d6e4d9e78de 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -118,6 +118,9 @@ typedef struct PgFdwRelationInfo
 										 * subquery? */
 	Relids		lower_subquery_rels;	/* all relids appearing in lower
 										 * subqueries */
+	Relids		hidden_subquery_rels;	/* relids, which can't be referred to
+										 * from upper relations, used
+										 * internally for em search */
 
 	/*
 	 * Index of the relation.  It is used to create an alias to a subquery
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 075da4ff867..cb405407028 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -600,7 +600,7 @@ WITH t (c1_1, c1_3, c2_1) AS MATERIALIZED (SELECT t1.c1, t1.c3, t2.c1 FROM ft1 t
 -- ctid with whole-row reference
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER BY t1.c3, t1.c1 OFFSET 100 LIMIT 10;
--- SEMI JOIN, not pushed down
+-- SEMI JOIN
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
@@ -1305,6 +1305,130 @@ explain (verbose, costs off) select * from ft3 where f2 = 'foo' COLLATE "C";
 explain (verbose, costs off) select * from ft3 f, loct3 l
   where f.f3 = l.f3 COLLATE "POSIX" and l.f1 = 'foo';
 
+-- ===================================================================
+-- test SEMI-JOIN pushdown
+-- ===================================================================
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+
+-- The same query, different join order
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+
+-- Left join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Several semi-joins per upper level join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Semi-join below Semi-join
+EXPLAIN (verbose, costs off)
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Upper level relations shouldn't refer EXISTS() subqueries
+EXPLAIN (verbose, costs off)
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+
+-- EXISTS should be propogated to the highest upper inner join
+EXPLAIN (verbose, costs off)
+	SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+
+-- Can't push down semi-join with inner rel vars in targetlist
+EXPLAIN (verbose, costs off)
+SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
+	ft1.c1 IN (
+		SELECT ft2.c1 FROM ft2 JOIN ft4 ON ft2.c1 = ft4.c1)
+	ORDER BY ft1.c1 LIMIT 5;
+
 -- ===================================================================
 -- test writable foreign table stuff
 -- ===================================================================
-- 
2.39.3 (Apple Git-145)

From c17e05d09d5721d22785ed11bed053162d67d967 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <a.pyhalov@postgrespro.ru>
Date: Mon, 27 Nov 2023 14:35:29 +0300
Subject: [PATCH] postgres_fdw: add support for deparsing semi joins

---
 contrib/postgres_fdw/deparse.c                | 234 ++++++++++---
 .../postgres_fdw/expected/postgres_fdw.out    | 320 ++++++++++++++++--
 contrib/postgres_fdw/postgres_fdw.c           |  94 ++++-
 contrib/postgres_fdw/postgres_fdw.h           |   3 +
 contrib/postgres_fdw/sql/postgres_fdw.sql     | 126 ++++++-
 5 files changed, 696 insertions(+), 81 deletions(-)

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index 09fd489a901..8670524578b 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -180,11 +180,15 @@ static void appendConditions(List *exprs, deparse_expr_cxt *context);
 static void deparseFromExprForRel(StringInfo buf, PlannerInfo *root,
 								  RelOptInfo *foreignrel, bool use_alias,
 								  Index ignore_rel, List **ignore_conds,
+								  List **additional_conds,
 								  List **params_list);
+static void appendWhereClause(List *exprs, List *additional_conds,
+							  deparse_expr_cxt *context);
 static void deparseFromExpr(List *quals, deparse_expr_cxt *context);
 static void deparseRangeTblRef(StringInfo buf, PlannerInfo *root,
 							   RelOptInfo *foreignrel, bool make_subquery,
-							   Index ignore_rel, List **ignore_conds, List **params_list);
+							   Index ignore_rel, List **ignore_conds,
+							   List **additional_conds, List **params_list);
 static void deparseAggref(Aggref *node, deparse_expr_cxt *context);
 static void appendGroupByClause(List *tlist, deparse_expr_cxt *context);
 static void appendOrderBySuffix(Oid sortop, Oid sortcoltype, bool nulls_first,
@@ -1370,6 +1374,7 @@ deparseFromExpr(List *quals, deparse_expr_cxt *context)
 {
 	StringInfo	buf = context->buf;
 	RelOptInfo *scanrel = context->scanrel;
+	List	   *additional_conds = NIL;
 
 	/* For upper relations, scanrel must be either a joinrel or a baserel */
 	Assert(!IS_UPPER_REL(context->foreignrel) ||
@@ -1379,14 +1384,11 @@ deparseFromExpr(List *quals, deparse_expr_cxt *context)
 	appendStringInfoString(buf, " FROM ");
 	deparseFromExprForRel(buf, context->root, scanrel,
 						  (bms_membership(scanrel->relids) == BMS_MULTIPLE),
-						  (Index) 0, NULL, context->params_list);
-
-	/* Construct WHERE clause */
-	if (quals != NIL)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(quals, context);
-	}
+						  (Index) 0, NULL, &additional_conds,
+						  context->params_list);
+	appendWhereClause(quals, additional_conds, context);
+	if (additional_conds != NIL)
+		list_free_deep(additional_conds);
 }
 
 /*
@@ -1598,6 +1600,42 @@ appendConditions(List *exprs, deparse_expr_cxt *context)
 	reset_transmission_modes(nestlevel);
 }
 
+/*
+ * Append WHERE clause, containing conditions
+ * from exprs and additional_conds, to context->buf.
+ */
+static void
+appendWhereClause(List *exprs, List *additional_conds, deparse_expr_cxt *context)
+{
+	StringInfo	buf = context->buf;
+	bool		need_and = false;
+	ListCell   *lc;
+
+	if (exprs != NIL || additional_conds != NIL)
+		appendStringInfoString(buf, " WHERE ");
+
+	/*
+	 * If there are some filters, append them.
+	 */
+	if (exprs != NIL)
+	{
+		appendConditions(exprs, context);
+		need_and = true;
+	}
+
+	/*
+	 * If there are some EXISTS conditions, coming from SEMI-JOINS, append
+	 * them.
+	 */
+	foreach(lc, additional_conds)
+	{
+		if (need_and)
+			appendStringInfoString(buf, " AND ");
+		appendStringInfoString(buf, (char *) lfirst(lc));
+		need_and = true;
+	}
+}
+
 /* Output join name for given join type */
 const char *
 get_jointype_name(JoinType jointype)
@@ -1616,6 +1654,9 @@ get_jointype_name(JoinType jointype)
 		case JOIN_FULL:
 			return "FULL";
 
+		case JOIN_SEMI:
+			return "SEMI";
+
 		default:
 			/* Shouldn't come here, but protect from buggy code. */
 			elog(ERROR, "unsupported join type %d", jointype);
@@ -1712,11 +1753,14 @@ deparseSubqueryTargetList(deparse_expr_cxt *context)
  * of DELETE; it deparses the join relation as if the relation never contained
  * the target relation, and creates a List of conditions to be deparsed into
  * the top-level WHERE clause, which is returned to *ignore_conds.
+ *
+ * 'additional_conds' is a pointer to list of strings to be appended to WHERE
+ * clause, coming from lower-level SEMI-JOINs.
  */
 static void
 deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 					  bool use_alias, Index ignore_rel, List **ignore_conds,
-					  List **params_list)
+					  List **additional_conds, List **params_list)
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
@@ -1728,6 +1772,8 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		RelOptInfo *innerrel = fpinfo->innerrel;
 		bool		outerrel_is_target = false;
 		bool		innerrel_is_target = false;
+		List	   *additional_conds_i = NIL;
+		List	   *additional_conds_o = NIL;
 
 		if (ignore_rel > 0 && bms_is_member(ignore_rel, foreignrel->relids))
 		{
@@ -1764,7 +1810,8 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 			initStringInfo(&join_sql_o);
 			deparseRangeTblRef(&join_sql_o, root, outerrel,
 							   fpinfo->make_outerrel_subquery,
-							   ignore_rel, ignore_conds, params_list);
+							   ignore_rel, ignore_conds, &additional_conds_o,
+							   params_list);
 
 			/*
 			 * If inner relation is the target relation, skip deparsing it.
@@ -1780,6 +1827,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				Assert(fpinfo->jointype == JOIN_INNER);
 				Assert(fpinfo->joinclauses == NIL);
 				appendBinaryStringInfo(buf, join_sql_o.data, join_sql_o.len);
+				/* Pass EXISTS conditions to upper level */
+				if (additional_conds_o != NIL)
+				{
+					Assert(*additional_conds == NIL);
+					*additional_conds = additional_conds_o;
+				}
 				return;
 			}
 		}
@@ -1790,7 +1843,54 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 			initStringInfo(&join_sql_i);
 			deparseRangeTblRef(&join_sql_i, root, innerrel,
 							   fpinfo->make_innerrel_subquery,
-							   ignore_rel, ignore_conds, params_list);
+							   ignore_rel, ignore_conds, &additional_conds_i,
+							   params_list);
+
+			/*
+			 * SEMI-JOIN is deparsed as EXISTS subquery. It references outer
+			 * and inner relations, so should be evaluated as condition in the
+			 * upper-level WHERE clause. We deparse the condition and pass it
+			 * to upper level callers as additional_conds list. Upper level
+			 * callers are responsible to insert conditions from the list
+			 * where appropriate.
+			 */
+			if (fpinfo->jointype == JOIN_SEMI)
+			{
+				deparse_expr_cxt context;
+				StringInfoData str;
+
+				/* Construct deparsed condition from this SEMI-JOIN */
+				initStringInfo(&str);
+				appendStringInfo(&str, "EXISTS (SELECT NULL FROM %s",
+								 join_sql_i.data);
+
+				context.buf = &str;
+				context.foreignrel = foreignrel;
+				context.scanrel = foreignrel;
+				context.root = root;
+				context.params_list = params_list;
+
+				/*
+				 * Append SEMI-JOIN clauses and EXISTS conditions from lower
+				 * levels to the current EXISTS subquery
+				 */
+				appendWhereClause(fpinfo->joinclauses, additional_conds_i, &context);
+
+				/*
+				 * EXISTS conditions, coming from lower join levels, has just
+				 * been processed.
+				 */
+				if (additional_conds_i != NIL)
+				{
+					list_free_deep(additional_conds_i);
+					additional_conds_i = NIL;
+				}
+
+				/* Close parentheses for EXISTS subquery */
+				appendStringInfo(&str, ")");
+
+				*additional_conds = lappend(*additional_conds, str.data);
+			}
 
 			/*
 			 * If outer relation is the target relation, skip deparsing it.
@@ -1801,6 +1901,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				Assert(fpinfo->jointype == JOIN_INNER);
 				Assert(fpinfo->joinclauses == NIL);
 				appendBinaryStringInfo(buf, join_sql_i.data, join_sql_i.len);
+				/* Pass EXISTS conditions to the upper call */
+				if (additional_conds_i != NIL)
+				{
+					Assert(*additional_conds == NIL);
+					*additional_conds = additional_conds_i;
+				}
 				return;
 			}
 		}
@@ -1809,33 +1915,65 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		Assert(!outerrel_is_target && !innerrel_is_target);
 
 		/*
-		 * For a join relation FROM clause entry is deparsed as
-		 *
-		 * ((outer relation) <join type> (inner relation) ON (joinclauses))
+		 * For semijoin FROM clause is deparsed as an outer relation. An inner
+		 * relation and join clauses are converted to EXISTS condition and
+		 * passed to the upper level.
 		 */
-		appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
-						 get_jointype_name(fpinfo->jointype), join_sql_i.data);
-
-		/* Append join clause; (TRUE) if no join clause */
-		if (fpinfo->joinclauses)
+		if (fpinfo->jointype == JOIN_SEMI)
 		{
-			deparse_expr_cxt context;
+			appendStringInfo(buf, "%s", join_sql_o.data);
+		}
+		else
+		{
+			/*
+			 * For a join relation FROM clause entry is deparsed as
+			 *
+			 * ((outer relation) <join type> (inner relation) ON
+			 * (joinclauses))
+			 */
+			appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
+							 get_jointype_name(fpinfo->jointype), join_sql_i.data);
 
-			context.buf = buf;
-			context.foreignrel = foreignrel;
-			context.scanrel = foreignrel;
-			context.root = root;
-			context.params_list = params_list;
+			/* Append join clause; (TRUE) if no join clause */
+			if (fpinfo->joinclauses)
+			{
+				deparse_expr_cxt context;
 
-			appendStringInfoChar(buf, '(');
-			appendConditions(fpinfo->joinclauses, &context);
+				context.buf = buf;
+				context.foreignrel = foreignrel;
+				context.scanrel = foreignrel;
+				context.root = root;
+				context.params_list = params_list;
+
+				appendStringInfoChar(buf, '(');
+				appendConditions(fpinfo->joinclauses, &context);
+				appendStringInfoChar(buf, ')');
+			}
+			else
+				appendStringInfoString(buf, "(TRUE)");
+
+			/* End the FROM clause entry. */
 			appendStringInfoChar(buf, ')');
 		}
-		else
-			appendStringInfoString(buf, "(TRUE)");
 
-		/* End the FROM clause entry. */
-		appendStringInfoChar(buf, ')');
+		/*
+		 * Construct additional_conds to be passed to the upper caller from
+		 * current level additional_conds and additional_conds, coming from
+		 * inner and outer rels.
+		 */
+		if (additional_conds_o != NIL)
+		{
+			*additional_conds = list_concat(*additional_conds,
+											additional_conds_o);
+			list_free(additional_conds_o);
+		}
+
+		if (additional_conds_i != NIL)
+		{
+			*additional_conds = list_concat(*additional_conds,
+											additional_conds_i);
+			list_free(additional_conds_i);
+		}
 	}
 	else
 	{
@@ -1863,11 +2001,13 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 
 /*
  * Append FROM clause entry for the given relation into buf.
+ * Conditions from lower-level SEMI-JOINs are appended to additional_conds
+ * and should be added to upper level WHERE clause.
  */
 static void
 deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				   bool make_subquery, Index ignore_rel, List **ignore_conds,
-				   List **params_list)
+				   List **additional_conds, List **params_list)
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
@@ -1925,7 +2065,8 @@ deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 	}
 	else
 		deparseFromExprForRel(buf, root, foreignrel, true, ignore_rel,
-							  ignore_conds, params_list);
+							  ignore_conds, additional_conds,
+							  params_list);
 }
 
 /*
@@ -2148,6 +2289,7 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 	RangeTblEntry *rte = planner_rt_fetch(rtindex, root);
 	ListCell   *lc,
 			   *lc2;
+	List	   *additional_conds = NIL;
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -2189,17 +2331,17 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 	{
 		List	   *ignore_conds = NIL;
 
+
 		appendStringInfoString(buf, " FROM ");
 		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
-							  &ignore_conds, params_list);
+							  &ignore_conds, &additional_conds, params_list);
 		remote_conds = list_concat(remote_conds, ignore_conds);
 	}
 
-	if (remote_conds)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(remote_conds, &context);
-	}
+	appendWhereClause(remote_conds, additional_conds, &context);
+
+	if (additional_conds != NIL)
+		list_free_deep(additional_conds);
 
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		deparseExplicitTargetList(returningList, true, retrieved_attrs,
@@ -2255,6 +2397,7 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 					   List **retrieved_attrs)
 {
 	deparse_expr_cxt context;
+	List	   *additional_conds = NIL;
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -2274,15 +2417,14 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 
 		appendStringInfoString(buf, " USING ");
 		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
-							  &ignore_conds, params_list);
+							  &ignore_conds, &additional_conds, params_list);
 		remote_conds = list_concat(remote_conds, ignore_conds);
 	}
 
-	if (remote_conds)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(remote_conds, &context);
-	}
+	appendWhereClause(remote_conds, additional_conds, &context);
+
+	if (additional_conds != NIL)
+		list_free_deep(additional_conds);
 
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		deparseExplicitTargetList(returningList, true, retrieved_attrs,
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 22cae37a1eb..36e8939076a 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -2001,23 +2001,16 @@ SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER B
    Remote SQL: SELECT r1.ctid, CASE WHEN (r1.*)::text IS NOT NULL THEN ROW(r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8) END, CASE WHEN (r2.*)::text IS NOT NULL THEN ROW(r2."C 1", r2.c2, r2.c3, r2.c4, r2.c5, r2.c6, r2.c7, r2.c8) END, r1."C 1", r1.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r2."C 1" = r1."C 1")))) ORDER BY r1.c3 ASC NULLS LAST, r1."C 1" ASC NULLS LAST LIMIT 10::bigint OFFSET 100::bigint
 (4 rows)
 
--- SEMI JOIN, not pushed down
+-- SEMI JOIN
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
-                                      QUERY PLAN                                       
----------------------------------------------------------------------------------------
- Limit
+                                                                                             QUERY PLAN                                                                                              
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
    Output: t1.c1
-   ->  Merge Semi Join
-         Output: t1.c1
-         Merge Cond: (t1.c1 = t2.c1)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1
-               Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-         ->  Foreign Scan on public.ft2 t2
-               Output: t2.c1
-               Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-(11 rows)
+   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
+   Remote SQL: SELECT r1."C 1" FROM "S 1"."T 1" r1 WHERE EXISTS (SELECT NULL FROM "S 1"."T 1" r2 WHERE ((r2."C 1" = r1."C 1"))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint OFFSET 100::bigint
+(4 rows)
 
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
  c1  
@@ -4056,23 +4049,13 @@ RESET enable_sort;
 -- subquery using immutable function (can be sent to remote)
 PREPARE st3(int) AS SELECT * FROM ft1 t1 WHERE t1.c1 < $2 AND t1.c3 IN (SELECT c3 FROM ft2 t2 WHERE c1 > $1 AND date(c5) = '1970-01-17'::date) ORDER BY c1;
 EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st3(10, 20);
-                                                      QUERY PLAN                                                       
------------------------------------------------------------------------------------------------------------------------
- Sort
+                                                                                                                                           QUERY PLAN                                                                                                                                            
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
    Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-   Sort Key: t1.c1
-   ->  Nested Loop Semi Join
-         Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-         Join Filter: (t2.c3 = t1.c3)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-               Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" WHERE (("C 1" < 20))
-         ->  Materialize
-               Output: t2.c3
-               ->  Foreign Scan on public.ft2 t2
-                     Output: t2.c3
-                     Remote SQL: SELECT c3 FROM "S 1"."T 1" WHERE (("C 1" > 10)) AND ((date(c5) = '1970-01-17'::date))
-(14 rows)
+   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" < 20)) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r3."C 1" > 10)) AND ((date(r3.c5) = '1970-01-17'::date)) AND ((r3.c3 = r1.c3))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
 
 EXECUTE st3(10, 20);
  c1 | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
@@ -4616,6 +4599,283 @@ explain (verbose, costs off) select * from ft3 f, loct3 l
                Index Cond: (l.f1 = 'foo'::text)
 (12 rows)
 
+-- ===================================================================
+-- test SEMI-JOIN pushdown
+-- ===================================================================
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+                                                                                                                                                QUERY PLAN                                                                                                                                                 
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r2.c1, r2.c2, r2.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r2 ON (((r1.c2 = r2.c1)) AND ((r1."C 1" > 900)))) WHERE EXISTS (SELECT NULL FROM "S 1"."T 4" r4 WHERE ((r1.c2 = r4.c1))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 916 |  6 | 00916 | Sat Jan 17 00:00:00 1970 PST | Sat Jan 17 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 926 |  6 | 00926 | Tue Jan 27 00:00:00 1970 PST | Tue Jan 27 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 936 |  6 | 00936 | Fri Feb 06 00:00:00 1970 PST | Fri Feb 06 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 946 |  6 | 00946 | Mon Feb 16 00:00:00 1970 PST | Mon Feb 16 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 956 |  6 | 00956 | Thu Feb 26 00:00:00 1970 PST | Thu Feb 26 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 966 |  6 | 00966 | Sun Mar 08 00:00:00 1970 PST | Sun Mar 08 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 976 |  6 | 00976 | Wed Mar 18 00:00:00 1970 PST | Wed Mar 18 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 986 |  6 | 00986 | Sat Mar 28 00:00:00 1970 PST | Sat Mar 28 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 996 |  6 | 00996 | Tue Apr 07 00:00:00 1970 PST | Tue Apr 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- The same query, different join order
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+                                                                                                                                                QUERY PLAN                                                                                                                                                 
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r4.c1, r4.c2, r4.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r4 ON (((r1.c2 = r4.c1)) AND ((r1."C 1" > 900)))) WHERE EXISTS (SELECT NULL FROM "S 1"."T 4" r5 WHERE ((r4.c1 = r5.c1))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 916 |  6 | 00916 | Sat Jan 17 00:00:00 1970 PST | Sat Jan 17 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 926 |  6 | 00926 | Tue Jan 27 00:00:00 1970 PST | Tue Jan 27 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 936 |  6 | 00936 | Fri Feb 06 00:00:00 1970 PST | Fri Feb 06 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 946 |  6 | 00946 | Mon Feb 16 00:00:00 1970 PST | Mon Feb 16 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 956 |  6 | 00956 | Thu Feb 26 00:00:00 1970 PST | Thu Feb 26 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 966 |  6 | 00966 | Sun Mar 08 00:00:00 1970 PST | Sun Mar 08 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 976 |  6 | 00976 | Wed Mar 18 00:00:00 1970 PST | Wed Mar 18 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 986 |  6 | 00986 | Sat Mar 28 00:00:00 1970 PST | Sat Mar 28 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 996 |  6 | 00996 | Tue Apr 07 00:00:00 1970 PST | Tue Apr 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- Left join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                  QUERY PLAN                                                                                                                                                                                  
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: (public.ft2) LEFT JOIN ((public.ft4) SEMI JOIN (public.ft5))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, s6.c1, s6.c2, s6.c3 FROM ("S 1"."T 1" r1 LEFT JOIN (SELECT r4.c1, r4.c2, r4.c3 FROM "S 1"."T 3" r4 WHERE EXISTS (SELECT NULL FROM "S 1"."T 4" r5 WHERE ((r4.c1 = r5.c1)))) s6(c1, c2, c3) ON (((r1.c2 = s6.c1)))) WHERE ((r1."C 1" > 900)) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 901 |  1 | 00901 | Fri Jan 02 00:00:00 1970 PST | Fri Jan 02 00:00:00 1970 | 1  | 1          | foo |    |    | 
+ 902 |  2 | 00902 | Sat Jan 03 00:00:00 1970 PST | Sat Jan 03 00:00:00 1970 | 2  | 2          | foo |    |    | 
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo |    |    | 
+ 904 |  4 | 00904 | Mon Jan 05 00:00:00 1970 PST | Mon Jan 05 00:00:00 1970 | 4  | 4          | foo |    |    | 
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo |    |    | 
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo |    |    | 
+ 908 |  8 | 00908 | Fri Jan 09 00:00:00 1970 PST | Fri Jan 09 00:00:00 1970 | 8  | 8          | foo |    |    | 
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo |    |    | 
+ 910 |  0 | 00910 | Sun Jan 11 00:00:00 1970 PST | Sun Jan 11 00:00:00 1970 | 0  | 0          | foo |    |    | 
+(10 rows)
+
+-- Several semi-joins per upper level join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                                                     QUERY PLAN                                                                                                                                                                                                                      
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)) INNER JOIN (public.ft5 ft5_1)) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r6.c1, r6.c2, r6.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r6 ON (((r1.c2 = r6.c1)) AND ((r1."C 1" > 900)))) INNER JOIN "S 1"."T 4" r8 ON (((r1.c2 <= r8.c1)))) WHERE EXISTS (SELECT NULL FROM "S 1"."T 3" r9 WHERE ((r8.c1 = r9.c1))) AND EXISTS (SELECT NULL FROM "S 1"."T 4" r7 WHERE ((r6.c1 = r7.c1))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- Semi-join below Semi-join
+EXPLAIN (verbose, costs off)
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                          QUERY PLAN                                                                                                                                                           
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8
+   Relations: (public.ft2) SEMI JOIN ((public.ft2 ft2_1) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" > 900)) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r1."C 1" = r3."C 1")) AND EXISTS (SELECT NULL FROM "S 1"."T 3" r4 WHERE ((r3.c2 = r4.c2)))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
+-----+----+-------+------------------------------+--------------------------+----+------------+-----
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo
+ 913 |  3 | 00913 | Wed Jan 14 00:00:00 1970 PST | Wed Jan 14 00:00:00 1970 | 3  | 3          | foo
+ 915 |  5 | 00915 | Fri Jan 16 00:00:00 1970 PST | Fri Jan 16 00:00:00 1970 | 5  | 5          | foo
+ 917 |  7 | 00917 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 919 |  9 | 00919 | Tue Jan 20 00:00:00 1970 PST | Tue Jan 20 00:00:00 1970 | 9  | 9          | foo
+ 923 |  3 | 00923 | Sat Jan 24 00:00:00 1970 PST | Sat Jan 24 00:00:00 1970 | 3  | 3          | foo
+ 925 |  5 | 00925 | Mon Jan 26 00:00:00 1970 PST | Mon Jan 26 00:00:00 1970 | 5  | 5          | foo
+(10 rows)
+
+-- Upper level relations shouldn't refer EXISTS() subqueries
+EXPLAIN (verbose, costs off)
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+                                                                                                                                                          QUERY PLAN                                                                                                                                                           
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ftupper.c1, ftupper.c2, ftupper.c3, ftupper.c4, ftupper.c5, ftupper.c6, ftupper.c7, ftupper.c8
+   Relations: (public.ft2 ftupper) SEMI JOIN ((public.ft2) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" > 900)) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r2 WHERE ((r1."C 1" = r2."C 1")) AND EXISTS (SELECT NULL FROM "S 1"."T 3" r3 WHERE ((r2.c2 = r3.c2)))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
+-----+----+-------+------------------------------+--------------------------+----+------------+-----
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo
+ 913 |  3 | 00913 | Wed Jan 14 00:00:00 1970 PST | Wed Jan 14 00:00:00 1970 | 3  | 3          | foo
+ 915 |  5 | 00915 | Fri Jan 16 00:00:00 1970 PST | Fri Jan 16 00:00:00 1970 | 5  | 5          | foo
+ 917 |  7 | 00917 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 919 |  9 | 00919 | Tue Jan 20 00:00:00 1970 PST | Tue Jan 20 00:00:00 1970 | 9  | 9          | foo
+ 923 |  3 | 00923 | Sat Jan 24 00:00:00 1970 PST | Sat Jan 24 00:00:00 1970 | 3  | 3          | foo
+ 925 |  5 | 00925 | Mon Jan 26 00:00:00 1970 PST | Mon Jan 26 00:00:00 1970 | 5  | 5          | foo
+(10 rows)
+
+-- EXISTS should be propogated to the highest upper inner join
+EXPLAIN (verbose, costs off)
+	SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                                                     QUERY PLAN                                                                                                                                                                                                                     
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft2 ft2_1)) INNER JOIN (public.ft2 ft2_2)) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r6.c1, r6.c2, r6.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r6 ON (((r1.c2 = r6.c1)) AND ((r1."C 1" > 900)))) INNER JOIN "S 1"."T 1" r8 ON (((r1.c2 = r8.c2)))) WHERE EXISTS (SELECT NULL FROM "S 1"."T 3" r9 WHERE ((r1.c2 = r9.c2))) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r7 WHERE ((r7.c2 = r6.c2))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+ c1 | c2 | c3 | c4 | c5 | c6 | c7 | c8 | c1 | c2 | c3 
+----+----+----+----+----+----+----+----+----+----+----
+(0 rows)
+
+-- Can't push down semi-join with inner rel vars in targetlist
+EXPLAIN (verbose, costs off)
+SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
+	ft1.c1 IN (
+		SELECT ft2.c1 FROM ft2 JOIN ft4 ON ft2.c1 = ft4.c1)
+	ORDER BY ft1.c1 LIMIT 5;
+                                                                            QUERY PLAN                                                                             
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Limit
+   Output: ft1.c1
+   ->  Merge Semi Join
+         Output: ft1.c1
+         Merge Cond: (ft1.c1 = ft2_1.c1)
+         ->  Foreign Scan
+               Output: ft1.c1, ft2.c1
+               Relations: (public.ft1) INNER JOIN (public.ft2)
+               Remote SQL: SELECT r1."C 1", r2."C 1" FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r2."C 1" = r1."C 1")))) ORDER BY r1."C 1" ASC NULLS LAST
+         ->  Foreign Scan
+               Output: ft2_1.c1, ft4.c1
+               Relations: (public.ft2 ft2_1) INNER JOIN (public.ft4)
+               Remote SQL: SELECT r5."C 1", r6.c1 FROM ("S 1"."T 1" r5 INNER JOIN "S 1"."T 3" r6 ON (((r5."C 1" = r6.c1)))) ORDER BY r5."C 1" ASC NULLS LAST
+(13 rows)
+
 -- ===================================================================
 -- test writable foreign table stuff
 -- ===================================================================
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 6de2bec3b7b..3b0ccbb22ca 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -779,6 +779,7 @@ postgresGetForeignRelSize(PlannerInfo *root,
 	fpinfo->make_outerrel_subquery = false;
 	fpinfo->make_innerrel_subquery = false;
 	fpinfo->lower_subquery_rels = NULL;
+	fpinfo->hidden_subquery_rels = NULL;
 	/* Set the relation index. */
 	fpinfo->relation_index = baserel->relid;
 }
@@ -5724,6 +5725,45 @@ postgresImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
 	return commands;
 }
 
+/*
+ * Check if reltarget is safe enough to push down semi-join.
+ * Reltarget is not safe, if it contains references
+ * to inner rel relids, which do not belong to outer rel.
+ */
+static bool
+semijoin_target_ok(PlannerInfo *root, RelOptInfo *joinrel, RelOptInfo *outerrel, RelOptInfo *innerrel)
+{
+	List	   *vars;
+	ListCell   *lc;
+	bool		ok = true;
+
+	Assert(joinrel->reltarget);
+
+	vars = pull_var_clause((Node *) joinrel->reltarget->exprs, PVC_INCLUDE_PLACEHOLDERS);
+
+	foreach(lc, vars)
+	{
+		Var		   *var = (Var *) lfirst(lc);
+
+		if (!IsA(var, Var))
+			continue;
+
+		if (bms_is_member(var->varno, innerrel->relids) &&
+			!bms_is_member(var->varno, outerrel->relids))
+		{
+			/*
+			 * Planner can create semi-joins, which refer to inner rel vars in
+			 * its target list. However, we deparse semi-join as exists()
+			 * subquery, so can't handle references to inner rel in target
+			 * list.
+			 */
+			ok = false;
+			break;
+		}
+	}
+	return ok;
+}
+
 /*
  * Assess whether the join between inner and outer relations can be pushed down
  * to the foreign server. As a side effect, save information we obtain in this
@@ -5741,12 +5781,19 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	List	   *joinclauses;
 
 	/*
-	 * We support pushing down INNER, LEFT, RIGHT and FULL OUTER joins.
-	 * Constructing queries representing SEMI and ANTI joins is hard, hence
-	 * not considered right now.
+	 * We support pushing down INNER, LEFT, RIGHT, FULL OUTER and SEMI joins.
+	 * Constructing queries representing ANTI joins is hard, hence not
+	 * considered right now.
 	 */
 	if (jointype != JOIN_INNER && jointype != JOIN_LEFT &&
-		jointype != JOIN_RIGHT && jointype != JOIN_FULL)
+		jointype != JOIN_RIGHT && jointype != JOIN_FULL &&
+		jointype != JOIN_SEMI)
+		return false;
+
+	/*
+	 * We can't push down semi-join if its reltarget is not safe
+	 */
+	if ((jointype == JOIN_SEMI) && !semijoin_target_ok(root, joinrel, outerrel, innerrel))
 		return false;
 
 	/*
@@ -5858,6 +5905,8 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	Assert(bms_is_subset(fpinfo_i->lower_subquery_rels, innerrel->relids));
 	fpinfo->lower_subquery_rels = bms_union(fpinfo_o->lower_subquery_rels,
 											fpinfo_i->lower_subquery_rels);
+	fpinfo->hidden_subquery_rels = bms_union(fpinfo_o->hidden_subquery_rels,
+											 fpinfo_i->hidden_subquery_rels);
 
 	/*
 	 * Pull the other remote conditions from the joining relations into join
@@ -5871,6 +5920,12 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	 * the joinclauses, since they need to be evaluated while constructing the
 	 * join.
 	 *
+	 * For SEMI-JOIN clauses from inner relation can not be added to
+	 * remote_conds, but should be treated as join clauses (as they are
+	 * deparsed to EXISTS subquery, where inner relation can be referred). A
+	 * list of relation ids, which can't be referred from higher levels, is
+	 * preserved as hidden_subquery_rels list.
+	 *
 	 * For a FULL OUTER JOIN, the other clauses from either relation can not
 	 * be added to the joinclauses or remote_conds, since each relation acts
 	 * as an outer relation for the other.
@@ -5901,6 +5956,16 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 											   fpinfo_i->remote_conds);
 			break;
 
+		case JOIN_SEMI:
+			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+											  fpinfo_i->remote_conds);
+			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+											  fpinfo->remote_conds);
+			fpinfo->remote_conds = list_copy(fpinfo_o->remote_conds);
+			fpinfo->hidden_subquery_rels = bms_union(fpinfo->hidden_subquery_rels,
+													 innerrel->relids);
+			break;
+
 		case JOIN_FULL:
 
 			/*
@@ -5943,6 +6008,24 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 		fpinfo->joinclauses = fpinfo->remote_conds;
 		fpinfo->remote_conds = NIL;
 	}
+	else if (jointype == JOIN_LEFT || jointype == JOIN_RIGHT || jointype == JOIN_FULL)
+	{
+		/*
+		 * Conditions, generated from semi-joins, should be evaluated before
+		 * LEFT/RIGHT/FULL join.
+		 */
+		if (!bms_is_empty(fpinfo_o->hidden_subquery_rels))
+		{
+			fpinfo->make_outerrel_subquery = true;
+			fpinfo->lower_subquery_rels = bms_add_members(fpinfo->lower_subquery_rels, outerrel->relids);
+		}
+
+		if (!bms_is_empty(fpinfo_i->hidden_subquery_rels))
+		{
+			fpinfo->make_innerrel_subquery = true;
+			fpinfo->lower_subquery_rels = bms_add_members(fpinfo->lower_subquery_rels, innerrel->relids);
+		}
+	}
 
 	/* Mark that this join can be pushed down safely */
 	fpinfo->pushdown_safe = true;
@@ -7692,6 +7775,8 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 {
 	ListCell   *lc;
 
+	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
+
 	foreach(lc, ec->ec_members)
 	{
 		EquivalenceMember *em = (EquivalenceMember *) lfirst(lc);
@@ -7702,6 +7787,7 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 		 */
 		if (bms_is_subset(em->em_relids, rel->relids) &&
 			!bms_is_empty(em->em_relids) &&
+			bms_is_empty(bms_intersect(em->em_relids, fpinfo->hidden_subquery_rels)) &&
 			is_foreign_expr(root, rel, em->em_expr))
 			return em;
 	}
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index 47157ac887e..d6e4d9e78de 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -118,6 +118,9 @@ typedef struct PgFdwRelationInfo
 										 * subquery? */
 	Relids		lower_subquery_rels;	/* all relids appearing in lower
 										 * subqueries */
+	Relids		hidden_subquery_rels;	/* relids, which can't be referred to
+										 * from upper relations, used
+										 * internally for em search */
 
 	/*
 	 * Index of the relation.  It is used to create an alias to a subquery
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 075da4ff867..cb405407028 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -600,7 +600,7 @@ WITH t (c1_1, c1_3, c2_1) AS MATERIALIZED (SELECT t1.c1, t1.c3, t2.c1 FROM ft1 t
 -- ctid with whole-row reference
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER BY t1.c3, t1.c1 OFFSET 100 LIMIT 10;
--- SEMI JOIN, not pushed down
+-- SEMI JOIN
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
@@ -1305,6 +1305,130 @@ explain (verbose, costs off) select * from ft3 where f2 = 'foo' COLLATE "C";
 explain (verbose, costs off) select * from ft3 f, loct3 l
   where f.f3 = l.f3 COLLATE "POSIX" and l.f1 = 'foo';
 
+-- ===================================================================
+-- test SEMI-JOIN pushdown
+-- ===================================================================
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+
+-- The same query, different join order
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+
+-- Left join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Several semi-joins per upper level join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Semi-join below Semi-join
+EXPLAIN (verbose, costs off)
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Upper level relations shouldn't refer EXISTS() subqueries
+EXPLAIN (verbose, costs off)
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+
+-- EXISTS should be propogated to the highest upper inner join
+EXPLAIN (verbose, costs off)
+	SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+
+-- Can't push down semi-join with inner rel vars in targetlist
+EXPLAIN (verbose, costs off)
+SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
+	ft1.c1 IN (
+		SELECT ft2.c1 FROM ft2 JOIN ft4 ON ft2.c1 = ft4.c1)
+	ORDER BY ft1.c1 LIMIT 5;
+
 -- ===================================================================
 -- test writable foreign table stuff
 -- ===================================================================
-- 
2.34.1

From 1d5e17801d830892827766ea06dbcbd32b4e745c Mon Sep 17 00:00:00 2001
From: Alexander Korotkov <akorotkov@postgresql.org>
Date: Sun, 3 Dec 2023 22:48:26 +0200
Subject: [PATCH] Add support for deparsing semi-joins to contrib/postgres_fdw

SEMI-JOIN is deparsed as the EXISTS subquery. It references outer and inner
relations, so it should be evaluated as the condition in the upper-level WHERE
clause. The signatures of deparseFromExprForRel() and deparseRangeTblRef() are
revised so that they can add conditions to the upper level.

PgFdwRelationInfo now has a hidden_subquery_rels field, referencing the relids
used in the inner parts of semi-join.  They can't be referred to from upper
relations and should be used internally for equivalence member searches.

The planner can create semi-joins, which refer to inner rel vars in its target
list. However, we deparse semi-join as an exists() subquery. So we skip the
case when the target list references to inner rel of semi-join.

Author: Alexander Pyhalov
Reviewed-by: Ashutosh Bapat, Ian Lawrence Barwick, Yuuki Fujii, Tomas Vondra
Discussion: https://postgr.es/m/c9e2a757cf3ac2333714eaf83a9cc184@postgrespro.ru
---
 contrib/postgres_fdw/deparse.c                | 234 ++++++++++---
 .../postgres_fdw/expected/postgres_fdw.out    | 320 ++++++++++++++++--
 contrib/postgres_fdw/postgres_fdw.c           |  94 ++++-
 contrib/postgres_fdw/postgres_fdw.h           |   4 +
 contrib/postgres_fdw/sql/postgres_fdw.sql     | 126 ++++++-
 5 files changed, 697 insertions(+), 81 deletions(-)

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index 09fd489a901..9de4db3d957 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -180,11 +180,15 @@ static void appendConditions(List *exprs, deparse_expr_cxt *context);
 static void deparseFromExprForRel(StringInfo buf, PlannerInfo *root,
 								  RelOptInfo *foreignrel, bool use_alias,
 								  Index ignore_rel, List **ignore_conds,
+								  List **additional_conds,
 								  List **params_list);
+static void appendWhereClause(List *exprs, List *additional_conds,
+							  deparse_expr_cxt *context);
 static void deparseFromExpr(List *quals, deparse_expr_cxt *context);
 static void deparseRangeTblRef(StringInfo buf, PlannerInfo *root,
 							   RelOptInfo *foreignrel, bool make_subquery,
-							   Index ignore_rel, List **ignore_conds, List **params_list);
+							   Index ignore_rel, List **ignore_conds,
+							   List **additional_conds, List **params_list);
 static void deparseAggref(Aggref *node, deparse_expr_cxt *context);
 static void appendGroupByClause(List *tlist, deparse_expr_cxt *context);
 static void appendOrderBySuffix(Oid sortop, Oid sortcoltype, bool nulls_first,
@@ -1370,6 +1374,7 @@ deparseFromExpr(List *quals, deparse_expr_cxt *context)
 {
 	StringInfo	buf = context->buf;
 	RelOptInfo *scanrel = context->scanrel;
+	List	   *additional_conds = NIL;
 
 	/* For upper relations, scanrel must be either a joinrel or a baserel */
 	Assert(!IS_UPPER_REL(context->foreignrel) ||
@@ -1379,14 +1384,11 @@ deparseFromExpr(List *quals, deparse_expr_cxt *context)
 	appendStringInfoString(buf, " FROM ");
 	deparseFromExprForRel(buf, context->root, scanrel,
 						  (bms_membership(scanrel->relids) == BMS_MULTIPLE),
-						  (Index) 0, NULL, context->params_list);
-
-	/* Construct WHERE clause */
-	if (quals != NIL)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(quals, context);
-	}
+						  (Index) 0, NULL, &additional_conds,
+						  context->params_list);
+	appendWhereClause(quals, additional_conds, context);
+	if (additional_conds != NIL)
+		list_free_deep(additional_conds);
 }
 
 /*
@@ -1598,6 +1600,42 @@ appendConditions(List *exprs, deparse_expr_cxt *context)
 	reset_transmission_modes(nestlevel);
 }
 
+/*
+ * Append WHERE clause, containing conditions from exprs and additional_conds,
+ * to context->buf.
+ */
+static void
+appendWhereClause(List *exprs, List *additional_conds, deparse_expr_cxt *context)
+{
+	StringInfo	buf = context->buf;
+	bool		need_and = false;
+	ListCell   *lc;
+
+	if (exprs != NIL || additional_conds != NIL)
+		appendStringInfoString(buf, " WHERE ");
+
+	/*
+	 * If there are some filters, append them.
+	 */
+	if (exprs != NIL)
+	{
+		appendConditions(exprs, context);
+		need_and = true;
+	}
+
+	/*
+	 * If there are some EXISTS conditions, coming from SEMI-JOINS, append
+	 * them.
+	 */
+	foreach(lc, additional_conds)
+	{
+		if (need_and)
+			appendStringInfoString(buf, " AND ");
+		appendStringInfoString(buf, (char *) lfirst(lc));
+		need_and = true;
+	}
+}
+
 /* Output join name for given join type */
 const char *
 get_jointype_name(JoinType jointype)
@@ -1616,6 +1654,9 @@ get_jointype_name(JoinType jointype)
 		case JOIN_FULL:
 			return "FULL";
 
+		case JOIN_SEMI:
+			return "SEMI";
+
 		default:
 			/* Shouldn't come here, but protect from buggy code. */
 			elog(ERROR, "unsupported join type %d", jointype);
@@ -1712,11 +1753,14 @@ deparseSubqueryTargetList(deparse_expr_cxt *context)
  * of DELETE; it deparses the join relation as if the relation never contained
  * the target relation, and creates a List of conditions to be deparsed into
  * the top-level WHERE clause, which is returned to *ignore_conds.
+ *
+ * 'additional_conds' is a pointer to a list of strings to be appended to
+ * the WHERE clause, coming from lower-level SEMI-JOINs.
  */
 static void
 deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 					  bool use_alias, Index ignore_rel, List **ignore_conds,
-					  List **params_list)
+					  List **additional_conds, List **params_list)
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
@@ -1728,6 +1772,8 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		RelOptInfo *innerrel = fpinfo->innerrel;
 		bool		outerrel_is_target = false;
 		bool		innerrel_is_target = false;
+		List	   *additional_conds_i = NIL;
+		List	   *additional_conds_o = NIL;
 
 		if (ignore_rel > 0 && bms_is_member(ignore_rel, foreignrel->relids))
 		{
@@ -1764,7 +1810,8 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 			initStringInfo(&join_sql_o);
 			deparseRangeTblRef(&join_sql_o, root, outerrel,
 							   fpinfo->make_outerrel_subquery,
-							   ignore_rel, ignore_conds, params_list);
+							   ignore_rel, ignore_conds, &additional_conds_o,
+							   params_list);
 
 			/*
 			 * If inner relation is the target relation, skip deparsing it.
@@ -1780,6 +1827,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				Assert(fpinfo->jointype == JOIN_INNER);
 				Assert(fpinfo->joinclauses == NIL);
 				appendBinaryStringInfo(buf, join_sql_o.data, join_sql_o.len);
+				/* Pass EXISTS conditions to upper level */
+				if (additional_conds_o != NIL)
+				{
+					Assert(*additional_conds == NIL);
+					*additional_conds = additional_conds_o;
+				}
 				return;
 			}
 		}
@@ -1790,7 +1843,54 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 			initStringInfo(&join_sql_i);
 			deparseRangeTblRef(&join_sql_i, root, innerrel,
 							   fpinfo->make_innerrel_subquery,
-							   ignore_rel, ignore_conds, params_list);
+							   ignore_rel, ignore_conds, &additional_conds_i,
+							   params_list);
+
+			/*
+			 * SEMI-JOIN is deparsed as the EXISTS subquery. It references
+			 * outer and inner relations, so it should be evaluated as the
+			 * condition in the upper-level WHERE clause. We deparse the
+			 * condition and pass it to upper level callers as an
+			 * additional_conds list. Upper level callers are responsible for
+			 * inserting conditions from the list where appropriate.
+			 */
+			if (fpinfo->jointype == JOIN_SEMI)
+			{
+				deparse_expr_cxt context;
+				StringInfoData str;
+
+				/* Construct deparsed condition from this SEMI-JOIN */
+				initStringInfo(&str);
+				appendStringInfo(&str, "EXISTS (SELECT NULL FROM %s",
+								 join_sql_i.data);
+
+				context.buf = &str;
+				context.foreignrel = foreignrel;
+				context.scanrel = foreignrel;
+				context.root = root;
+				context.params_list = params_list;
+
+				/*
+				 * Append SEMI-JOIN clauses and EXISTS conditions from lower
+				 * levels to the current EXISTS subquery
+				 */
+				appendWhereClause(fpinfo->joinclauses, additional_conds_i, &context);
+
+				/*
+				 * EXISTS conditions, coming from lower join levels, have just
+				 * been processed.
+				 */
+				if (additional_conds_i != NIL)
+				{
+					list_free_deep(additional_conds_i);
+					additional_conds_i = NIL;
+				}
+
+				/* Close parentheses for EXISTS subquery */
+				appendStringInfo(&str, ")");
+
+				*additional_conds = lappend(*additional_conds, str.data);
+			}
 
 			/*
 			 * If outer relation is the target relation, skip deparsing it.
@@ -1801,6 +1901,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				Assert(fpinfo->jointype == JOIN_INNER);
 				Assert(fpinfo->joinclauses == NIL);
 				appendBinaryStringInfo(buf, join_sql_i.data, join_sql_i.len);
+				/* Pass EXISTS conditions to the upper call */
+				if (additional_conds_i != NIL)
+				{
+					Assert(*additional_conds == NIL);
+					*additional_conds = additional_conds_i;
+				}
 				return;
 			}
 		}
@@ -1809,33 +1915,65 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 		Assert(!outerrel_is_target && !innerrel_is_target);
 
 		/*
-		 * For a join relation FROM clause entry is deparsed as
-		 *
-		 * ((outer relation) <join type> (inner relation) ON (joinclauses))
+		 * For semijoin FROM clause is deparsed as an outer relation. An inner
+		 * relation and join clauses are converted to EXISTS condition and
+		 * passed to the upper level.
 		 */
-		appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
-						 get_jointype_name(fpinfo->jointype), join_sql_i.data);
-
-		/* Append join clause; (TRUE) if no join clause */
-		if (fpinfo->joinclauses)
+		if (fpinfo->jointype == JOIN_SEMI)
 		{
-			deparse_expr_cxt context;
+			appendStringInfo(buf, "%s", join_sql_o.data);
+		}
+		else
+		{
+			/*
+			 * For a join relation FROM clause, entry is deparsed as
+			 *
+			 * ((outer relation) <join type> (inner relation) ON
+			 * (joinclauses))
+			 */
+			appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
+							 get_jointype_name(fpinfo->jointype), join_sql_i.data);
 
-			context.buf = buf;
-			context.foreignrel = foreignrel;
-			context.scanrel = foreignrel;
-			context.root = root;
-			context.params_list = params_list;
+			/* Append join clause; (TRUE) if no join clause */
+			if (fpinfo->joinclauses)
+			{
+				deparse_expr_cxt context;
 
-			appendStringInfoChar(buf, '(');
-			appendConditions(fpinfo->joinclauses, &context);
+				context.buf = buf;
+				context.foreignrel = foreignrel;
+				context.scanrel = foreignrel;
+				context.root = root;
+				context.params_list = params_list;
+
+				appendStringInfoChar(buf, '(');
+				appendConditions(fpinfo->joinclauses, &context);
+				appendStringInfoChar(buf, ')');
+			}
+			else
+				appendStringInfoString(buf, "(TRUE)");
+
+			/* End the FROM clause entry. */
 			appendStringInfoChar(buf, ')');
 		}
-		else
-			appendStringInfoString(buf, "(TRUE)");
 
-		/* End the FROM clause entry. */
-		appendStringInfoChar(buf, ')');
+		/*
+		 * Construct additional_conds to be passed to the upper caller from
+		 * current level additional_conds and additional_conds, coming from
+		 * inner and outer rels.
+		 */
+		if (additional_conds_o != NIL)
+		{
+			*additional_conds = list_concat(*additional_conds,
+											additional_conds_o);
+			list_free(additional_conds_o);
+		}
+
+		if (additional_conds_i != NIL)
+		{
+			*additional_conds = list_concat(*additional_conds,
+											additional_conds_i);
+			list_free(additional_conds_i);
+		}
 	}
 	else
 	{
@@ -1863,11 +2001,13 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 
 /*
  * Append FROM clause entry for the given relation into buf.
+ * Conditions from lower-level SEMI-JOINs are appended to additional_conds
+ * and should be added to upper level WHERE clause.
  */
 static void
 deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				   bool make_subquery, Index ignore_rel, List **ignore_conds,
-				   List **params_list)
+				   List **additional_conds, List **params_list)
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
@@ -1925,7 +2065,8 @@ deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 	}
 	else
 		deparseFromExprForRel(buf, root, foreignrel, true, ignore_rel,
-							  ignore_conds, params_list);
+							  ignore_conds, additional_conds,
+							  params_list);
 }
 
 /*
@@ -2148,6 +2289,7 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 	RangeTblEntry *rte = planner_rt_fetch(rtindex, root);
 	ListCell   *lc,
 			   *lc2;
+	List	   *additional_conds = NIL;
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -2189,17 +2331,17 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
 	{
 		List	   *ignore_conds = NIL;
 
+
 		appendStringInfoString(buf, " FROM ");
 		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
-							  &ignore_conds, params_list);
+							  &ignore_conds, &additional_conds, params_list);
 		remote_conds = list_concat(remote_conds, ignore_conds);
 	}
 
-	if (remote_conds)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(remote_conds, &context);
-	}
+	appendWhereClause(remote_conds, additional_conds, &context);
+
+	if (additional_conds != NIL)
+		list_free_deep(additional_conds);
 
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		deparseExplicitTargetList(returningList, true, retrieved_attrs,
@@ -2255,6 +2397,7 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 					   List **retrieved_attrs)
 {
 	deparse_expr_cxt context;
+	List	   *additional_conds = NIL;
 
 	/* Set up context struct for recursion */
 	context.root = root;
@@ -2274,15 +2417,14 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
 
 		appendStringInfoString(buf, " USING ");
 		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
-							  &ignore_conds, params_list);
+							  &ignore_conds, &additional_conds, params_list);
 		remote_conds = list_concat(remote_conds, ignore_conds);
 	}
 
-	if (remote_conds)
-	{
-		appendStringInfoString(buf, " WHERE ");
-		appendConditions(remote_conds, &context);
-	}
+	appendWhereClause(remote_conds, additional_conds, &context);
+
+	if (additional_conds != NIL)
+		list_free_deep(additional_conds);
 
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		deparseExplicitTargetList(returningList, true, retrieved_attrs,
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 0a5bdf8bcc0..c988745b926 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -2001,23 +2001,16 @@ SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER B
    Remote SQL: SELECT r1.ctid, CASE WHEN (r1.*)::text IS NOT NULL THEN ROW(r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8) END, CASE WHEN (r2.*)::text IS NOT NULL THEN ROW(r2."C 1", r2.c2, r2.c3, r2.c4, r2.c5, r2.c6, r2.c7, r2.c8) END, r1."C 1", r1.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r2."C 1" = r1."C 1")))) ORDER BY r1.c3 ASC NULLS LAST, r1."C 1" ASC NULLS LAST LIMIT 10::bigint OFFSET 100::bigint
 (4 rows)
 
--- SEMI JOIN, not pushed down
+-- SEMI JOIN
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
-                                      QUERY PLAN                                       
----------------------------------------------------------------------------------------
- Limit
+                                                                                             QUERY PLAN                                                                                              
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
    Output: t1.c1
-   ->  Merge Semi Join
-         Output: t1.c1
-         Merge Cond: (t1.c1 = t2.c1)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1
-               Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-         ->  Foreign Scan on public.ft2 t2
-               Output: t2.c1
-               Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
-(11 rows)
+   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
+   Remote SQL: SELECT r1."C 1" FROM "S 1"."T 1" r1 WHERE EXISTS (SELECT NULL FROM "S 1"."T 1" r2 WHERE ((r2."C 1" = r1."C 1"))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint OFFSET 100::bigint
+(4 rows)
 
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
  c1  
@@ -4056,23 +4049,13 @@ RESET enable_sort;
 -- subquery using immutable function (can be sent to remote)
 PREPARE st3(int) AS SELECT * FROM ft1 t1 WHERE t1.c1 < $2 AND t1.c3 IN (SELECT c3 FROM ft2 t2 WHERE c1 > $1 AND date(c5) = '1970-01-17'::date) ORDER BY c1;
 EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st3(10, 20);
-                                                      QUERY PLAN                                                       
------------------------------------------------------------------------------------------------------------------------
- Sort
+                                                                                                                                           QUERY PLAN                                                                                                                                            
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
    Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-   Sort Key: t1.c1
-   ->  Nested Loop Semi Join
-         Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-         Join Filter: (t2.c3 = t1.c3)
-         ->  Foreign Scan on public.ft1 t1
-               Output: t1.c1, t1.c2, t1.c3, t1.c4, t1.c5, t1.c6, t1.c7, t1.c8
-               Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" WHERE (("C 1" < 20))
-         ->  Materialize
-               Output: t2.c3
-               ->  Foreign Scan on public.ft2 t2
-                     Output: t2.c3
-                     Remote SQL: SELECT c3 FROM "S 1"."T 1" WHERE (("C 1" > 10)) AND ((date(c5) = '1970-01-17'::date))
-(14 rows)
+   Relations: (public.ft1 t1) SEMI JOIN (public.ft2 t2)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" < 20)) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r3."C 1" > 10)) AND ((date(r3.c5) = '1970-01-17'::date)) AND ((r3.c3 = r1.c3))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
 
 EXECUTE st3(10, 20);
  c1 | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
@@ -4616,6 +4599,283 @@ explain (verbose, costs off) select * from ft3 f, loct3 l
                Index Cond: (l.f1 = 'foo'::text)
 (12 rows)
 
+-- ===================================================================
+-- test SEMI-JOIN pushdown
+-- ===================================================================
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+                                                                                                                                                QUERY PLAN                                                                                                                                                 
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r2.c1, r2.c2, r2.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r2 ON (((r1.c2 = r2.c1)) AND ((r1."C 1" > 900)))) WHERE EXISTS (SELECT NULL FROM "S 1"."T 4" r4 WHERE ((r1.c2 = r4.c1))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 916 |  6 | 00916 | Sat Jan 17 00:00:00 1970 PST | Sat Jan 17 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 926 |  6 | 00926 | Tue Jan 27 00:00:00 1970 PST | Tue Jan 27 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 936 |  6 | 00936 | Fri Feb 06 00:00:00 1970 PST | Fri Feb 06 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 946 |  6 | 00946 | Mon Feb 16 00:00:00 1970 PST | Mon Feb 16 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 956 |  6 | 00956 | Thu Feb 26 00:00:00 1970 PST | Thu Feb 26 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 966 |  6 | 00966 | Sun Mar 08 00:00:00 1970 PST | Sun Mar 08 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 976 |  6 | 00976 | Wed Mar 18 00:00:00 1970 PST | Wed Mar 18 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 986 |  6 | 00986 | Sat Mar 28 00:00:00 1970 PST | Sat Mar 28 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 996 |  6 | 00996 | Tue Apr 07 00:00:00 1970 PST | Tue Apr 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- The same query, different join order
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+                                                                                                                                                QUERY PLAN                                                                                                                                                 
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r4.c1, r4.c2, r4.c3 FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r4 ON (((r1.c2 = r4.c1)) AND ((r1."C 1" > 900)))) WHERE EXISTS (SELECT NULL FROM "S 1"."T 4" r5 WHERE ((r4.c1 = r5.c1))) ORDER BY r1."C 1" ASC NULLS LAST
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 916 |  6 | 00916 | Sat Jan 17 00:00:00 1970 PST | Sat Jan 17 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 926 |  6 | 00926 | Tue Jan 27 00:00:00 1970 PST | Tue Jan 27 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 936 |  6 | 00936 | Fri Feb 06 00:00:00 1970 PST | Fri Feb 06 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 946 |  6 | 00946 | Mon Feb 16 00:00:00 1970 PST | Mon Feb 16 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 956 |  6 | 00956 | Thu Feb 26 00:00:00 1970 PST | Thu Feb 26 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 966 |  6 | 00966 | Sun Mar 08 00:00:00 1970 PST | Sun Mar 08 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 976 |  6 | 00976 | Wed Mar 18 00:00:00 1970 PST | Wed Mar 18 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 986 |  6 | 00986 | Sat Mar 28 00:00:00 1970 PST | Sat Mar 28 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 996 |  6 | 00996 | Tue Apr 07 00:00:00 1970 PST | Tue Apr 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- Left join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                  QUERY PLAN                                                                                                                                                                                  
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: (public.ft2) LEFT JOIN ((public.ft4) SEMI JOIN (public.ft5))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, s6.c1, s6.c2, s6.c3 FROM ("S 1"."T 1" r1 LEFT JOIN (SELECT r4.c1, r4.c2, r4.c3 FROM "S 1"."T 3" r4 WHERE EXISTS (SELECT NULL FROM "S 1"."T 4" r5 WHERE ((r4.c1 = r5.c1)))) s6(c1, c2, c3) ON (((r1.c2 = s6.c1)))) WHERE ((r1."C 1" > 900)) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 901 |  1 | 00901 | Fri Jan 02 00:00:00 1970 PST | Fri Jan 02 00:00:00 1970 | 1  | 1          | foo |    |    | 
+ 902 |  2 | 00902 | Sat Jan 03 00:00:00 1970 PST | Sat Jan 03 00:00:00 1970 | 2  | 2          | foo |    |    | 
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo |    |    | 
+ 904 |  4 | 00904 | Mon Jan 05 00:00:00 1970 PST | Mon Jan 05 00:00:00 1970 | 4  | 4          | foo |    |    | 
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo |    |    | 
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo |    |    | 
+ 908 |  8 | 00908 | Fri Jan 09 00:00:00 1970 PST | Fri Jan 09 00:00:00 1970 | 8  | 8          | foo |    |    | 
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo |    |    | 
+ 910 |  0 | 00910 | Sun Jan 11 00:00:00 1970 PST | Sun Jan 11 00:00:00 1970 | 0  | 0          | foo |    |    | 
+(10 rows)
+
+-- Several semi-joins per upper level join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                                                     QUERY PLAN                                                                                                                                                                                                                      
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft5)) INNER JOIN (public.ft5 ft5_1)) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r6.c1, r6.c2, r6.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r6 ON (((r1.c2 = r6.c1)) AND ((r1."C 1" > 900)))) INNER JOIN "S 1"."T 4" r8 ON (((r1.c2 <= r8.c1)))) WHERE EXISTS (SELECT NULL FROM "S 1"."T 3" r9 WHERE ((r8.c1 = r9.c1))) AND EXISTS (SELECT NULL FROM "S 1"."T 4" r7 WHERE ((r6.c1 = r7.c1))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2 |   c3   
+-----+----+-------+------------------------------+--------------------------+----+------------+-----+----+----+--------
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+ 906 |  6 | 00906 | Wed Jan 07 00:00:00 1970 PST | Wed Jan 07 00:00:00 1970 | 6  | 6          | foo |  6 |  7 | AAA006
+(10 rows)
+
+-- Semi-join below Semi-join
+EXPLAIN (verbose, costs off)
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                          QUERY PLAN                                                                                                                                                           
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8
+   Relations: (public.ft2) SEMI JOIN ((public.ft2 ft2_1) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" > 900)) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r3 WHERE ((r1."C 1" = r3."C 1")) AND EXISTS (SELECT NULL FROM "S 1"."T 3" r4 WHERE ((r3.c2 = r4.c2)))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
+-----+----+-------+------------------------------+--------------------------+----+------------+-----
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo
+ 913 |  3 | 00913 | Wed Jan 14 00:00:00 1970 PST | Wed Jan 14 00:00:00 1970 | 3  | 3          | foo
+ 915 |  5 | 00915 | Fri Jan 16 00:00:00 1970 PST | Fri Jan 16 00:00:00 1970 | 5  | 5          | foo
+ 917 |  7 | 00917 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 919 |  9 | 00919 | Tue Jan 20 00:00:00 1970 PST | Tue Jan 20 00:00:00 1970 | 9  | 9          | foo
+ 923 |  3 | 00923 | Sat Jan 24 00:00:00 1970 PST | Sat Jan 24 00:00:00 1970 | 3  | 3          | foo
+ 925 |  5 | 00925 | Mon Jan 26 00:00:00 1970 PST | Mon Jan 26 00:00:00 1970 | 5  | 5          | foo
+(10 rows)
+
+-- Upper level relations shouldn't refer EXISTS() subqueries
+EXPLAIN (verbose, costs off)
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+                                                                                                                                                          QUERY PLAN                                                                                                                                                           
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ftupper.c1, ftupper.c2, ftupper.c3, ftupper.c4, ftupper.c5, ftupper.c6, ftupper.c7, ftupper.c8
+   Relations: (public.ft2 ftupper) SEMI JOIN ((public.ft2) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8 FROM "S 1"."T 1" r1 WHERE ((r1."C 1" > 900)) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r2 WHERE ((r1."C 1" = r2."C 1")) AND EXISTS (SELECT NULL FROM "S 1"."T 3" r3 WHERE ((r2.c2 = r3.c2)))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+ c1  | c2 |  c3   |              c4              |            c5            | c6 |     c7     | c8  
+-----+----+-------+------------------------------+--------------------------+----+------------+-----
+ 903 |  3 | 00903 | Sun Jan 04 00:00:00 1970 PST | Sun Jan 04 00:00:00 1970 | 3  | 3          | foo
+ 905 |  5 | 00905 | Tue Jan 06 00:00:00 1970 PST | Tue Jan 06 00:00:00 1970 | 5  | 5          | foo
+ 907 |  7 | 00907 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 909 |  9 | 00909 | Sat Jan 10 00:00:00 1970 PST | Sat Jan 10 00:00:00 1970 | 9  | 9          | foo
+ 913 |  3 | 00913 | Wed Jan 14 00:00:00 1970 PST | Wed Jan 14 00:00:00 1970 | 3  | 3          | foo
+ 915 |  5 | 00915 | Fri Jan 16 00:00:00 1970 PST | Fri Jan 16 00:00:00 1970 | 5  | 5          | foo
+ 917 |  7 | 00917 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 919 |  9 | 00919 | Tue Jan 20 00:00:00 1970 PST | Tue Jan 20 00:00:00 1970 | 9  | 9          | foo
+ 923 |  3 | 00923 | Sat Jan 24 00:00:00 1970 PST | Sat Jan 24 00:00:00 1970 | 3  | 3          | foo
+ 925 |  5 | 00925 | Mon Jan 26 00:00:00 1970 PST | Mon Jan 26 00:00:00 1970 | 5  | 5          | foo
+(10 rows)
+
+-- EXISTS should be propogated to the highest upper inner join
+EXPLAIN (verbose, costs off)
+	SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+                                                                                                                                                                                                                     QUERY PLAN                                                                                                                                                                                                                     
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.c1, ft4.c2, ft4.c3
+   Relations: ((((public.ft2) INNER JOIN (public.ft4)) SEMI JOIN (public.ft2 ft2_1)) INNER JOIN (public.ft2 ft2_2)) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8, r6.c1, r6.c2, r6.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r6 ON (((r1.c2 = r6.c1)) AND ((r1."C 1" > 900)))) INNER JOIN "S 1"."T 1" r8 ON (((r1.c2 = r8.c2)))) WHERE EXISTS (SELECT NULL FROM "S 1"."T 3" r9 WHERE ((r1.c2 = r9.c2))) AND EXISTS (SELECT NULL FROM "S 1"."T 1" r7 WHERE ((r7.c2 = r6.c2))) ORDER BY r1."C 1" ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+ c1 | c2 | c3 | c4 | c5 | c6 | c7 | c8 | c1 | c2 | c3 
+----+----+----+----+----+----+----+----+----+----+----
+(0 rows)
+
+-- Can't push down semi-join with inner rel vars in targetlist
+EXPLAIN (verbose, costs off)
+SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
+	ft1.c1 IN (
+		SELECT ft2.c1 FROM ft2 JOIN ft4 ON ft2.c1 = ft4.c1)
+	ORDER BY ft1.c1 LIMIT 5;
+                                                                            QUERY PLAN                                                                             
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Limit
+   Output: ft1.c1
+   ->  Merge Semi Join
+         Output: ft1.c1
+         Merge Cond: (ft1.c1 = ft2_1.c1)
+         ->  Foreign Scan
+               Output: ft1.c1, ft2.c1
+               Relations: (public.ft1) INNER JOIN (public.ft2)
+               Remote SQL: SELECT r1."C 1", r2."C 1" FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r2."C 1" = r1."C 1")))) ORDER BY r1."C 1" ASC NULLS LAST
+         ->  Foreign Scan
+               Output: ft2_1.c1, ft4.c1
+               Relations: (public.ft2 ft2_1) INNER JOIN (public.ft4)
+               Remote SQL: SELECT r5."C 1", r6.c1 FROM ("S 1"."T 1" r5 INNER JOIN "S 1"."T 3" r6 ON (((r5."C 1" = r6.c1)))) ORDER BY r5."C 1" ASC NULLS LAST
+(13 rows)
+
 -- ===================================================================
 -- test writable foreign table stuff
 -- ===================================================================
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 6de2bec3b7b..8970b19211c 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -779,6 +779,7 @@ postgresGetForeignRelSize(PlannerInfo *root,
 	fpinfo->make_outerrel_subquery = false;
 	fpinfo->make_innerrel_subquery = false;
 	fpinfo->lower_subquery_rels = NULL;
+	fpinfo->hidden_subquery_rels = NULL;
 	/* Set the relation index. */
 	fpinfo->relation_index = baserel->relid;
 }
@@ -5724,6 +5725,45 @@ postgresImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
 	return commands;
 }
 
+/*
+ * Check if reltarget is safe enough to push down semi-join.  Reltarget is not
+ * safe, if it contains references to inner rel relids, which do not belong to
+ * outer rel.
+ */
+static bool
+semijoin_target_ok(PlannerInfo *root, RelOptInfo *joinrel, RelOptInfo *outerrel, RelOptInfo *innerrel)
+{
+	List	   *vars;
+	ListCell   *lc;
+	bool		ok = true;
+
+	Assert(joinrel->reltarget);
+
+	vars = pull_var_clause((Node *) joinrel->reltarget->exprs, PVC_INCLUDE_PLACEHOLDERS);
+
+	foreach(lc, vars)
+	{
+		Var		   *var = (Var *) lfirst(lc);
+
+		if (!IsA(var, Var))
+			continue;
+
+		if (bms_is_member(var->varno, innerrel->relids) &&
+			!bms_is_member(var->varno, outerrel->relids))
+		{
+			/*
+			 * The planner can create semi-joins, which refer to inner rel
+			 * vars in its target list. However, we deparse semi-join as an
+			 * exists() subquery, so can't handle references to inner rel in
+			 * the target list.
+			 */
+			ok = false;
+			break;
+		}
+	}
+	return ok;
+}
+
 /*
  * Assess whether the join between inner and outer relations can be pushed down
  * to the foreign server. As a side effect, save information we obtain in this
@@ -5741,12 +5781,19 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	List	   *joinclauses;
 
 	/*
-	 * We support pushing down INNER, LEFT, RIGHT and FULL OUTER joins.
-	 * Constructing queries representing SEMI and ANTI joins is hard, hence
-	 * not considered right now.
+	 * We support pushing down INNER, LEFT, RIGHT, FULL OUTER and SEMI joins.
+	 * Constructing queries representing ANTI joins is hard, hence not
+	 * considered right now.
 	 */
 	if (jointype != JOIN_INNER && jointype != JOIN_LEFT &&
-		jointype != JOIN_RIGHT && jointype != JOIN_FULL)
+		jointype != JOIN_RIGHT && jointype != JOIN_FULL &&
+		jointype != JOIN_SEMI)
+		return false;
+
+	/*
+	 * We can't push down semi-join if its reltarget is not safe
+	 */
+	if ((jointype == JOIN_SEMI) && !semijoin_target_ok(root, joinrel, outerrel, innerrel))
 		return false;
 
 	/*
@@ -5858,6 +5905,8 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	Assert(bms_is_subset(fpinfo_i->lower_subquery_rels, innerrel->relids));
 	fpinfo->lower_subquery_rels = bms_union(fpinfo_o->lower_subquery_rels,
 											fpinfo_i->lower_subquery_rels);
+	fpinfo->hidden_subquery_rels = bms_union(fpinfo_o->hidden_subquery_rels,
+											 fpinfo_i->hidden_subquery_rels);
 
 	/*
 	 * Pull the other remote conditions from the joining relations into join
@@ -5871,6 +5920,12 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	 * the joinclauses, since they need to be evaluated while constructing the
 	 * join.
 	 *
+	 * For SEMI-JOIN clauses from inner relation can not be added to
+	 * remote_conds, but should be treated as join clauses (as they are
+	 * deparsed to EXISTS subquery, where inner relation can be referred). A
+	 * list of relation ids, which can't be referred to from higher levels, is
+	 * preserved as a hidden_subquery_rels list.
+	 *
 	 * For a FULL OUTER JOIN, the other clauses from either relation can not
 	 * be added to the joinclauses or remote_conds, since each relation acts
 	 * as an outer relation for the other.
@@ -5901,6 +5956,16 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 											   fpinfo_i->remote_conds);
 			break;
 
+		case JOIN_SEMI:
+			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+											  fpinfo_i->remote_conds);
+			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+											  fpinfo->remote_conds);
+			fpinfo->remote_conds = list_copy(fpinfo_o->remote_conds);
+			fpinfo->hidden_subquery_rels = bms_union(fpinfo->hidden_subquery_rels,
+													 innerrel->relids);
+			break;
+
 		case JOIN_FULL:
 
 			/*
@@ -5943,6 +6008,24 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 		fpinfo->joinclauses = fpinfo->remote_conds;
 		fpinfo->remote_conds = NIL;
 	}
+	else if (jointype == JOIN_LEFT || jointype == JOIN_RIGHT || jointype == JOIN_FULL)
+	{
+		/*
+		 * Conditions, generated from semi-joins, should be evaluated before
+		 * LEFT/RIGHT/FULL join.
+		 */
+		if (!bms_is_empty(fpinfo_o->hidden_subquery_rels))
+		{
+			fpinfo->make_outerrel_subquery = true;
+			fpinfo->lower_subquery_rels = bms_add_members(fpinfo->lower_subquery_rels, outerrel->relids);
+		}
+
+		if (!bms_is_empty(fpinfo_i->hidden_subquery_rels))
+		{
+			fpinfo->make_innerrel_subquery = true;
+			fpinfo->lower_subquery_rels = bms_add_members(fpinfo->lower_subquery_rels, innerrel->relids);
+		}
+	}
 
 	/* Mark that this join can be pushed down safely */
 	fpinfo->pushdown_safe = true;
@@ -7692,6 +7775,8 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 {
 	ListCell   *lc;
 
+	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
+
 	foreach(lc, ec->ec_members)
 	{
 		EquivalenceMember *em = (EquivalenceMember *) lfirst(lc);
@@ -7702,6 +7787,7 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 		 */
 		if (bms_is_subset(em->em_relids, rel->relids) &&
 			!bms_is_empty(em->em_relids) &&
+			bms_is_empty(bms_intersect(em->em_relids, fpinfo->hidden_subquery_rels)) &&
 			is_foreign_expr(root, rel, em->em_expr))
 			return em;
 	}
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index 47157ac887e..9a1a80aebb4 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -118,6 +118,10 @@ typedef struct PgFdwRelationInfo
 										 * subquery? */
 	Relids		lower_subquery_rels;	/* all relids appearing in lower
 										 * subqueries */
+	Relids		hidden_subquery_rels;	/* relids, which can't be referred to
+										 * from upper relations, used
+										 * internally for equivalence member
+										 * search */
 
 	/*
 	 * Index of the relation.  It is used to create an alias to a subquery
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 075da4ff867..cb405407028 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -600,7 +600,7 @@ WITH t (c1_1, c1_3, c2_1) AS MATERIALIZED (SELECT t1.c1, t1.c3, t2.c1 FROM ft1 t
 -- ctid with whole-row reference
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER BY t1.c3, t1.c1 OFFSET 100 LIMIT 10;
--- SEMI JOIN, not pushed down
+-- SEMI JOIN
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
 SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
@@ -1305,6 +1305,130 @@ explain (verbose, costs off) select * from ft3 where f2 = 'foo' COLLATE "C";
 explain (verbose, costs off) select * from ft3 f, loct3 l
   where f.f3 = l.f3 COLLATE "POSIX" and l.f1 = 'foo';
 
+-- ===================================================================
+-- test SEMI-JOIN pushdown
+-- ===================================================================
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
+  ORDER BY ft2.c1;
+
+-- The same query, different join order
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1;
+
+-- Left join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Several semi-joins per upper level join
+EXPLAIN (verbose, costs off)
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+  (SELECT * FROM ft4 WHERE
+  EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
+  ON ft2.c2 = ft4.c1
+  INNER JOIN (SELECT * FROM ft5 WHERE
+  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
+  ON ft2.c2 <= ft5.c1
+  WHERE ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Semi-join below Semi-join
+EXPLAIN (verbose, costs off)
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.* FROM ft2 WHERE
+  c1 = ANY (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
+  AND ft2.c1 > 900
+  ORDER BY ft2.c1 LIMIT 10;
+
+-- Upper level relations shouldn't refer EXISTS() subqueries
+EXPLAIN (verbose, costs off)
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+SELECT * FROM ft2 ftupper WHERE
+   EXISTS (
+	SELECT c1 FROM ft2 WHERE
+	  EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
+  AND ftupper.c1 > 900
+  ORDER BY ftupper.c1 LIMIT 10;
+
+-- EXISTS should be propogated to the highest upper inner join
+EXPLAIN (verbose, costs off)
+	SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
+	(SELECT * FROM ft4 WHERE EXISTS (
+		SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
+	ON ft2.c2 = ft4.c1
+	INNER JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (
+		SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
+	ON ft2.c2 = ft21.c2
+	WHERE ft2.c1 > 900
+	ORDER BY ft2.c1 LIMIT 10;
+
+-- Can't push down semi-join with inner rel vars in targetlist
+EXPLAIN (verbose, costs off)
+SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
+	ft1.c1 IN (
+		SELECT ft2.c1 FROM ft2 JOIN ft4 ON ft2.c1 = ft4.c1)
+	ORDER BY ft1.c1 LIMIT 5;
+
 -- ===================================================================
 -- test writable foreign table stuff
 -- ===================================================================
-- 
2.39.3 (Apple Git-145)

From 04c89be4b2802a0b51b10ca4828108a338c77e71 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <a.pyhalov@postgrespro.ru>
Date: Tue, 18 Mar 2025 13:46:08 +0300
Subject: [PATCH] Avoid pulling up restrict infos from subqueries

Semi-join joins below left/right join are deparsed as
subqueries. We can't refer to subqueries vars from upper relations,
so avoid pulling conditions from them.
---
 .../postgres_fdw/expected/postgres_fdw.out    | 39 +++++++++++++++++++
 contrib/postgres_fdw/postgres_fdw.c           | 22 +++++++++--
 contrib/postgres_fdw/sql/postgres_fdw.sql     | 18 +++++++++
 3 files changed, 75 insertions(+), 4 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index bb4ed3059c4..88385e06f31 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -4936,6 +4936,45 @@ SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
 ----+----+----+----+----+----+----+----+----+----+----
 (0 rows)
 
+-- semi-join conditions shouldn't pop up as
+-- left/right join join clause
+set enable_material to off;
+EXPLAIN (verbose, costs off)
+	SELECT NULL FROM
+	(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft2.c1 < 10))
+	RIGHT JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft2.c1 < 10))
+	ON (TRUE)
+LIMIT 10;
+                                                                                                                                        QUERY PLAN                                                                                                                                         
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: NULL::text
+   Relations: ((public.ft2 ft2_1) SEMI JOIN (public.ft4 ft4_1)) LEFT JOIN ((public.ft2) SEMI JOIN (public.ft4))
+   Remote SQL: SELECT NULL FROM ((SELECT NULL FROM "S 1"."T 1" r6 WHERE ((r6."C 1" < 10)) AND EXISTS (SELECT NULL FROM "S 1"."T 3" r7)) s8 LEFT JOIN (SELECT NULL FROM "S 1"."T 1" r4 WHERE ((r4."C 1" < 10)) AND EXISTS (SELECT NULL FROM "S 1"."T 3" r5)) s9 ON (TRUE)) LIMIT 10::bigint
+(4 rows)
+
+SELECT NULL FROM
+	(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft2.c1 < 10))
+	RIGHT JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft2.c1 < 10))
+	ON (TRUE)
+LIMIT 10;
+ ?column? 
+----------
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+(10 rows)
+
+reset enable_material;
 -- Can't push down semi-join with inner rel vars in targetlist
 EXPLAIN (verbose, costs off)
 SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 1131a8bf77e..8af8b802a24 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -5964,16 +5964,30 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 			break;
 
 		case JOIN_LEFT:
-			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+			/*
+			 * When semi-join is involved in inner or outer part of left join,
+			 * it's deparsed as a subquery and we can't refer to its vars
+			 * on upper level
+			 */
+			if (bms_is_empty(fpinfo_i->hidden_subquery_rels))
+				fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
 											  fpinfo_i->remote_conds);
-			fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
+			if (bms_is_empty(fpinfo_o->hidden_subquery_rels))
+				fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
 											   fpinfo_o->remote_conds);
 			break;
 
 		case JOIN_RIGHT:
-			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+			/*
+			 * When semi-join is involved in inner or outer part of right join,
+			 * it's deparsed as a subquery and we can't refer to its vars
+			 * on upper level
+			 */
+			if (bms_is_empty(fpinfo_o->hidden_subquery_rels))
+				fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
 											  fpinfo_o->remote_conds);
-			fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
+			if (bms_is_empty(fpinfo_i->hidden_subquery_rels))
+				fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
 											   fpinfo_i->remote_conds);
 			break;
 
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index d45e9f8ab52..faedeab9d41 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -1455,6 +1455,24 @@ SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
 	WHERE ft2.c1 > 900
 	ORDER BY ft2.c1 LIMIT 10;
 
+-- semi-join conditions shouldn't pop up as
+-- left/right join join clause
+set enable_material to off;
+EXPLAIN (verbose, costs off)
+	SELECT NULL FROM
+	(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft2.c1 < 10))
+	RIGHT JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft2.c1 < 10))
+	ON (TRUE)
+LIMIT 10;
+SELECT NULL FROM
+	(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft2.c1 < 10))
+	RIGHT JOIN
+	(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft2.c1 < 10))
+	ON (TRUE)
+LIMIT 10;
+reset enable_material;
+
 -- Can't push down semi-join with inner rel vars in targetlist
 EXPLAIN (verbose, costs off)
 SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
-- 
2.43.0

From 510031bfa9eba3726cc93ddf05c1d9217b4e1585 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <a.pyhalov@postgrespro.ru>
Date: Tue, 18 Mar 2025 13:46:08 +0300
Subject: [PATCH v2] Avoid pulling up restrict infos from subqueries

Semi-join joins below left/right join are deparsed as subqueries.  Thus,
we can't refer to subqueries vars from upper relations.  This commit avoids
pulling conditions from them.

Reported-by: Robins Tharakan <tharakan@gmail.com>
Bug: #18852
Discussion: https://postgr.es/m/CAEP4nAzryLd3gwcUpFBAG9MWyDfMRX8ZjuyY2XXjyC_C6k%2B_Zw%40mail.gmail.com
Author: Alexander Pyhalov <a.pyhalov@postgrespro.ru>
Reviewed-by: Alexander Korotkov <aekorotkov@gmail.com>
Backpatch-through: 17
---
 .../postgres_fdw/expected/postgres_fdw.out    | 38 +++++++++++++++++++
 contrib/postgres_fdw/postgres_fdw.c           | 22 +++++++++--
 contrib/postgres_fdw/sql/postgres_fdw.sql     | 17 +++++++++
 3 files changed, 73 insertions(+), 4 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index bb4ed3059c4..d1acee5a5fa 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -4936,6 +4936,44 @@ SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
 ----+----+----+----+----+----+----+----+----+----+----
 (0 rows)
 
+-- Semi-join conditions shouldn't pop up as left/right join clauses.
+SET enable_material TO off;
+EXPLAIN (verbose, costs off)
+SELECT x1.c1 FROM
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x1
+	RIGHT JOIN
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x2
+	ON (x1.c1 = x2.c1)
+ORDER BY x1.c1 LIMIT 10;
+                                                                                                                                                                                 QUERY PLAN                                                                                                                                                                                 
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1
+   Relations: ((public.ft2 ft2_1) LEFT JOIN ((public.ft2) SEMI JOIN (public.ft4))) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT s9.c1 FROM ("S 1"."T 1" r6 LEFT JOIN (SELECT r4."C 1" FROM "S 1"."T 1" r4 WHERE ((r4.c2 < 10)) AND EXISTS (SELECT NULL FROM "S 1"."T 3" r5 WHERE ((r4."C 1" = r5.c1)))) s9(c1) ON (((s9.c1 = r6."C 1")))) WHERE ((r6.c2 < 10)) AND EXISTS (SELECT NULL FROM "S 1"."T 3" r7 WHERE ((r6."C 1" = r7.c1))) ORDER BY s9.c1 ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT x1.c1 FROM
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x1
+	RIGHT JOIN
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x2
+	ON (x1.c1 = x2.c1)
+ORDER BY x1.c1 LIMIT 10;
+ c1 
+----
+  2
+  4
+  6
+  8
+ 10
+ 12
+ 14
+ 16
+ 18
+ 20
+(10 rows)
+
+RESET enable_material;
 -- Can't push down semi-join with inner rel vars in targetlist
 EXPLAIN (verbose, costs off)
 SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 6beae0fa37f..f9bc7b60939 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -5963,16 +5963,30 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 			break;
 
 		case JOIN_LEFT:
-			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+			/*
+			 * When semi-join is involved in the inner or outer part of the
+			 * left join, it's deparsed as a subquery, and we can't refer to
+			 * its vars on the upper level.
+			 */
+			if (fpinfo_i->jointype != JOIN_SEMI)
+				fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
 											  fpinfo_i->remote_conds);
-			fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
+			if (fpinfo_o->jointype != JOIN_SEMI)
+				fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
 											   fpinfo_o->remote_conds);
 			break;
 
 		case JOIN_RIGHT:
-			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+			/*
+			 * When semi-join is involved in the inner or outer part of the
+			 * right join, it's deparsed as a subquery, and we can't refer to
+			 * its vars on the upper level.
+			 */
+			if (fpinfo_o->jointype != JOIN_SEMI)
+				fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
 											  fpinfo_o->remote_conds);
-			fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
+			if (fpinfo_i->jointype != JOIN_SEMI)
+				fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
 											   fpinfo_i->remote_conds);
 			break;
 
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index d45e9f8ab52..ea6287b03fd 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -1455,6 +1455,23 @@ SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
 	WHERE ft2.c1 > 900
 	ORDER BY ft2.c1 LIMIT 10;
 
+-- Semi-join conditions shouldn't pop up as left/right join clauses.
+SET enable_material TO off;
+EXPLAIN (verbose, costs off)
+SELECT x1.c1 FROM
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x1
+	RIGHT JOIN
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x2
+	ON (x1.c1 = x2.c1)
+ORDER BY x1.c1 LIMIT 10;
+SELECT x1.c1 FROM
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x1
+	RIGHT JOIN
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x2
+	ON (x1.c1 = x2.c1)
+ORDER BY x1.c1 LIMIT 10;
+RESET enable_material;
+
 -- Can't push down semi-join with inner rel vars in targetlist
 EXPLAIN (verbose, costs off)
 SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
-- 
2.39.5 (Apple Git-154)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index bb4ed3059c4..d1acee5a5fa 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -4936,6 +4936,44 @@ SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
 ----+----+----+----+----+----+----+----+----+----+----
 (0 rows)
 
+-- Semi-join conditions shouldn't pop up as left/right join clauses.
+SET enable_material TO off;
+EXPLAIN (verbose, costs off)
+SELECT x1.c1 FROM
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x1
+	RIGHT JOIN
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x2
+	ON (x1.c1 = x2.c1)
+ORDER BY x1.c1 LIMIT 10;
+                                                                                                                                                                                 QUERY PLAN                                                                                                                                                                                 
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: ft2.c1
+   Relations: ((public.ft2 ft2_1) LEFT JOIN ((public.ft2) SEMI JOIN (public.ft4))) SEMI JOIN (public.ft4 ft4_1)
+   Remote SQL: SELECT s9.c1 FROM ("S 1"."T 1" r6 LEFT JOIN (SELECT r4."C 1" FROM "S 1"."T 1" r4 WHERE ((r4.c2 < 10)) AND EXISTS (SELECT NULL FROM "S 1"."T 3" r5 WHERE ((r4."C 1" = r5.c1)))) s9(c1) ON (((s9.c1 = r6."C 1")))) WHERE ((r6.c2 < 10)) AND EXISTS (SELECT NULL FROM "S 1"."T 3" r7 WHERE ((r6."C 1" = r7.c1))) ORDER BY s9.c1 ASC NULLS LAST LIMIT 10::bigint
+(4 rows)
+
+SELECT x1.c1 FROM
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x1
+	RIGHT JOIN
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x2
+	ON (x1.c1 = x2.c1)
+ORDER BY x1.c1 LIMIT 10;
+ c1 
+----
+  2
+  4
+  6
+  8
+ 10
+ 12
+ 14
+ 16
+ 18
+ 20
+(10 rows)
+
+RESET enable_material;
 -- Can't push down semi-join with inner rel vars in targetlist
 EXPLAIN (verbose, costs off)
 SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 1131a8bf77e..455ddf101b4 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -5964,16 +5964,30 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 			break;
 
 		case JOIN_LEFT:
-			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+			/*
+			 * When semi-join is involved in the inner or outer part of the
+			 * left join, it's deparsed as a subquery, and we can't refer to
+			 * its vars on the upper level.
+			 */
+			if (fpinfo_i->jointype != JOIN_SEMI)
+				fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
 											  fpinfo_i->remote_conds);
-			fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
+			if (fpinfo_o->jointype != JOIN_SEMI)
+				fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
 											   fpinfo_o->remote_conds);
 			break;
 
 		case JOIN_RIGHT:
-			fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
+			/*
+			 * When semi-join is involved in the inner or outer part of the
+			 * right join, it's deparsed as a subquery, and we can't refer to
+			 * its vars on the upper level.
+			 */
+			if (fpinfo_o->jointype != JOIN_SEMI)
+				fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
 											  fpinfo_o->remote_conds);
-			fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
+			if (fpinfo_i->jointype != JOIN_SEMI)
+				fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
 											   fpinfo_i->remote_conds);
 			break;
 
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index d45e9f8ab52..c58e8fc9912 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -1455,6 +1455,34 @@ SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
 	WHERE ft2.c1 > 900
 	ORDER BY ft2.c1 LIMIT 10;
 
+-- Semi-join conditions shouldn't pop up as left/right join clauses.
+SET enable_material TO off;
+EXPLAIN (verbose, costs off)
+SELECT x1.c1 FROM
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x1
+	RIGHT JOIN
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x2
+	ON (x1.c1 = x2.c1)
+ORDER BY x1.c1 LIMIT 10;
+SELECT x1.c1 FROM
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x1
+	RIGHT JOIN
+		(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x2
+	ON (x1.c1 = x2.c1)
+ORDER BY x1.c1 LIMIT 10;
+
+EXPLAIN (verbose, costs off)
+SELECT x1.c1 FROM
+	(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x1
+        RIGHT JOIN
+                (SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x2
+        ON (x1.c1 = x2.c1)
+        LEFT JOIN
+                (SELECT * FROM ft2 WHERE c2 < 11) x3
+        ON (x1.c1 = x3.c1)
+ORDER BY x1.c1 LIMIT 10;
+RESET enable_material;
+
 -- Can't push down semi-join with inner rel vars in targetlist
 EXPLAIN (verbose, costs off)
 SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE