Re: Implement <null treatment> for window functions

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 7d06b979eb..e69977de76 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -19722,6 +19722,14 @@ SELECT count(*) FROM sometable;
    about frame specifications.
   </para>
 
+  <para>
+   The functions <function>lead</function>, <function>lag</function>,
+   <function>first_value</function>, <function>last_value</function>, and
+   <function>nth_value</function> accept a null treatment option which is
+   <literal>RESPECT NULLS</literal> or <literal>IGNORE NULLS</literal>.
+   If this option is not specified, the default is <literal>RESPECT NULLS</literal>.
+  </para>
+
   <para>
    When an aggregate function is used as a window function, it aggregates
    over the rows within the current row's window frame.
@@ -19735,14 +19743,9 @@ SELECT count(*) FROM sometable;
 
   <note>
    <para>
-    The SQL standard defines a <literal>RESPECT NULLS</literal> or
-    <literal>IGNORE NULLS</literal> option for <function>lead</function>, <function>lag</function>,
-    <function>first_value</function>, <function>last_value</function>, and
-    <function>nth_value</function>.  This is not implemented in
-    <productname>PostgreSQL</productname>: the behavior is always the
-    same as the standard's default, namely <literal>RESPECT NULLS</literal>.
-    Likewise, the standard's <literal>FROM FIRST</literal> or <literal>FROM LAST</literal>
-    option for <function>nth_value</function> is not implemented: only the
+    The SQL standard defines a <literal>FROM FIRST</literal> or <literal>FROM LAST</literal>
+    option for <function>nth_value</function>.  This is not implemented in
+    <productname>PostgreSQL</productname>: only the
     default <literal>FROM FIRST</literal> behavior is supported.  (You can achieve
     the result of <literal>FROM LAST</literal> by reversing the <literal>ORDER BY</literal>
     ordering.)
diff --git a/doc/src/sgml/ref/create_function.sgml b/doc/src/sgml/ref/create_function.sgml
index 3c1eaea651..31e08c26b4 100644
--- a/doc/src/sgml/ref/create_function.sgml
+++ b/doc/src/sgml/ref/create_function.sgml
@@ -28,6 +28,7 @@ CREATE [ OR REPLACE ] FUNCTION
   { LANGUAGE <replaceable class="parameter">lang_name</replaceable>
     | TRANSFORM { FOR TYPE <replaceable class="parameter">type_name</replaceable> } [, ... ]
     | WINDOW
+    | TREAT NULLS
     | IMMUTABLE | STABLE | VOLATILE | [ NOT ] LEAKPROOF
     | CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
     | [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
@@ -293,6 +294,17 @@ CREATE [ OR REPLACE ] FUNCTION
      </listitem>
     </varlistentry>
 
+    <varlistentry>
+     <term><literal>TREAT NULLS</literal></term>
+
+     <listitem>
+      <para><literal>TREAT NULLS</literal> indicates that the function is able
+      to handle the <literal>RESPECT NULLS</literal> and <literal>IGNORE
+      NULLS</literal> options.  Only window functions may specify this.
+      </para>
+     </listitem>
+    </varlistentry>
+
     <varlistentry>
      <term><literal>IMMUTABLE</literal></term>
      <term><literal>STABLE</literal></term>
diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml
index 3fdd87823e..685454c1ec 100644
--- a/doc/src/sgml/syntax.sgml
+++ b/doc/src/sgml/syntax.sgml
@@ -1770,6 +1770,8 @@ FROM generate_series(1,10) AS s(i);
     The syntax of a window function call is one of the following:
 
 <synopsis>
+<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ RESPECT NULLS | IGNORE NULLS ] OVER <replaceable>window_name</replaceable>
+<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ RESPECT NULLS | IGNORE NULLS ] OVER ( <replaceable class="parameter">window_definition</replaceable> )
 <replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER <replaceable>window_name</replaceable>
 <replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER ( <replaceable class="parameter">window_definition</replaceable> )
 <replaceable>function_name</replaceable> ( * ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER <replaceable>window_name</replaceable>
@@ -1783,6 +1785,18 @@ FROM generate_series(1,10) AS s(i);
 [ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [ NULLS { FIRST | LAST } ] [, ...] ]
 [ <replaceable class="parameter">frame_clause</replaceable> ]
 </synopsis>
+   </para>
+
+   <note>
+    <para>
+     The versions with <literal>RESPECT NULLS</literal> or <literal>IGNORE
+     NULLS</literal> only apply to true window functions, whereas the versions
+     with <literal>FILTER</literal> only apply to aggregate functions used as
+     window functions.
+    </para>
+   </note>
+
+   <para>
     The optional <replaceable class="parameter">frame_clause</replaceable>
     can be one of
 <synopsis>
diff --git a/src/backend/catalog/pg_aggregate.c b/src/backend/catalog/pg_aggregate.c
index 7664bb6285..fea8778ec8 100644
--- a/src/backend/catalog/pg_aggregate.c
+++ b/src/backend/catalog/pg_aggregate.c
@@ -627,6 +627,7 @@ AggregateCreate(const char *aggName,
 									 * definable for agg) */
 							 false, /* isLeakProof */
 							 false, /* isStrict (not needed for agg) */
+							 false, /* null_treatment (not needed for agg) */
 							 PROVOLATILE_IMMUTABLE, /* volatility (not needed
 													 * for agg) */
 							 proparallel,
@@ -848,7 +849,7 @@ lookup_agg_function(List *fnName,
 							   nargs, input_types, false, false,
 							   &fnOid, rettype, &retset,
 							   &nvargs, &vatype,
-							   &true_oid_array, NULL);
+							   &true_oid_array, NULL, NULL);
 
 	/* only valid case is a normal function not returning a set */
 	if (fdresult != FUNCDETAIL_NORMAL || !OidIsValid(fnOid))
diff --git a/src/backend/catalog/pg_proc.c b/src/backend/catalog/pg_proc.c
index 1dd9ecc063..2783b0d630 100644
--- a/src/backend/catalog/pg_proc.c
+++ b/src/backend/catalog/pg_proc.c
@@ -80,6 +80,7 @@ ProcedureCreate(const char *procedureName,
 				bool security_definer,
 				bool isLeakProof,
 				bool isStrict,
+				bool null_treatment,
 				char volatility,
 				char parallel,
 				oidvector *parameterTypes,
@@ -307,6 +308,7 @@ ProcedureCreate(const char *procedureName,
 	values[Anum_pg_proc_prosecdef - 1] = BoolGetDatum(security_definer);
 	values[Anum_pg_proc_proleakproof - 1] = BoolGetDatum(isLeakProof);
 	values[Anum_pg_proc_proisstrict - 1] = BoolGetDatum(isStrict);
+	values[Anum_pg_proc_pronulltreatment - 1] = BoolGetDatum(null_treatment);
 	values[Anum_pg_proc_proretset - 1] = BoolGetDatum(returnsSet);
 	values[Anum_pg_proc_provolatile - 1] = CharGetDatum(volatility);
 	values[Anum_pg_proc_proparallel - 1] = CharGetDatum(parallel);
@@ -386,6 +388,12 @@ ProcedureCreate(const char *procedureName,
 					  errdetail("\"%s\" is a window function.", procedureName) :
 					  0)));
 
+		/* Not okay to set null treatment if not a window function */
+		if (null_treatment && oldproc->prokind != PROKIND_WINDOW)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+					 errmsg("cannot set null treatment on a non-window function")));
+
 		dropcmd = (prokind == PROKIND_PROCEDURE ? "DROP PROCEDURE" :
 				   prokind == PROKIND_AGGREGATE ? "DROP AGGREGATE" :
 				   "DROP FUNCTION");
diff --git a/src/backend/catalog/sql_features.txt b/src/backend/catalog/sql_features.txt
index caa971c435..0615b08858 100644
--- a/src/backend/catalog/sql_features.txt
+++ b/src/backend/catalog/sql_features.txt
@@ -508,9 +508,9 @@ T612	Advanced OLAP operations			YES
 T613	Sampling			YES	
 T614	NTILE function			YES	
 T615	LEAD and LAG functions			YES	
-T616	Null treatment option for LEAD and LAG functions			NO	
+T616	Null treatment option for LEAD and LAG functions			YES	
 T617	FIRST_VALUE and LAST_VALUE function			YES	
-T618	NTH_VALUE function			NO	function exists, but some options missing
+T618	NTH_VALUE function			NO	supported except FROM LAST is not implemented
 T619	Nested window functions			NO	
 T620	WINDOW clause: GROUPS option			YES	
 T621	Enhanced numeric functions			YES	
diff --git a/src/backend/commands/functioncmds.c b/src/backend/commands/functioncmds.c
index c3ce480c8f..245a768463 100644
--- a/src/backend/commands/functioncmds.c
+++ b/src/backend/commands/functioncmds.c
@@ -697,6 +697,7 @@ compute_function_attributes(ParseState *pstate,
 							bool *windowfunc_p,
 							char *volatility_p,
 							bool *strict_p,
+							bool *null_treatment_p,
 							bool *security_definer,
 							bool *leakproof_p,
 							ArrayType **proconfig,
@@ -710,6 +711,7 @@ compute_function_attributes(ParseState *pstate,
 	DefElem    *language_item = NULL;
 	DefElem    *transform_item = NULL;
 	DefElem    *windowfunc_item = NULL;
+	DefElem    *nulltreatment_item = NULL;
 	DefElem    *volatility_item = NULL;
 	DefElem    *strict_item = NULL;
 	DefElem    *security_item = NULL;
@@ -765,6 +767,20 @@ compute_function_attributes(ParseState *pstate,
 						 parser_errposition(pstate, defel->location)));
 			windowfunc_item = defel;
 		}
+		else if (strcmp(defel->defname, "null_treatment") == 0)
+		{
+			if (nulltreatment_item)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 parser_errposition(pstate, defel->location)));
+			if (is_procedure)
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+						 errmsg("invalid attribute in procedure definition"),
+						 parser_errposition(pstate, defel->location)));
+			nulltreatment_item = defel;
+		}
 		else if (compute_common_attribute(pstate,
 										  is_procedure,
 										  defel,
@@ -816,6 +832,14 @@ compute_function_attributes(ParseState *pstate,
 		*volatility_p = interpret_func_volatility(volatility_item);
 	if (strict_item)
 		*strict_p = intVal(strict_item->arg);
+	if (nulltreatment_item)
+	{
+		*null_treatment_p = intVal(nulltreatment_item->arg);
+		if (*null_treatment_p && !*windowfunc_p)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+					 errmsg("cannot set null treatment on a non-window function")));
+	}
 	if (security_item)
 		*security_definer = intVal(security_item->arg);
 	if (leakproof_item)
@@ -941,6 +965,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 				isStrict,
 				security,
 				isLeakProof;
+	bool		null_treatment;
 	char		volatility;
 	ArrayType  *proconfig;
 	float4		procost;
@@ -964,6 +989,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 	/* Set default attributes */
 	isWindowFunc = false;
 	isStrict = false;
+	null_treatment = false;
 	security = false;
 	isLeakProof = false;
 	volatility = PROVOLATILE_VOLATILE;
@@ -979,7 +1005,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 								stmt->options,
 								&as_clause, &language, &transformDefElem,
 								&isWindowFunc, &volatility,
-								&isStrict, &security, &isLeakProof,
+								&isStrict, &null_treatment, &security, &isLeakProof,
 								&proconfig, &procost, &prorows,
 								&prosupport, &parallel);
 
@@ -1159,6 +1185,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 						   security,
 						   isLeakProof,
 						   isStrict,
+						   null_treatment,
 						   volatility,
 						   parallel,
 						   parameterTypes,
diff --git a/src/backend/commands/typecmds.c b/src/backend/commands/typecmds.c
index 483bb65ddc..003a3434e3 100644
--- a/src/backend/commands/typecmds.c
+++ b/src/backend/commands/typecmds.c
@@ -1592,6 +1592,7 @@ makeRangeConstructors(const char *name, Oid namespace,
 								 false, /* security_definer */
 								 false, /* leakproof */
 								 false, /* isStrict */
+								 false, /* null_treatment */
 								 PROVOLATILE_IMMUTABLE, /* volatility */
 								 PROPARALLEL_SAFE,	/* parallel safety */
 								 constructorArgTypesVector, /* parameterTypes */
diff --git a/src/backend/executor/nodeWindowAgg.c b/src/backend/executor/nodeWindowAgg.c
index de58df3d3f..832b40b849 100644
--- a/src/backend/executor/nodeWindowAgg.c
+++ b/src/backend/executor/nodeWindowAgg.c
@@ -68,6 +68,7 @@ typedef struct WindowObjectData
 	int			readptr;		/* tuplestore read pointer for this fn */
 	int64		markpos;		/* row that markptr is positioned on */
 	int64		seekpos;		/* row that readptr is positioned on */
+	NullTreatment	null_treatment;	/* RESPECT/IGNORE NULLS? */
 } WindowObjectData;
 
 /*
@@ -2473,6 +2474,7 @@ ExecInitWindowAgg(WindowAgg *node, EState *estate, int eflags)
 			winobj->winstate = winstate;
 			winobj->argstates = wfuncstate->args;
 			winobj->localmem = NULL;
+			winobj->null_treatment = wfunc->winnulltreatment;
 			perfuncstate->winobj = winobj;
 
 			/* It's a real window function, so set up to call it. */
@@ -3173,48 +3175,103 @@ WinGetFuncArgInPartition(WindowObject winobj, int argno,
 	TupleTableSlot *slot;
 	bool		gottuple;
 	int64		abs_pos;
+	bool		ignore_nulls = false;
+	int			target = relpos;
+	int			step;
+	Datum		result;
 
 	Assert(WindowObjectIsValid(winobj));
 	winstate = winobj->winstate;
 	econtext = winstate->ss.ps.ps_ExprContext;
 	slot = winstate->temp_slot_1;
 
-	switch (seektype)
+	/*
+	 * If we're not ignoring nulls, we'll just go straight to the desired row.
+	 * But if we are ignoring nulls, we'll have to step towards the target row
+	 * by row so we need to determine how we get there.
+	 */
+	if (winobj->null_treatment == NULL_TREATMENT_IGNORE)
 	{
-		case WINDOW_SEEK_CURRENT:
-			abs_pos = winstate->currentpos + relpos;
-			break;
-		case WINDOW_SEEK_HEAD:
-			abs_pos = relpos;
-			break;
-		case WINDOW_SEEK_TAIL:
-			spool_tuples(winstate, -1);
-			abs_pos = winstate->spooled_rows - 1 + relpos;
-			break;
-		default:
-			elog(ERROR, "unrecognized window seek type: %d", seektype);
-			abs_pos = 0;		/* keep compiler quiet */
-			break;
-	}
-
-	gottuple = window_gettupleslot(winobj, abs_pos, slot);
+		ignore_nulls = true;
 
-	if (!gottuple)
-	{
-		if (isout)
-			*isout = true;
-		*isnull = true;
-		return (Datum) 0;
+		if (seektype == WINDOW_SEEK_HEAD)
+		{
+			step = 1;
+			relpos = 0;
+		}
+		else if (seektype == WINDOW_SEEK_TAIL)
+		{
+			step = -1;
+			relpos = 0;
+		}
+		else
+		{
+			if (target > 0)
+				step = 1;
+			else if (target < 0)
+				step = -1;
+			else
+				step = 0;
+			relpos = step;
+		}
 	}
-	else
+
+	for (;;)
 	{
-		if (isout)
-			*isout = false;
-		if (set_mark)
-			WinSetMarkPosition(winobj, abs_pos);
+		switch (seektype)
+		{
+			case WINDOW_SEEK_CURRENT:
+				abs_pos = winstate->currentpos + relpos;
+				break;
+			case WINDOW_SEEK_HEAD:
+				abs_pos = relpos;
+				break;
+			case WINDOW_SEEK_TAIL:
+				spool_tuples(winstate, -1);
+				abs_pos = winstate->spooled_rows - 1 + relpos;
+				break;
+			default:
+				elog(ERROR, "unrecognized window seek type: %d", seektype);
+				abs_pos = 0;		/* keep compiler quiet */
+				break;
+		}
+
+		gottuple = window_gettupleslot(winobj, abs_pos, slot);
+
+		/* Did we fall off the end of the partition? */
+		if (!gottuple)
+		{
+			if (isout)
+				*isout = true;
+			*isnull = true;
+			return (Datum) 0;
+		}
+
+		/* Evaluate the expression at this row */
 		econtext->ecxt_outertuple = slot;
-		return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
-							econtext, isnull);
+		result = ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
+							  econtext, isnull);
+
+		/* If we got a null and we're ignoring them, move the goalposts */
+		if (ignore_nulls && *isnull)
+			target += step;
+
+		/* Once we've reached our target, we're done */
+		if (relpos == target)
+		{
+			if (isout)
+				*isout = false;
+			/*
+			 * We can only mark the row if we're not ignoring nulls (because we
+			 * jump straight there).
+			 */
+			if (set_mark && !ignore_nulls)
+				WinSetMarkPosition(winobj, abs_pos);
+			return result;
+		}
+
+		/* Otherwise move closer and try again */
+		relpos += step;
 	}
 }
 
@@ -3261,170 +3318,218 @@ WinGetFuncArgInFrame(WindowObject winobj, int argno,
 	TupleTableSlot *slot;
 	int64		abs_pos;
 	int64		mark_pos;
+	bool		ignore_nulls = false;
+	int			target = relpos;
+	int			step;
+	Datum		result;
 
 	Assert(WindowObjectIsValid(winobj));
 	winstate = winobj->winstate;
 	econtext = winstate->ss.ps.ps_ExprContext;
 	slot = winstate->temp_slot_1;
 
-	switch (seektype)
+	/*
+	 * If we're not ignoring nulls, we'll just go straight to the desired row.
+	 * But if we are ignoring nulls, we'll have to step towards the target row
+	 * by row so we need to determine how we get there.
+	 */
+	if (winobj->null_treatment == NULL_TREATMENT_IGNORE)
 	{
-		case WINDOW_SEEK_CURRENT:
-			elog(ERROR, "WINDOW_SEEK_CURRENT is not supported for WinGetFuncArgInFrame");
-			abs_pos = mark_pos = 0; /* keep compiler quiet */
-			break;
-		case WINDOW_SEEK_HEAD:
-			/* rejecting relpos < 0 is easy and simplifies code below */
-			if (relpos < 0)
-				goto out_of_frame;
-			update_frameheadpos(winstate);
-			abs_pos = winstate->frameheadpos + relpos;
-			mark_pos = abs_pos;
+		ignore_nulls = true;
 
-			/*
-			 * Account for exclusion option if one is active, but advance only
-			 * abs_pos not mark_pos.  This prevents changes of the current
-			 * row's peer group from resulting in trying to fetch a row before
-			 * some previous mark position.
-			 *
-			 * Note that in some corner cases such as current row being
-			 * outside frame, these calculations are theoretically too simple,
-			 * but it doesn't matter because we'll end up deciding the row is
-			 * out of frame.  We do not attempt to avoid fetching rows past
-			 * end of frame; that would happen in some cases anyway.
-			 */
-			switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
-			{
-				case 0:
-					/* no adjustment needed */
-					break;
-				case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
-					if (abs_pos >= winstate->currentpos &&
-						winstate->currentpos >= winstate->frameheadpos)
-						abs_pos++;
-					break;
-				case FRAMEOPTION_EXCLUDE_GROUP:
-					update_grouptailpos(winstate);
-					if (abs_pos >= winstate->groupheadpos &&
-						winstate->grouptailpos > winstate->frameheadpos)
-					{
-						int64		overlapstart = Max(winstate->groupheadpos,
-													   winstate->frameheadpos);
+		if (target > 0)
+			step = 1;
+		else if (target < 0)
+			step = -1;
+		else if (seektype == WINDOW_SEEK_HEAD)
+			step = 1;
+		else if (seektype == WINDOW_SEEK_TAIL)
+			step = -1;
+		else
+			step = 0;
 
-						abs_pos += winstate->grouptailpos - overlapstart;
-					}
-					break;
-				case FRAMEOPTION_EXCLUDE_TIES:
-					update_grouptailpos(winstate);
-					if (abs_pos >= winstate->groupheadpos &&
-						winstate->grouptailpos > winstate->frameheadpos)
-					{
-						int64		overlapstart = Max(winstate->groupheadpos,
-													   winstate->frameheadpos);
+		relpos = 0;
+	}
 
-						if (abs_pos == overlapstart)
-							abs_pos = winstate->currentpos;
-						else
-							abs_pos += winstate->grouptailpos - overlapstart - 1;
-					}
-					break;
-				default:
-					elog(ERROR, "unrecognized frame option state: 0x%x",
-						 winstate->frameOptions);
-					break;
-			}
-			break;
-		case WINDOW_SEEK_TAIL:
-			/* rejecting relpos > 0 is easy and simplifies code below */
-			if (relpos > 0)
-				goto out_of_frame;
-			update_frametailpos(winstate);
-			abs_pos = winstate->frametailpos - 1 + relpos;
+	for (;;)
+	{
+		switch (seektype)
+		{
+			case WINDOW_SEEK_CURRENT:
+				elog(ERROR, "WINDOW_SEEK_CURRENT is not supported for WinGetFuncArgInFrame");
+				abs_pos = mark_pos = 0; /* keep compiler quiet */
+				break;
+			case WINDOW_SEEK_HEAD:
+				/* rejecting relpos < 0 is easy and simplifies code below */
+				if (relpos < 0)
+					goto out_of_frame;
+				update_frameheadpos(winstate);
+				abs_pos = winstate->frameheadpos + relpos;
+				mark_pos = abs_pos;
 
-			/*
-			 * Account for exclusion option if one is active.  If there is no
-			 * exclusion, we can safely set the mark at the accessed row.  But
-			 * if there is, we can only mark the frame start, because we can't
-			 * be sure how far back in the frame the exclusion might cause us
-			 * to fetch in future.  Furthermore, we have to actually check
-			 * against frameheadpos here, since it's unsafe to try to fetch a
-			 * row before frame start if the mark might be there already.
-			 */
-			switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
-			{
-				case 0:
-					/* no adjustment needed */
-					mark_pos = abs_pos;
-					break;
-				case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
-					if (abs_pos <= winstate->currentpos &&
-						winstate->currentpos < winstate->frametailpos)
-						abs_pos--;
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				case FRAMEOPTION_EXCLUDE_GROUP:
-					update_grouptailpos(winstate);
-					if (abs_pos < winstate->grouptailpos &&
-						winstate->groupheadpos < winstate->frametailpos)
-					{
-						int64		overlapend = Min(winstate->grouptailpos,
-													 winstate->frametailpos);
+				/*
+				 * Account for exclusion option if one is active, but advance only
+				 * abs_pos not mark_pos.  This prevents changes of the current
+				 * row's peer group from resulting in trying to fetch a row before
+				 * some previous mark position.
+				 *
+				 * Note that in some corner cases such as current row being
+				 * outside frame, these calculations are theoretically too simple,
+				 * but it doesn't matter because we'll end up deciding the row is
+				 * out of frame.  We do not attempt to avoid fetching rows past
+				 * end of frame; that would happen in some cases anyway.
+				 */
+				switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
+				{
+					case 0:
+						/* no adjustment needed */
+						break;
+					case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
+						if (abs_pos >= winstate->currentpos &&
+							winstate->currentpos >= winstate->frameheadpos)
+							abs_pos++;
+						break;
+					case FRAMEOPTION_EXCLUDE_GROUP:
+						update_grouptailpos(winstate);
+						if (abs_pos >= winstate->groupheadpos &&
+							winstate->grouptailpos > winstate->frameheadpos)
+						{
+							int64		overlapstart = Max(winstate->groupheadpos,
+														   winstate->frameheadpos);
+
+							abs_pos += winstate->grouptailpos - overlapstart;
+						}
+						break;
+					case FRAMEOPTION_EXCLUDE_TIES:
+						update_grouptailpos(winstate);
+						if (abs_pos >= winstate->groupheadpos &&
+							winstate->grouptailpos > winstate->frameheadpos)
+						{
+							int64		overlapstart = Max(winstate->groupheadpos,
+														   winstate->frameheadpos);
+
+							if (abs_pos == overlapstart)
+								abs_pos = winstate->currentpos;
+							else
+								abs_pos += winstate->grouptailpos - overlapstart - 1;
+						}
+						break;
+					default:
+						elog(ERROR, "unrecognized frame option state: 0x%x",
+							 winstate->frameOptions);
+						break;
+				}
+				break;
+			case WINDOW_SEEK_TAIL:
+				/* rejecting relpos > 0 is easy and simplifies code below */
+				if (relpos > 0)
+					goto out_of_frame;
+				update_frametailpos(winstate);
+				abs_pos = winstate->frametailpos - 1 + relpos;
 
-						abs_pos -= overlapend - winstate->groupheadpos;
-					}
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				case FRAMEOPTION_EXCLUDE_TIES:
-					update_grouptailpos(winstate);
-					if (abs_pos < winstate->grouptailpos &&
-						winstate->groupheadpos < winstate->frametailpos)
-					{
-						int64		overlapend = Min(winstate->grouptailpos,
-													 winstate->frametailpos);
+				/*
+				 * Account for exclusion option if one is active.  If there is no
+				 * exclusion, we can safely set the mark at the accessed row.  But
+				 * if there is, we can only mark the frame start, because we can't
+				 * be sure how far back in the frame the exclusion might cause us
+				 * to fetch in future.  Furthermore, we have to actually check
+				 * against frameheadpos here, since it's unsafe to try to fetch a
+				 * row before frame start if the mark might be there already.
+				 */
+				switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
+				{
+					case 0:
+						/* no adjustment needed */
+						mark_pos = abs_pos;
+						break;
+					case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
+						if (abs_pos <= winstate->currentpos &&
+							winstate->currentpos < winstate->frametailpos)
+							abs_pos--;
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					case FRAMEOPTION_EXCLUDE_GROUP:
+						update_grouptailpos(winstate);
+						if (abs_pos < winstate->grouptailpos &&
+							winstate->groupheadpos < winstate->frametailpos)
+						{
+							int64		overlapend = Min(winstate->grouptailpos,
+														 winstate->frametailpos);
+
+							abs_pos -= overlapend - winstate->groupheadpos;
+						}
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					case FRAMEOPTION_EXCLUDE_TIES:
+						update_grouptailpos(winstate);
+						if (abs_pos < winstate->grouptailpos &&
+							winstate->groupheadpos < winstate->frametailpos)
+						{
+							int64		overlapend = Min(winstate->grouptailpos,
+														 winstate->frametailpos);
+
+							if (abs_pos == overlapend - 1)
+								abs_pos = winstate->currentpos;
+							else
+								abs_pos -= overlapend - 1 - winstate->groupheadpos;
+						}
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					default:
+						elog(ERROR, "unrecognized frame option state: 0x%x",
+							 winstate->frameOptions);
+						mark_pos = 0;	/* keep compiler quiet */
+						break;
+				}
+				break;
+			default:
+				elog(ERROR, "unrecognized window seek type: %d", seektype);
+				abs_pos = mark_pos = 0; /* keep compiler quiet */
+				break;
+		}
 
-						if (abs_pos == overlapend - 1)
-							abs_pos = winstate->currentpos;
-						else
-							abs_pos -= overlapend - 1 - winstate->groupheadpos;
-					}
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				default:
-					elog(ERROR, "unrecognized frame option state: 0x%x",
-						 winstate->frameOptions);
-					mark_pos = 0;	/* keep compiler quiet */
-					break;
-			}
-			break;
-		default:
-			elog(ERROR, "unrecognized window seek type: %d", seektype);
-			abs_pos = mark_pos = 0; /* keep compiler quiet */
-			break;
-	}
+		if (!window_gettupleslot(winobj, abs_pos, slot))
+			goto out_of_frame;
 
-	if (!window_gettupleslot(winobj, abs_pos, slot))
-		goto out_of_frame;
+		/* The code above does not detect all out-of-frame cases, so check */
+		if (row_is_in_frame(winstate, abs_pos, slot) <= 0)
+			goto out_of_frame;
 
-	/* The code above does not detect all out-of-frame cases, so check */
-	if (row_is_in_frame(winstate, abs_pos, slot) <= 0)
-		goto out_of_frame;
+		/* Evaluate the expression at this row */
+		econtext->ecxt_outertuple = slot;
+		result = ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
+							  econtext, isnull);
 
-	if (isout)
-		*isout = false;
-	if (set_mark)
-		WinSetMarkPosition(winobj, mark_pos);
-	econtext->ecxt_outertuple = slot;
-	return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
-						econtext, isnull);
+		/* If we got a null and we're ignoring them, move the goalposts */
+		if (ignore_nulls && *isnull)
+			target += step;
+
+		/* Once we've reached our target, we're done */
+		if (relpos == target)
+		{
+			if (isout)
+				*isout = false;
+			/*
+			 * We can only mark the row if we're not ignoring nulls (because we
+			 * jump straight there).
+			 */
+			if (set_mark && !ignore_nulls)
+				WinSetMarkPosition(winobj, mark_pos);
+			return result;
+		}
+
+		/* Otherwise move closer and try again */
+		relpos += step;
+	}
 
 out_of_frame:
 	if (isout)
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 5a591d0a75..29bb505504 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -1531,6 +1531,7 @@ _copyWindowFunc(const WindowFunc *from)
 	COPY_SCALAR_FIELD(winref);
 	COPY_SCALAR_FIELD(winstar);
 	COPY_SCALAR_FIELD(winagg);
+	COPY_SCALAR_FIELD(winnulltreatment);
 	COPY_LOCATION_FIELD(location);
 
 	return newnode;
@@ -2688,6 +2689,7 @@ _copyFuncCall(const FuncCall *from)
 	COPY_SCALAR_FIELD(agg_distinct);
 	COPY_SCALAR_FIELD(func_variadic);
 	COPY_SCALAR_FIELD(funcformat);
+	COPY_SCALAR_FIELD(win_null_treatment);
 	COPY_LOCATION_FIELD(location);
 
 	return newnode;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index e2895a8985..b1267e8da5 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -264,6 +264,7 @@ _equalWindowFunc(const WindowFunc *a, const WindowFunc *b)
 	COMPARE_SCALAR_FIELD(winref);
 	COMPARE_SCALAR_FIELD(winstar);
 	COMPARE_SCALAR_FIELD(winagg);
+	COMPARE_SCALAR_FIELD(winnulltreatment);
 	COMPARE_LOCATION_FIELD(location);
 
 	return true;
@@ -2376,6 +2377,7 @@ _equalFuncCall(const FuncCall *a, const FuncCall *b)
 	COMPARE_SCALAR_FIELD(agg_distinct);
 	COMPARE_SCALAR_FIELD(func_variadic);
 	COMPARE_SCALAR_FIELD(funcformat);
+	COMPARE_SCALAR_FIELD(win_null_treatment);
 	COMPARE_LOCATION_FIELD(location);
 
 	return true;
diff --git a/src/backend/nodes/makefuncs.c b/src/backend/nodes/makefuncs.c
index ee033ae779..587cd43e6b 100644
--- a/src/backend/nodes/makefuncs.c
+++ b/src/backend/nodes/makefuncs.c
@@ -596,6 +596,7 @@ makeFuncCall(List *name, List *args, CoercionForm funcformat, int location)
 	n->agg_distinct = false;
 	n->func_variadic = false;
 	n->funcformat = funcformat;
+	n->win_null_treatment = NULL_TREATMENT_NONE;
 	n->location = location;
 	return n;
 }
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index f26498cea2..0646356ccd 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -1182,6 +1182,7 @@ _outWindowFunc(StringInfo str, const WindowFunc *node)
 	WRITE_UINT_FIELD(winref);
 	WRITE_BOOL_FIELD(winstar);
 	WRITE_BOOL_FIELD(winagg);
+	WRITE_INT_FIELD(winnulltreatment);
 	WRITE_LOCATION_FIELD(location);
 }
 
@@ -2771,6 +2772,7 @@ _outFuncCall(StringInfo str, const FuncCall *node)
 	WRITE_BOOL_FIELD(agg_distinct);
 	WRITE_BOOL_FIELD(func_variadic);
 	WRITE_ENUM_FIELD(funcformat, CoercionForm);
+	WRITE_BOOL_FIELD(win_null_treatment);
 	WRITE_LOCATION_FIELD(location);
 }
 
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index ab7b535caa..95d7f04413 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -654,6 +654,7 @@ _readWindowFunc(void)
 	READ_UINT_FIELD(winref);
 	READ_BOOL_FIELD(winstar);
 	READ_BOOL_FIELD(winagg);
+	READ_INT_FIELD(winnulltreatment);
 	READ_LOCATION_FIELD(location);
 
 	READ_DONE();
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 85ef873caa..ebcc3a1c13 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -2486,6 +2486,7 @@ eval_const_expressions_mutator(Node *node,
 				newexpr->winref = expr->winref;
 				newexpr->winstar = expr->winstar;
 				newexpr->winagg = expr->winagg;
+				newexpr->winnulltreatment = expr->winnulltreatment;
 				newexpr->location = expr->location;
 
 				return (Node *) newexpr;
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index efc9c99754..ffb758bb31 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -590,6 +590,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <list>	window_clause window_definition_list opt_partition_clause
 %type <windef>	window_definition over_clause window_specification
 				opt_frame_clause frame_extent frame_bound
+%type <ival>	null_treatment
 %type <ival>	opt_window_exclusion_clause
 %type <str>		opt_existing_window_name
 %type <boolean> opt_if_not_exists
@@ -658,7 +659,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 	HANDLER HAVING HEADER_P HOLD HOUR_P
 
-	IDENTITY_P IF_P ILIKE IMMEDIATE IMMUTABLE IMPLICIT_P IMPORT_P IN_P INCLUDE
+	IDENTITY_P IF_P IGNORE_P ILIKE IMMEDIATE IMMUTABLE IMPLICIT_P IMPORT_P IN_P INCLUDE
 	INCLUDING INCREMENT INDEX INDEXES INHERIT INHERITS INITIALLY INLINE_P
 	INNER_P INOUT INPUT_P INSENSITIVE INSERT INSTEAD INT_P INTEGER
 	INTERSECT INTERVAL INTO INVOKER IS ISNULL ISOLATION
@@ -690,7 +691,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 	RANGE READ REAL REASSIGN RECHECK RECURSIVE REF REFERENCES REFERENCING
 	REFRESH REINDEX RELATIVE_P RELEASE RENAME REPEATABLE REPLACE REPLICA
-	RESET RESTART RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROLLUP
+	RESET RESPECT RESTART RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROLLUP
 	ROUTINE ROUTINES ROW ROWS RULE
 
 	SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
@@ -7806,6 +7807,10 @@ createfunc_opt_item:
 				{
 					$$ = makeDefElem("window", (Node *)makeInteger(true), @1);
 				}
+			| TREAT NULLS_P
+				{
+					$$ = makeDefElem("null_treatment", (Node *)makeInteger(true), @1);
+				}
 			| common_func_opt_item
 				{
 					$$ = $1;
@@ -13741,6 +13746,14 @@ func_expr: func_application within_group_clause filter_clause over_clause
 					}
 					n->agg_filter = $3;
 					n->over = $4;
+					n->win_null_treatment = NULL_TREATMENT_NONE;
+					$$ = (Node *) n;
+				}
+			| func_application null_treatment over_clause
+				{
+					FuncCall *n = (FuncCall *) $1;
+					n->over = $3;
+					n->win_null_treatment = $2;
 					$$ = (Node *) n;
 				}
 			| func_expr_common_subexpr
@@ -14161,6 +14174,11 @@ window_definition:
 				}
 		;
 
+null_treatment:
+			IGNORE_P NULLS_P	{ $$ = NULL_TREATMENT_IGNORE; }
+			| RESPECT NULLS_P	{ $$ = NULL_TREATMENT_RESPECT; }
+		;
+
 over_clause: OVER window_specification
 				{ $$ = $2; }
 			| OVER ColId
@@ -15242,6 +15260,7 @@ unreserved_keyword:
 			| HOUR_P
 			| IDENTITY_P
 			| IF_P
+			| IGNORE_P
 			| IMMEDIATE
 			| IMMUTABLE
 			| IMPLICIT_P
@@ -15348,6 +15367,7 @@ unreserved_keyword:
 			| REPLACE
 			| REPLICA
 			| RESET
+			| RESPECT
 			| RESTART
 			| RESTRICT
 			| RETURNS
diff --git a/src/backend/parser/parse_func.c b/src/backend/parser/parse_func.c
index 8b4e3ca5e1..844e8fb79f 100644
--- a/src/backend/parser/parse_func.c
+++ b/src/backend/parser/parse_func.c
@@ -97,6 +97,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 	bool		agg_distinct = (fn ? fn->agg_distinct : false);
 	bool		func_variadic = (fn ? fn->func_variadic : false);
 	CoercionForm funcformat = (fn ? fn->funcformat : COERCE_EXPLICIT_CALL);
+	NullTreatment	win_null_treatment = (fn ? fn->win_null_treatment : NULL_TREATMENT_NONE);
 	bool		could_be_projection;
 	Oid			rettype;
 	Oid			funcid;
@@ -108,6 +109,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 	Oid		   *declared_arg_types;
 	List	   *argnames;
 	List	   *argdefaults;
+	bool		null_treatment;
 	Node	   *retval;
 	bool		retset;
 	int			nvargs;
@@ -267,7 +269,8 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 							   !func_variadic, true,
 							   &funcid, &rettype, &retset,
 							   &nvargs, &vatype,
-							   &declared_arg_types, &argdefaults);
+							   &declared_arg_types, &argdefaults,
+							   &null_treatment);
 
 	cancel_parser_errposition_callback(&pcbstate);
 
@@ -507,6 +510,13 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 						 errmsg("%s is not an ordered-set aggregate, so it cannot have WITHIN GROUP",
 								NameListToString(funcname)),
 						 parser_errposition(pstate, location)));
+
+			/* It also can't treat nulls as a window function */
+			if (over && win_null_treatment != NULL_TREATMENT_NONE)
+				ereport(ERROR,
+						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+						 errmsg("aggregate functions do not accept RESPECT/IGNORE NULLS"),
+						 parser_errposition(pstate, location)));
 		}
 	}
 	else if (fdresult == FUNCDETAIL_WINDOWFUNC)
@@ -527,6 +537,13 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 					 errmsg("window function %s cannot have WITHIN GROUP",
 							NameListToString(funcname)),
 					 parser_errposition(pstate, location)));
+
+		if (!null_treatment && win_null_treatment != NULL_TREATMENT_NONE)
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("window function %s does not accept RESPECT/IGNORE NULLS",
+							NameListToString(funcname)),
+					 parser_errposition(pstate, location)));
 	}
 	else if (fdresult == FUNCDETAIL_COERCION)
 	{
@@ -824,6 +841,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 		wfunc->winstar = agg_star;
 		wfunc->winagg = (fdresult == FUNCDETAIL_AGGREGATE);
 		wfunc->aggfilter = agg_filter;
+		wfunc->winnulltreatment = win_null_treatment;
 		wfunc->location = location;
 
 		/*
@@ -1394,7 +1412,8 @@ func_get_detail(List *funcname,
 				int *nvargs,	/* return value */
 				Oid *vatype,	/* return value */
 				Oid **true_typeids, /* return value */
-				List **argdefaults) /* optional return value */
+				List **argdefaults, /* optional return value */
+				bool *null_treatment) /* optional return value */
 {
 	FuncCandidateList raw_candidates;
 	FuncCandidateList best_candidate;
@@ -1408,6 +1427,8 @@ func_get_detail(List *funcname,
 	*true_typeids = NULL;
 	if (argdefaults)
 		*argdefaults = NIL;
+	if (null_treatment)
+		*null_treatment = NULL_TREATMENT_NONE;
 
 	/* Get list of possible candidates from namespace search */
 	raw_candidates = FuncnameGetCandidates(funcname, nargs, fargnames,
@@ -1685,6 +1706,8 @@ func_get_detail(List *funcname,
 				*argdefaults = defaults;
 			}
 		}
+		if (null_treatment)
+			*null_treatment = pform->pronulltreatment;
 
 		switch (pform->prokind)
 		{
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index c2c6df2a4f..1f44cb54b5 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -2661,6 +2661,9 @@ pg_get_functiondef(PG_FUNCTION_ARGS)
 
 	if (proc->prokind == PROKIND_WINDOW)
 		appendStringInfoString(&buf, " WINDOW");
+	if (proc->pronulltreatment)
+		appendStringInfoString(&buf, " TREAT NULLS");
+
 	switch (proc->provolatile)
 	{
 		case PROVOLATILE_IMMUTABLE:
@@ -9475,7 +9478,12 @@ get_windowfunc_expr(WindowFunc *wfunc, deparse_context *context)
 		get_rule_expr((Node *) wfunc->aggfilter, context, false);
 	}
 
-	appendStringInfoString(buf, ") OVER ");
+	if (wfunc->winnulltreatment == NULL_TREATMENT_IGNORE)
+		appendStringInfoString(buf, ") IGNORE NULLS OVER ");
+	else if (wfunc->winnulltreatment == NULL_TREATMENT_RESPECT)
+		appendStringInfoString(buf, ") RESPECT NULLS OVER ");
+	else
+		appendStringInfoString(buf, ") OVER ");
 
 	foreach(l, context->windowClause)
 	{
@@ -11228,7 +11236,7 @@ generate_function_name(Oid funcid, int nargs, List *argnames, Oid *argtypes,
 								   !use_variadic, true,
 								   &p_funcid, &p_rettype,
 								   &p_retset, &p_nvargs, &p_vatype,
-								   &p_true_typeids, NULL);
+								   &p_true_typeids, NULL, NULL);
 	else
 	{
 		p_result = FUNCDETAIL_NOTFOUND;
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 33dacfd340..5e7be2df29 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -9764,33 +9764,42 @@
   proargtypes => 'int4', prosrc => 'window_ntile' },
 { oid => '3106', descr => 'fetch the preceding row value',
   proname => 'lag', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_lag' },
+  proargtypes => 'anyelement', prosrc => 'window_lag',
+  pronulltreatment => 't' },
 { oid => '3107', descr => 'fetch the Nth preceding row value',
   proname => 'lag', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_lag_with_offset' },
+  proargtypes => 'anyelement int4', prosrc => 'window_lag_with_offset',
+  pronulltreatment => 't' },
 { oid => '3108', descr => 'fetch the Nth preceding row value with default',
   proname => 'lag', prokind => 'w', prorettype => 'anycompatible',
   proargtypes => 'anycompatible int4 anycompatible',
-  prosrc => 'window_lag_with_offset_and_default' },
+  prosrc => 'window_lag_with_offset_and_default',
+  pronulltreatment => 't' },
 { oid => '3109', descr => 'fetch the following row value',
   proname => 'lead', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_lead' },
+  proargtypes => 'anyelement', prosrc => 'window_lead',
+  pronulltreatment => 't' },
 { oid => '3110', descr => 'fetch the Nth following row value',
   proname => 'lead', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_lead_with_offset' },
+  proargtypes => 'anyelement int4', prosrc => 'window_lead_with_offset',
+  pronulltreatment => 't' },
 { oid => '3111', descr => 'fetch the Nth following row value with default',
   proname => 'lead', prokind => 'w', prorettype => 'anycompatible',
   proargtypes => 'anycompatible int4 anycompatible',
-  prosrc => 'window_lead_with_offset_and_default' },
+  prosrc => 'window_lead_with_offset_and_default',
+  pronulltreatment => 't' },
 { oid => '3112', descr => 'fetch the first row value',
   proname => 'first_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_first_value' },
+  proargtypes => 'anyelement', prosrc => 'window_first_value',
+  pronulltreatment => 't' },
 { oid => '3113', descr => 'fetch the last row value',
   proname => 'last_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_last_value' },
+  proargtypes => 'anyelement', prosrc => 'window_last_value',
+  pronulltreatment => 't' },
 { oid => '3114', descr => 'fetch the Nth row value',
   proname => 'nth_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_nth_value' },
+  proargtypes => 'anyelement int4', prosrc => 'window_nth_value',
+  pronulltreatment => 't' },
 
 # functions for range types
 { oid => '3832', descr => 'I/O',
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index f8e6dea22d..31d1dfd465 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -67,6 +67,9 @@ CATALOG(pg_proc,1255,ProcedureRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(81,Proce
 	/* strict with respect to NULLs? */
 	bool		proisstrict BKI_DEFAULT(t);
 
+	/* can handle IGNORE/RESPECT NULLS? (must be window function) */
+	bool		pronulltreatment BKI_DEFAULT(f);
+
 	/* returns a set? */
 	bool		proretset BKI_DEFAULT(f);
 
@@ -198,6 +201,7 @@ extern ObjectAddress ProcedureCreate(const char *procedureName,
 									 bool security_definer,
 									 bool isLeakProof,
 									 bool isStrict,
+									 bool null_treatment,
 									 char volatility,
 									 char parallel,
 									 oidvector *parameterTypes,
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index d1f9ef29ca..06fa070ff2 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -358,6 +358,7 @@ typedef struct FuncCall
 	bool		agg_distinct;	/* arguments were labeled DISTINCT */
 	bool		func_variadic;	/* last argument was labeled VARIADIC */
 	CoercionForm funcformat;	/* how to display this node */
+	NullTreatment	win_null_treatment;	/* IGNORE NULLS or RESPECT NULLS? */
 	int			location;		/* token location, or -1 if unknown */
 } FuncCall;
 
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index 5b190bb99b..9a2a0b4377 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -52,6 +52,13 @@ typedef enum OnCommitAction
 	ONCOMMIT_DROP				/* ON COMMIT DROP */
 } OnCommitAction;
 
+typedef enum NullTreatment
+{
+	NULL_TREATMENT_NONE = 0,
+	NULL_TREATMENT_RESPECT,
+	NULL_TREATMENT_IGNORE
+} NullTreatment;
+
 /*
  * RangeVar - range variable, used in FROM clauses
  *
@@ -379,6 +386,7 @@ typedef struct WindowFunc
 	Index		winref;			/* index of associated WindowClause */
 	bool		winstar;		/* true if argument list was really '*' */
 	bool		winagg;			/* is function a simple aggregate? */
+	NullTreatment	winnulltreatment;	/* can accept RESPECT/IGNORE NULLS? */
 	int			location;		/* token location, or -1 if unknown */
 } WindowFunc;
 
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 71dcdf2889..b288422fda 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -190,6 +190,7 @@ PG_KEYWORD("hold", HOLD, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("hour", HOUR_P, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("identity", IDENTITY_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("if", IF_P, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("ignore", IGNORE_P, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("ilike", ILIKE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("immediate", IMMEDIATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("immutable", IMMUTABLE, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -342,6 +343,7 @@ PG_KEYWORD("repeatable", REPEATABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("replace", REPLACE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("replica", REPLICA, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("reset", RESET, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("respect", RESPECT, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("restart", RESTART, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("restrict", RESTRICT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("returning", RETURNING, RESERVED_KEYWORD, AS_LABEL)
diff --git a/src/include/parser/parse_func.h b/src/include/parser/parse_func.h
index dd189f5452..ead6241525 100644
--- a/src/include/parser/parse_func.h
+++ b/src/include/parser/parse_func.h
@@ -41,7 +41,8 @@ extern FuncDetailCode func_get_detail(List *funcname,
 									  bool expand_variadic, bool expand_defaults,
 									  Oid *funcid, Oid *rettype,
 									  bool *retset, int *nvargs, Oid *vatype,
-									  Oid **true_typeids, List **argdefaults);
+									  Oid **true_typeids, List **argdefaults,
+									  bool *null_treatment);
 
 extern int	func_match_argtypes(int nargs,
 								Oid *input_typeids,
diff --git a/src/test/regress/expected/create_function_3.out b/src/test/regress/expected/create_function_3.out
index ce508ae1dc..0311f8ecc9 100644
--- a/src/test/regress/expected/create_function_3.out
+++ b/src/test/regress/expected/create_function_3.out
@@ -122,6 +122,12 @@ SELECT proname, prosecdef FROM pg_proc
  functest_c_3 | t
 (3 rows)
 
+--
+-- TREAT NULLS
+--
+CREATE FUNCTION functest_D_1(integer) RETURNS integer LANGUAGE 'sql'
+       TREAT NULLS AS 'SELECT $1';
+ERROR:  cannot set null treatment on a non-window function
 --
 -- LEAKPROOF
 --
@@ -298,6 +304,8 @@ CREATE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL AS 'SELECT $1';
 CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL WINDOW AS 'SELECT $1';
 ERROR:  cannot change routine kind
 DETAIL:  "functest1" is a function.
+CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL TREAT NULLS AS 'SELECT $1';
+ERROR:  cannot set null treatment on a non-window function
 CREATE OR REPLACE PROCEDURE functest1(a int) LANGUAGE SQL AS 'SELECT $1';
 ERROR:  cannot change routine kind
 DETAIL:  "functest1" is a function.
diff --git a/src/test/regress/expected/create_procedure.out b/src/test/regress/expected/create_procedure.out
index 3838fa2324..f81f9b79cc 100644
--- a/src/test/regress/expected/create_procedure.out
+++ b/src/test/regress/expected/create_procedure.out
@@ -174,6 +174,10 @@ CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT INTO cp_test VALUES (
 ERROR:  invalid attribute in procedure definition
 LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT I...
                                                ^
+CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
+ERROR:  invalid attribute in procedure definition
+LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INS...
+                                               ^
 CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 ERROR:  invalid attribute in procedure definition
 LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT I...
diff --git a/src/test/regress/expected/misc_sanity.out b/src/test/regress/expected/misc_sanity.out
index d40afeef78..8615d78075 100644
--- a/src/test/regress/expected/misc_sanity.out
+++ b/src/test/regress/expected/misc_sanity.out
@@ -109,3 +109,13 @@ ORDER BY 1, 2;
  pg_largeobject_metadata | lomacl        | aclitem[]
 (11 rows)
 
+-- **************** pg_class ****************
+-- Look for non-window functions with null treatment (there should be none)
+SELECT proname, prokind, pronulltreatment
+FROM pg_proc
+WHERE pronulltreatment AND prokind <> 'w'
+ORDER BY oid;
+ proname | prokind | pronulltreatment 
+---------+---------+------------------
+(0 rows)
+
diff --git a/src/test/regress/expected/window.out b/src/test/regress/expected/window.out
index 19e2ac518a..3bd9584c6c 100644
--- a/src/test/regress/expected/window.out
+++ b/src/test/regress/expected/window.out
@@ -4063,3 +4063,214 @@ SELECT * FROM pg_temp.f(2);
  {5}
 (5 rows)
 
+-- IGNORE NULLS tests
+CREATE TEMPORARY TABLE planets (
+    name text,
+    orbit integer
+);
+INSERT INTO planets VALUES
+  ('mercury', 88),
+  ('venus', 224),
+  ('earth', NULL),
+  ('mars', NULL),
+  ('jupiter', 4332),
+  ('saturn', 24491),
+  ('uranus', NULL),
+  ('neptune', 60182),
+  ('pluto', 90560),
+  ('xyzzy', NULL);
+-- test ruleutils
+CREATE VIEW planets_view AS
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+NOTICE:  view "planets_view" will be a temporary view
+SELECT pg_get_viewdef('planets_view');
+                       pg_get_viewdef                        
+-------------------------------------------------------------
+  SELECT planets.name,                                      +
+     planets.orbit,                                         +
+     lag(planets.orbit) OVER w AS lag,                      +
+     lag(planets.orbit) RESPECT NULLS OVER w AS lag_respect,+
+     lag(planets.orbit) IGNORE NULLS OVER w AS lag_ignore   +
+    FROM planets                                            +
+   WINDOW w AS (ORDER BY planets.name);
+(1 row)
+
+-- lag
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+  name   | orbit |  lag  | lag_respect | lag_ignore 
+---------+-------+-------+-------------+------------
+ earth   |       |       |             |           
+ jupiter |  4332 |       |             |           
+ mars    |       |  4332 |        4332 |       4332
+ mercury |    88 |       |             |       4332
+ neptune | 60182 |    88 |          88 |         88
+ pluto   | 90560 | 60182 |       60182 |      60182
+ saturn  | 24491 | 90560 |       90560 |      90560
+ uranus  |       | 24491 |       24491 |      24491
+ venus   |   224 |       |             |      24491
+ xyzzy   |       |   224 |         224 |        224
+(10 rows)
+
+-- lead
+SELECT name,
+       orbit,
+       lead(orbit) OVER w AS lead,
+       lead(orbit) RESPECT NULLS OVER w AS lead_respect,
+       lead(orbit) IGNORE NULLS OVER w AS lead_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+  name   | orbit | lead  | lead_respect | lead_ignore 
+---------+-------+-------+--------------+-------------
+ earth   |       |  4332 |         4332 |        4332
+ jupiter |  4332 |       |              |          88
+ mars    |       |    88 |           88 |          88
+ mercury |    88 | 60182 |        60182 |       60182
+ neptune | 60182 | 90560 |        90560 |       90560
+ pluto   | 90560 | 24491 |        24491 |       24491
+ saturn  | 24491 |       |              |         224
+ uranus  |       |   224 |          224 |         224
+ venus   |   224 |       |              |            
+ xyzzy   |       |       |              |            
+(10 rows)
+
+-- first_value
+SELECT name,
+       orbit,
+       first_value(orbit) RESPECT NULLS OVER w1,
+       first_value(orbit) IGNORE NULLS OVER w1,
+       first_value(orbit) RESPECT NULLS OVER w2,
+       first_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | first_value | first_value | first_value | first_value 
+---------+-------+-------------+-------------+-------------+-------------
+ earth   |       |             |        4332 |             |        4332
+ jupiter |  4332 |             |        4332 |             |        4332
+ mars    |       |             |        4332 |             |        4332
+ mercury |    88 |             |        4332 |        4332 |        4332
+ neptune | 60182 |             |        4332 |             |          88
+ pluto   | 90560 |             |        4332 |          88 |          88
+ saturn  | 24491 |             |        4332 |       60182 |       60182
+ uranus  |       |             |        4332 |       90560 |       90560
+ venus   |   224 |             |        4332 |       24491 |       24491
+ xyzzy   |       |             |        4332 |             |         224
+(10 rows)
+
+-- nth_value
+SELECT name,
+       orbit,
+       nth_value(orbit, 2) RESPECT NULLS OVER w1,
+       nth_value(orbit, 2) IGNORE NULLS OVER w1,
+       nth_value(orbit, 2) RESPECT NULLS OVER w2,
+       nth_value(orbit, 2) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | nth_value | nth_value | nth_value | nth_value 
+---------+-------+-----------+-----------+-----------+-----------
+ earth   |       |      4332 |        88 |      4332 |          
+ jupiter |  4332 |      4332 |        88 |      4332 |        88
+ mars    |       |      4332 |        88 |      4332 |        88
+ mercury |    88 |      4332 |        88 |           |        88
+ neptune | 60182 |      4332 |        88 |        88 |     60182
+ pluto   | 90560 |      4332 |        88 |     60182 |     60182
+ saturn  | 24491 |      4332 |        88 |     90560 |     90560
+ uranus  |       |      4332 |        88 |     24491 |     24491
+ venus   |   224 |      4332 |        88 |           |       224
+ xyzzy   |       |      4332 |        88 |       224 |          
+(10 rows)
+
+-- last_value
+SELECT name,
+       orbit,
+       last_value(orbit) RESPECT NULLS OVER w1,
+       last_value(orbit) IGNORE NULLS OVER w1,
+       last_value(orbit) RESPECT NULLS OVER w2,
+       last_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | last_value | last_value | last_value | last_value 
+---------+-------+------------+------------+------------+------------
+ earth   |       |            |        224 |            |       4332
+ jupiter |  4332 |            |        224 |         88 |         88
+ mars    |       |            |        224 |      60182 |      60182
+ mercury |    88 |            |        224 |      90560 |      90560
+ neptune | 60182 |            |        224 |      24491 |      24491
+ pluto   | 90560 |            |        224 |            |      24491
+ saturn  | 24491 |            |        224 |        224 |        224
+ uranus  |       |            |        224 |            |        224
+ venus   |   224 |            |        224 |            |        224
+ xyzzy   |       |            |        224 |            |        224
+(10 rows)
+
+-- window function without null treatment
+SELECT row_number() OVER (ORDER BY name) FROM planets;
+ row_number 
+------------
+          1
+          2
+          3
+          4
+          5
+          6
+          7
+          8
+          9
+         10
+(10 rows)
+
+SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM planets; -- fails
+ERROR:  window function row_number does not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM ...
+               ^
+SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM planets; -- fails
+ERROR:  window function row_number does not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM p...
+               ^
+-- regular aggregate
+SELECT sum(orbit) OVER () FROM planets;
+  sum   
+--------
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+(10 rows)
+
+SELECT sum(orbit) RESPECT NULLS OVER () FROM planets; -- fails
+ERROR:  aggregate functions do not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT sum(orbit) RESPECT NULLS OVER () FROM planets;
+               ^
+SELECT sum(orbit) IGNORE NULLS OVER () FROM planets; -- fails
+ERROR:  aggregate functions do not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT sum(orbit) IGNORE NULLS OVER () FROM planets;
+               ^
+--cleanup
+DROP TABLE planets CASCADE;
+NOTICE:  drop cascades to view planets_view
diff --git a/src/test/regress/sql/create_function_3.sql b/src/test/regress/sql/create_function_3.sql
index bd108a918f..f7fe984e58 100644
--- a/src/test/regress/sql/create_function_3.sql
+++ b/src/test/regress/sql/create_function_3.sql
@@ -82,6 +82,12 @@ SELECT proname, prosecdef FROM pg_proc
                      'functest_C_2'::regproc,
                      'functest_C_3'::regproc) ORDER BY proname;
 
+--
+-- TREAT NULLS
+--
+CREATE FUNCTION functest_D_1(integer) RETURNS integer LANGUAGE 'sql'
+       TREAT NULLS AS 'SELECT $1';
+
 --
 -- LEAKPROOF
 --
@@ -190,6 +196,7 @@ DROP FUNCTION functest_b_2;  -- error, ambiguous
 
 CREATE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL AS 'SELECT $1';
 CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL WINDOW AS 'SELECT $1';
+CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL TREAT NULLS AS 'SELECT $1';
 CREATE OR REPLACE PROCEDURE functest1(a int) LANGUAGE SQL AS 'SELECT $1';
 DROP FUNCTION functest1(a int);
 
diff --git a/src/test/regress/sql/create_procedure.sql b/src/test/regress/sql/create_procedure.sql
index 2ef1c82cea..188f5f85a9 100644
--- a/src/test/regress/sql/create_procedure.sql
+++ b/src/test/regress/sql/create_procedure.sql
@@ -130,6 +130,7 @@ CALL version();  -- error: not a procedure
 CALL sum(1);  -- error: not a procedure
 
 CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
+CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 
 ALTER PROCEDURE ptest1(text) STRICT;
diff --git a/src/test/regress/sql/misc_sanity.sql b/src/test/regress/sql/misc_sanity.sql
index 3ce32e4725..ccb4f008d9 100644
--- a/src/test/regress/sql/misc_sanity.sql
+++ b/src/test/regress/sql/misc_sanity.sql
@@ -94,3 +94,12 @@ WHERE c.oid < 16384 AND
       relkind = 'r' AND
       attstorage != 'p'
 ORDER BY 1, 2;
+
+-- **************** pg_class ****************
+
+-- Look for non-window functions with null treatment (there should be none)
+
+SELECT proname, prokind, pronulltreatment
+FROM pg_proc
+WHERE pronulltreatment AND prokind <> 'w'
+ORDER BY oid;
diff --git a/src/test/regress/sql/window.sql b/src/test/regress/sql/window.sql
index eae5fa6017..a021ed3544 100644
--- a/src/test/regress/sql/window.sql
+++ b/src/test/regress/sql/window.sql
@@ -1328,3 +1328,104 @@ $$ LANGUAGE SQL STABLE;
 
 EXPLAIN (costs off) SELECT * FROM pg_temp.f(2);
 SELECT * FROM pg_temp.f(2);
+
+
+-- IGNORE NULLS tests
+
+CREATE TEMPORARY TABLE planets (
+    name text,
+    orbit integer
+);
+
+INSERT INTO planets VALUES
+  ('mercury', 88),
+  ('venus', 224),
+  ('earth', NULL),
+  ('mars', NULL),
+  ('jupiter', 4332),
+  ('saturn', 24491),
+  ('uranus', NULL),
+  ('neptune', 60182),
+  ('pluto', 90560),
+  ('xyzzy', NULL);
+
+-- test ruleutils
+CREATE VIEW planets_view AS
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+SELECT pg_get_viewdef('planets_view');
+
+-- lag
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+
+-- lead
+SELECT name,
+       orbit,
+       lead(orbit) OVER w AS lead,
+       lead(orbit) RESPECT NULLS OVER w AS lead_respect,
+       lead(orbit) IGNORE NULLS OVER w AS lead_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+
+-- first_value
+SELECT name,
+       orbit,
+       first_value(orbit) RESPECT NULLS OVER w1,
+       first_value(orbit) IGNORE NULLS OVER w1,
+       first_value(orbit) RESPECT NULLS OVER w2,
+       first_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- nth_value
+SELECT name,
+       orbit,
+       nth_value(orbit, 2) RESPECT NULLS OVER w1,
+       nth_value(orbit, 2) IGNORE NULLS OVER w1,
+       nth_value(orbit, 2) RESPECT NULLS OVER w2,
+       nth_value(orbit, 2) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- last_value
+SELECT name,
+       orbit,
+       last_value(orbit) RESPECT NULLS OVER w1,
+       last_value(orbit) IGNORE NULLS OVER w1,
+       last_value(orbit) RESPECT NULLS OVER w2,
+       last_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- window function without null treatment
+SELECT row_number() OVER (ORDER BY name) FROM planets;
+SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM planets; -- fails
+SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM planets; -- fails
+
+-- regular aggregate
+SELECT sum(orbit) OVER () FROM planets;
+SELECT sum(orbit) RESPECT NULLS OVER () FROM planets; -- fails
+SELECT sum(orbit) IGNORE NULLS OVER () FROM planets; -- fails
+
+--cleanup
+DROP TABLE planets CASCADE;

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 5021ac1ca9..0e877c48df 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -20373,6 +20373,14 @@ SELECT count(*) FROM sometable;
    about frame specifications.
   </para>
 
+  <para>
+   The functions <function>lead</function>, <function>lag</function>,
+   <function>first_value</function>, <function>last_value</function>, and
+   <function>nth_value</function> accept a null treatment option which is
+   <literal>RESPECT NULLS</literal> or <literal>IGNORE NULLS</literal>.
+   If this option is not specified, the default is <literal>RESPECT NULLS</literal>.
+  </para>
+
   <para>
    When an aggregate function is used as a window function, it aggregates
    over the rows within the current row's window frame.
@@ -20386,14 +20394,9 @@ SELECT count(*) FROM sometable;
 
   <note>
    <para>
-    The SQL standard defines a <literal>RESPECT NULLS</literal> or
-    <literal>IGNORE NULLS</literal> option for <function>lead</function>, <function>lag</function>,
-    <function>first_value</function>, <function>last_value</function>, and
-    <function>nth_value</function>.  This is not implemented in
-    <productname>PostgreSQL</productname>: the behavior is always the
-    same as the standard's default, namely <literal>RESPECT NULLS</literal>.
-    Likewise, the standard's <literal>FROM FIRST</literal> or <literal>FROM LAST</literal>
-    option for <function>nth_value</function> is not implemented: only the
+    The SQL standard defines a <literal>FROM FIRST</literal> or <literal>FROM LAST</literal>
+    option for <function>nth_value</function>.  This is not implemented in
+    <productname>PostgreSQL</productname>: only the
     default <literal>FROM FIRST</literal> behavior is supported.  (You can achieve
     the result of <literal>FROM LAST</literal> by reversing the <literal>ORDER BY</literal>
     ordering.)
diff --git a/doc/src/sgml/ref/create_function.sgml b/doc/src/sgml/ref/create_function.sgml
index 3c1eaea651..31e08c26b4 100644
--- a/doc/src/sgml/ref/create_function.sgml
+++ b/doc/src/sgml/ref/create_function.sgml
@@ -28,6 +28,7 @@ CREATE [ OR REPLACE ] FUNCTION
   { LANGUAGE <replaceable class="parameter">lang_name</replaceable>
     | TRANSFORM { FOR TYPE <replaceable class="parameter">type_name</replaceable> } [, ... ]
     | WINDOW
+    | TREAT NULLS
     | IMMUTABLE | STABLE | VOLATILE | [ NOT ] LEAKPROOF
     | CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
     | [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
@@ -293,6 +294,17 @@ CREATE [ OR REPLACE ] FUNCTION
      </listitem>
     </varlistentry>
 
+    <varlistentry>
+     <term><literal>TREAT NULLS</literal></term>
+
+     <listitem>
+      <para><literal>TREAT NULLS</literal> indicates that the function is able
+      to handle the <literal>RESPECT NULLS</literal> and <literal>IGNORE
+      NULLS</literal> options.  Only window functions may specify this.
+      </para>
+     </listitem>
+    </varlistentry>
+
     <varlistentry>
      <term><literal>IMMUTABLE</literal></term>
      <term><literal>STABLE</literal></term>
diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml
index d66560b587..103595d21b 100644
--- a/doc/src/sgml/syntax.sgml
+++ b/doc/src/sgml/syntax.sgml
@@ -1766,6 +1766,8 @@ FROM generate_series(1,10) AS s(i);
     The syntax of a window function call is one of the following:
 
 <synopsis>
+<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ RESPECT NULLS | IGNORE NULLS ] OVER <replaceable>window_name</replaceable>
+<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ RESPECT NULLS | IGNORE NULLS ] OVER ( <replaceable class="parameter">window_definition</replaceable> )
 <replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER <replaceable>window_name</replaceable>
 <replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER ( <replaceable class="parameter">window_definition</replaceable> )
 <replaceable>function_name</replaceable> ( * ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER <replaceable>window_name</replaceable>
@@ -1779,6 +1781,18 @@ FROM generate_series(1,10) AS s(i);
 [ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [ NULLS { FIRST | LAST } ] [, ...] ]
 [ <replaceable class="parameter">frame_clause</replaceable> ]
 </synopsis>
+   </para>
+
+   <note>
+    <para>
+     The versions with <literal>RESPECT NULLS</literal> or <literal>IGNORE
+     NULLS</literal> only apply to true window functions, whereas the versions
+     with <literal>FILTER</literal> only apply to aggregate functions used as
+     window functions.
+    </para>
+   </note>
+
+   <para>
     The optional <replaceable class="parameter">frame_clause</replaceable>
     can be one of
 <synopsis>
diff --git a/src/backend/catalog/pg_aggregate.c b/src/backend/catalog/pg_aggregate.c
index 7664bb6285..fea8778ec8 100644
--- a/src/backend/catalog/pg_aggregate.c
+++ b/src/backend/catalog/pg_aggregate.c
@@ -627,6 +627,7 @@ AggregateCreate(const char *aggName,
 									 * definable for agg) */
 							 false, /* isLeakProof */
 							 false, /* isStrict (not needed for agg) */
+							 false, /* null_treatment (not needed for agg) */
 							 PROVOLATILE_IMMUTABLE, /* volatility (not needed
 													 * for agg) */
 							 proparallel,
@@ -848,7 +849,7 @@ lookup_agg_function(List *fnName,
 							   nargs, input_types, false, false,
 							   &fnOid, rettype, &retset,
 							   &nvargs, &vatype,
-							   &true_oid_array, NULL);
+							   &true_oid_array, NULL, NULL);
 
 	/* only valid case is a normal function not returning a set */
 	if (fdresult != FUNCDETAIL_NORMAL || !OidIsValid(fnOid))
diff --git a/src/backend/catalog/pg_proc.c b/src/backend/catalog/pg_proc.c
index 1dd9ecc063..2783b0d630 100644
--- a/src/backend/catalog/pg_proc.c
+++ b/src/backend/catalog/pg_proc.c
@@ -80,6 +80,7 @@ ProcedureCreate(const char *procedureName,
 				bool security_definer,
 				bool isLeakProof,
 				bool isStrict,
+				bool null_treatment,
 				char volatility,
 				char parallel,
 				oidvector *parameterTypes,
@@ -307,6 +308,7 @@ ProcedureCreate(const char *procedureName,
 	values[Anum_pg_proc_prosecdef - 1] = BoolGetDatum(security_definer);
 	values[Anum_pg_proc_proleakproof - 1] = BoolGetDatum(isLeakProof);
 	values[Anum_pg_proc_proisstrict - 1] = BoolGetDatum(isStrict);
+	values[Anum_pg_proc_pronulltreatment - 1] = BoolGetDatum(null_treatment);
 	values[Anum_pg_proc_proretset - 1] = BoolGetDatum(returnsSet);
 	values[Anum_pg_proc_provolatile - 1] = CharGetDatum(volatility);
 	values[Anum_pg_proc_proparallel - 1] = CharGetDatum(parallel);
@@ -386,6 +388,12 @@ ProcedureCreate(const char *procedureName,
 					  errdetail("\"%s\" is a window function.", procedureName) :
 					  0)));
 
+		/* Not okay to set null treatment if not a window function */
+		if (null_treatment && oldproc->prokind != PROKIND_WINDOW)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+					 errmsg("cannot set null treatment on a non-window function")));
+
 		dropcmd = (prokind == PROKIND_PROCEDURE ? "DROP PROCEDURE" :
 				   prokind == PROKIND_AGGREGATE ? "DROP AGGREGATE" :
 				   "DROP FUNCTION");
diff --git a/src/backend/commands/functioncmds.c b/src/backend/commands/functioncmds.c
index c3ce480c8f..245a768463 100644
--- a/src/backend/commands/functioncmds.c
+++ b/src/backend/commands/functioncmds.c
@@ -697,6 +697,7 @@ compute_function_attributes(ParseState *pstate,
 							bool *windowfunc_p,
 							char *volatility_p,
 							bool *strict_p,
+							bool *null_treatment_p,
 							bool *security_definer,
 							bool *leakproof_p,
 							ArrayType **proconfig,
@@ -710,6 +711,7 @@ compute_function_attributes(ParseState *pstate,
 	DefElem    *language_item = NULL;
 	DefElem    *transform_item = NULL;
 	DefElem    *windowfunc_item = NULL;
+	DefElem    *nulltreatment_item = NULL;
 	DefElem    *volatility_item = NULL;
 	DefElem    *strict_item = NULL;
 	DefElem    *security_item = NULL;
@@ -765,6 +767,20 @@ compute_function_attributes(ParseState *pstate,
 						 parser_errposition(pstate, defel->location)));
 			windowfunc_item = defel;
 		}
+		else if (strcmp(defel->defname, "null_treatment") == 0)
+		{
+			if (nulltreatment_item)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 parser_errposition(pstate, defel->location)));
+			if (is_procedure)
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+						 errmsg("invalid attribute in procedure definition"),
+						 parser_errposition(pstate, defel->location)));
+			nulltreatment_item = defel;
+		}
 		else if (compute_common_attribute(pstate,
 										  is_procedure,
 										  defel,
@@ -816,6 +832,14 @@ compute_function_attributes(ParseState *pstate,
 		*volatility_p = interpret_func_volatility(volatility_item);
 	if (strict_item)
 		*strict_p = intVal(strict_item->arg);
+	if (nulltreatment_item)
+	{
+		*null_treatment_p = intVal(nulltreatment_item->arg);
+		if (*null_treatment_p && !*windowfunc_p)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+					 errmsg("cannot set null treatment on a non-window function")));
+	}
 	if (security_item)
 		*security_definer = intVal(security_item->arg);
 	if (leakproof_item)
@@ -941,6 +965,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 				isStrict,
 				security,
 				isLeakProof;
+	bool		null_treatment;
 	char		volatility;
 	ArrayType  *proconfig;
 	float4		procost;
@@ -964,6 +989,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 	/* Set default attributes */
 	isWindowFunc = false;
 	isStrict = false;
+	null_treatment = false;
 	security = false;
 	isLeakProof = false;
 	volatility = PROVOLATILE_VOLATILE;
@@ -979,7 +1005,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 								stmt->options,
 								&as_clause, &language, &transformDefElem,
 								&isWindowFunc, &volatility,
-								&isStrict, &security, &isLeakProof,
+								&isStrict, &null_treatment, &security, &isLeakProof,
 								&proconfig, &procost, &prorows,
 								&prosupport, &parallel);
 
@@ -1159,6 +1185,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 						   security,
 						   isLeakProof,
 						   isStrict,
+						   null_treatment,
 						   volatility,
 						   parallel,
 						   parameterTypes,
diff --git a/src/backend/commands/typecmds.c b/src/backend/commands/typecmds.c
index a0a8695b1b..6331c790c9 100644
--- a/src/backend/commands/typecmds.c
+++ b/src/backend/commands/typecmds.c
@@ -1779,6 +1779,7 @@ makeRangeConstructors(const char *name, Oid namespace,
 								 false, /* security_definer */
 								 false, /* leakproof */
 								 false, /* isStrict */
+								 false, /* null_treatment */
 								 PROVOLATILE_IMMUTABLE, /* volatility */
 								 PROPARALLEL_SAFE,	/* parallel safety */
 								 constructorArgTypesVector, /* parameterTypes */
diff --git a/src/backend/executor/nodeWindowAgg.c b/src/backend/executor/nodeWindowAgg.c
index de58df3d3f..832b40b849 100644
--- a/src/backend/executor/nodeWindowAgg.c
+++ b/src/backend/executor/nodeWindowAgg.c
@@ -68,6 +68,7 @@ typedef struct WindowObjectData
 	int			readptr;		/* tuplestore read pointer for this fn */
 	int64		markpos;		/* row that markptr is positioned on */
 	int64		seekpos;		/* row that readptr is positioned on */
+	NullTreatment	null_treatment;	/* RESPECT/IGNORE NULLS? */
 } WindowObjectData;
 
 /*
@@ -2473,6 +2474,7 @@ ExecInitWindowAgg(WindowAgg *node, EState *estate, int eflags)
 			winobj->winstate = winstate;
 			winobj->argstates = wfuncstate->args;
 			winobj->localmem = NULL;
+			winobj->null_treatment = wfunc->winnulltreatment;
 			perfuncstate->winobj = winobj;
 
 			/* It's a real window function, so set up to call it. */
@@ -3173,48 +3175,103 @@ WinGetFuncArgInPartition(WindowObject winobj, int argno,
 	TupleTableSlot *slot;
 	bool		gottuple;
 	int64		abs_pos;
+	bool		ignore_nulls = false;
+	int			target = relpos;
+	int			step;
+	Datum		result;
 
 	Assert(WindowObjectIsValid(winobj));
 	winstate = winobj->winstate;
 	econtext = winstate->ss.ps.ps_ExprContext;
 	slot = winstate->temp_slot_1;
 
-	switch (seektype)
+	/*
+	 * If we're not ignoring nulls, we'll just go straight to the desired row.
+	 * But if we are ignoring nulls, we'll have to step towards the target row
+	 * by row so we need to determine how we get there.
+	 */
+	if (winobj->null_treatment == NULL_TREATMENT_IGNORE)
 	{
-		case WINDOW_SEEK_CURRENT:
-			abs_pos = winstate->currentpos + relpos;
-			break;
-		case WINDOW_SEEK_HEAD:
-			abs_pos = relpos;
-			break;
-		case WINDOW_SEEK_TAIL:
-			spool_tuples(winstate, -1);
-			abs_pos = winstate->spooled_rows - 1 + relpos;
-			break;
-		default:
-			elog(ERROR, "unrecognized window seek type: %d", seektype);
-			abs_pos = 0;		/* keep compiler quiet */
-			break;
-	}
-
-	gottuple = window_gettupleslot(winobj, abs_pos, slot);
+		ignore_nulls = true;
 
-	if (!gottuple)
-	{
-		if (isout)
-			*isout = true;
-		*isnull = true;
-		return (Datum) 0;
+		if (seektype == WINDOW_SEEK_HEAD)
+		{
+			step = 1;
+			relpos = 0;
+		}
+		else if (seektype == WINDOW_SEEK_TAIL)
+		{
+			step = -1;
+			relpos = 0;
+		}
+		else
+		{
+			if (target > 0)
+				step = 1;
+			else if (target < 0)
+				step = -1;
+			else
+				step = 0;
+			relpos = step;
+		}
 	}
-	else
+
+	for (;;)
 	{
-		if (isout)
-			*isout = false;
-		if (set_mark)
-			WinSetMarkPosition(winobj, abs_pos);
+		switch (seektype)
+		{
+			case WINDOW_SEEK_CURRENT:
+				abs_pos = winstate->currentpos + relpos;
+				break;
+			case WINDOW_SEEK_HEAD:
+				abs_pos = relpos;
+				break;
+			case WINDOW_SEEK_TAIL:
+				spool_tuples(winstate, -1);
+				abs_pos = winstate->spooled_rows - 1 + relpos;
+				break;
+			default:
+				elog(ERROR, "unrecognized window seek type: %d", seektype);
+				abs_pos = 0;		/* keep compiler quiet */
+				break;
+		}
+
+		gottuple = window_gettupleslot(winobj, abs_pos, slot);
+
+		/* Did we fall off the end of the partition? */
+		if (!gottuple)
+		{
+			if (isout)
+				*isout = true;
+			*isnull = true;
+			return (Datum) 0;
+		}
+
+		/* Evaluate the expression at this row */
 		econtext->ecxt_outertuple = slot;
-		return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
-							econtext, isnull);
+		result = ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
+							  econtext, isnull);
+
+		/* If we got a null and we're ignoring them, move the goalposts */
+		if (ignore_nulls && *isnull)
+			target += step;
+
+		/* Once we've reached our target, we're done */
+		if (relpos == target)
+		{
+			if (isout)
+				*isout = false;
+			/*
+			 * We can only mark the row if we're not ignoring nulls (because we
+			 * jump straight there).
+			 */
+			if (set_mark && !ignore_nulls)
+				WinSetMarkPosition(winobj, abs_pos);
+			return result;
+		}
+
+		/* Otherwise move closer and try again */
+		relpos += step;
 	}
 }
 
@@ -3261,170 +3318,218 @@ WinGetFuncArgInFrame(WindowObject winobj, int argno,
 	TupleTableSlot *slot;
 	int64		abs_pos;
 	int64		mark_pos;
+	bool		ignore_nulls = false;
+	int			target = relpos;
+	int			step;
+	Datum		result;
 
 	Assert(WindowObjectIsValid(winobj));
 	winstate = winobj->winstate;
 	econtext = winstate->ss.ps.ps_ExprContext;
 	slot = winstate->temp_slot_1;
 
-	switch (seektype)
+	/*
+	 * If we're not ignoring nulls, we'll just go straight to the desired row.
+	 * But if we are ignoring nulls, we'll have to step towards the target row
+	 * by row so we need to determine how we get there.
+	 */
+	if (winobj->null_treatment == NULL_TREATMENT_IGNORE)
 	{
-		case WINDOW_SEEK_CURRENT:
-			elog(ERROR, "WINDOW_SEEK_CURRENT is not supported for WinGetFuncArgInFrame");
-			abs_pos = mark_pos = 0; /* keep compiler quiet */
-			break;
-		case WINDOW_SEEK_HEAD:
-			/* rejecting relpos < 0 is easy and simplifies code below */
-			if (relpos < 0)
-				goto out_of_frame;
-			update_frameheadpos(winstate);
-			abs_pos = winstate->frameheadpos + relpos;
-			mark_pos = abs_pos;
+		ignore_nulls = true;
 
-			/*
-			 * Account for exclusion option if one is active, but advance only
-			 * abs_pos not mark_pos.  This prevents changes of the current
-			 * row's peer group from resulting in trying to fetch a row before
-			 * some previous mark position.
-			 *
-			 * Note that in some corner cases such as current row being
-			 * outside frame, these calculations are theoretically too simple,
-			 * but it doesn't matter because we'll end up deciding the row is
-			 * out of frame.  We do not attempt to avoid fetching rows past
-			 * end of frame; that would happen in some cases anyway.
-			 */
-			switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
-			{
-				case 0:
-					/* no adjustment needed */
-					break;
-				case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
-					if (abs_pos >= winstate->currentpos &&
-						winstate->currentpos >= winstate->frameheadpos)
-						abs_pos++;
-					break;
-				case FRAMEOPTION_EXCLUDE_GROUP:
-					update_grouptailpos(winstate);
-					if (abs_pos >= winstate->groupheadpos &&
-						winstate->grouptailpos > winstate->frameheadpos)
-					{
-						int64		overlapstart = Max(winstate->groupheadpos,
-													   winstate->frameheadpos);
+		if (target > 0)
+			step = 1;
+		else if (target < 0)
+			step = -1;
+		else if (seektype == WINDOW_SEEK_HEAD)
+			step = 1;
+		else if (seektype == WINDOW_SEEK_TAIL)
+			step = -1;
+		else
+			step = 0;
 
-						abs_pos += winstate->grouptailpos - overlapstart;
-					}
-					break;
-				case FRAMEOPTION_EXCLUDE_TIES:
-					update_grouptailpos(winstate);
-					if (abs_pos >= winstate->groupheadpos &&
-						winstate->grouptailpos > winstate->frameheadpos)
-					{
-						int64		overlapstart = Max(winstate->groupheadpos,
-													   winstate->frameheadpos);
+		relpos = 0;
+	}
 
-						if (abs_pos == overlapstart)
-							abs_pos = winstate->currentpos;
-						else
-							abs_pos += winstate->grouptailpos - overlapstart - 1;
-					}
-					break;
-				default:
-					elog(ERROR, "unrecognized frame option state: 0x%x",
-						 winstate->frameOptions);
-					break;
-			}
-			break;
-		case WINDOW_SEEK_TAIL:
-			/* rejecting relpos > 0 is easy and simplifies code below */
-			if (relpos > 0)
-				goto out_of_frame;
-			update_frametailpos(winstate);
-			abs_pos = winstate->frametailpos - 1 + relpos;
+	for (;;)
+	{
+		switch (seektype)
+		{
+			case WINDOW_SEEK_CURRENT:
+				elog(ERROR, "WINDOW_SEEK_CURRENT is not supported for WinGetFuncArgInFrame");
+				abs_pos = mark_pos = 0; /* keep compiler quiet */
+				break;
+			case WINDOW_SEEK_HEAD:
+				/* rejecting relpos < 0 is easy and simplifies code below */
+				if (relpos < 0)
+					goto out_of_frame;
+				update_frameheadpos(winstate);
+				abs_pos = winstate->frameheadpos + relpos;
+				mark_pos = abs_pos;
 
-			/*
-			 * Account for exclusion option if one is active.  If there is no
-			 * exclusion, we can safely set the mark at the accessed row.  But
-			 * if there is, we can only mark the frame start, because we can't
-			 * be sure how far back in the frame the exclusion might cause us
-			 * to fetch in future.  Furthermore, we have to actually check
-			 * against frameheadpos here, since it's unsafe to try to fetch a
-			 * row before frame start if the mark might be there already.
-			 */
-			switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
-			{
-				case 0:
-					/* no adjustment needed */
-					mark_pos = abs_pos;
-					break;
-				case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
-					if (abs_pos <= winstate->currentpos &&
-						winstate->currentpos < winstate->frametailpos)
-						abs_pos--;
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				case FRAMEOPTION_EXCLUDE_GROUP:
-					update_grouptailpos(winstate);
-					if (abs_pos < winstate->grouptailpos &&
-						winstate->groupheadpos < winstate->frametailpos)
-					{
-						int64		overlapend = Min(winstate->grouptailpos,
-													 winstate->frametailpos);
+				/*
+				 * Account for exclusion option if one is active, but advance only
+				 * abs_pos not mark_pos.  This prevents changes of the current
+				 * row's peer group from resulting in trying to fetch a row before
+				 * some previous mark position.
+				 *
+				 * Note that in some corner cases such as current row being
+				 * outside frame, these calculations are theoretically too simple,
+				 * but it doesn't matter because we'll end up deciding the row is
+				 * out of frame.  We do not attempt to avoid fetching rows past
+				 * end of frame; that would happen in some cases anyway.
+				 */
+				switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
+				{
+					case 0:
+						/* no adjustment needed */
+						break;
+					case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
+						if (abs_pos >= winstate->currentpos &&
+							winstate->currentpos >= winstate->frameheadpos)
+							abs_pos++;
+						break;
+					case FRAMEOPTION_EXCLUDE_GROUP:
+						update_grouptailpos(winstate);
+						if (abs_pos >= winstate->groupheadpos &&
+							winstate->grouptailpos > winstate->frameheadpos)
+						{
+							int64		overlapstart = Max(winstate->groupheadpos,
+														   winstate->frameheadpos);
+
+							abs_pos += winstate->grouptailpos - overlapstart;
+						}
+						break;
+					case FRAMEOPTION_EXCLUDE_TIES:
+						update_grouptailpos(winstate);
+						if (abs_pos >= winstate->groupheadpos &&
+							winstate->grouptailpos > winstate->frameheadpos)
+						{
+							int64		overlapstart = Max(winstate->groupheadpos,
+														   winstate->frameheadpos);
+
+							if (abs_pos == overlapstart)
+								abs_pos = winstate->currentpos;
+							else
+								abs_pos += winstate->grouptailpos - overlapstart - 1;
+						}
+						break;
+					default:
+						elog(ERROR, "unrecognized frame option state: 0x%x",
+							 winstate->frameOptions);
+						break;
+				}
+				break;
+			case WINDOW_SEEK_TAIL:
+				/* rejecting relpos > 0 is easy and simplifies code below */
+				if (relpos > 0)
+					goto out_of_frame;
+				update_frametailpos(winstate);
+				abs_pos = winstate->frametailpos - 1 + relpos;
 
-						abs_pos -= overlapend - winstate->groupheadpos;
-					}
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				case FRAMEOPTION_EXCLUDE_TIES:
-					update_grouptailpos(winstate);
-					if (abs_pos < winstate->grouptailpos &&
-						winstate->groupheadpos < winstate->frametailpos)
-					{
-						int64		overlapend = Min(winstate->grouptailpos,
-													 winstate->frametailpos);
+				/*
+				 * Account for exclusion option if one is active.  If there is no
+				 * exclusion, we can safely set the mark at the accessed row.  But
+				 * if there is, we can only mark the frame start, because we can't
+				 * be sure how far back in the frame the exclusion might cause us
+				 * to fetch in future.  Furthermore, we have to actually check
+				 * against frameheadpos here, since it's unsafe to try to fetch a
+				 * row before frame start if the mark might be there already.
+				 */
+				switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
+				{
+					case 0:
+						/* no adjustment needed */
+						mark_pos = abs_pos;
+						break;
+					case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
+						if (abs_pos <= winstate->currentpos &&
+							winstate->currentpos < winstate->frametailpos)
+							abs_pos--;
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					case FRAMEOPTION_EXCLUDE_GROUP:
+						update_grouptailpos(winstate);
+						if (abs_pos < winstate->grouptailpos &&
+							winstate->groupheadpos < winstate->frametailpos)
+						{
+							int64		overlapend = Min(winstate->grouptailpos,
+														 winstate->frametailpos);
+
+							abs_pos -= overlapend - winstate->groupheadpos;
+						}
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					case FRAMEOPTION_EXCLUDE_TIES:
+						update_grouptailpos(winstate);
+						if (abs_pos < winstate->grouptailpos &&
+							winstate->groupheadpos < winstate->frametailpos)
+						{
+							int64		overlapend = Min(winstate->grouptailpos,
+														 winstate->frametailpos);
+
+							if (abs_pos == overlapend - 1)
+								abs_pos = winstate->currentpos;
+							else
+								abs_pos -= overlapend - 1 - winstate->groupheadpos;
+						}
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					default:
+						elog(ERROR, "unrecognized frame option state: 0x%x",
+							 winstate->frameOptions);
+						mark_pos = 0;	/* keep compiler quiet */
+						break;
+				}
+				break;
+			default:
+				elog(ERROR, "unrecognized window seek type: %d", seektype);
+				abs_pos = mark_pos = 0; /* keep compiler quiet */
+				break;
+		}
 
-						if (abs_pos == overlapend - 1)
-							abs_pos = winstate->currentpos;
-						else
-							abs_pos -= overlapend - 1 - winstate->groupheadpos;
-					}
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				default:
-					elog(ERROR, "unrecognized frame option state: 0x%x",
-						 winstate->frameOptions);
-					mark_pos = 0;	/* keep compiler quiet */
-					break;
-			}
-			break;
-		default:
-			elog(ERROR, "unrecognized window seek type: %d", seektype);
-			abs_pos = mark_pos = 0; /* keep compiler quiet */
-			break;
-	}
+		if (!window_gettupleslot(winobj, abs_pos, slot))
+			goto out_of_frame;
 
-	if (!window_gettupleslot(winobj, abs_pos, slot))
-		goto out_of_frame;
+		/* The code above does not detect all out-of-frame cases, so check */
+		if (row_is_in_frame(winstate, abs_pos, slot) <= 0)
+			goto out_of_frame;
 
-	/* The code above does not detect all out-of-frame cases, so check */
-	if (row_is_in_frame(winstate, abs_pos, slot) <= 0)
-		goto out_of_frame;
+		/* Evaluate the expression at this row */
+		econtext->ecxt_outertuple = slot;
+		result = ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
+							  econtext, isnull);
 
-	if (isout)
-		*isout = false;
-	if (set_mark)
-		WinSetMarkPosition(winobj, mark_pos);
-	econtext->ecxt_outertuple = slot;
-	return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
-						econtext, isnull);
+		/* If we got a null and we're ignoring them, move the goalposts */
+		if (ignore_nulls && *isnull)
+			target += step;
+
+		/* Once we've reached our target, we're done */
+		if (relpos == target)
+		{
+			if (isout)
+				*isout = false;
+			/*
+			 * We can only mark the row if we're not ignoring nulls (because we
+			 * jump straight there).
+			 */
+			if (set_mark && !ignore_nulls)
+				WinSetMarkPosition(winobj, mark_pos);
+			return result;
+		}
+
+		/* Otherwise move closer and try again */
+		relpos += step;
+	}
 
 out_of_frame:
 	if (isout)
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 70f8b718e0..eba1f3f4d2 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -1533,6 +1533,7 @@ _copyWindowFunc(const WindowFunc *from)
 	COPY_SCALAR_FIELD(winref);
 	COPY_SCALAR_FIELD(winstar);
 	COPY_SCALAR_FIELD(winagg);
+	COPY_SCALAR_FIELD(winnulltreatment);
 	COPY_LOCATION_FIELD(location);
 
 	return newnode;
@@ -2691,6 +2692,7 @@ _copyFuncCall(const FuncCall *from)
 	COPY_SCALAR_FIELD(agg_distinct);
 	COPY_SCALAR_FIELD(func_variadic);
 	COPY_SCALAR_FIELD(funcformat);
+	COPY_SCALAR_FIELD(win_null_treatment);
 	COPY_LOCATION_FIELD(location);
 
 	return newnode;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 541e0e6b48..effed2f811 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -266,6 +266,7 @@ _equalWindowFunc(const WindowFunc *a, const WindowFunc *b)
 	COMPARE_SCALAR_FIELD(winref);
 	COMPARE_SCALAR_FIELD(winstar);
 	COMPARE_SCALAR_FIELD(winagg);
+	COMPARE_SCALAR_FIELD(winnulltreatment);
 	COMPARE_LOCATION_FIELD(location);
 
 	return true;
@@ -2380,6 +2381,7 @@ _equalFuncCall(const FuncCall *a, const FuncCall *b)
 	COMPARE_SCALAR_FIELD(agg_distinct);
 	COMPARE_SCALAR_FIELD(func_variadic);
 	COMPARE_SCALAR_FIELD(funcformat);
+	COMPARE_SCALAR_FIELD(win_null_treatment);
 	COMPARE_LOCATION_FIELD(location);
 
 	return true;
diff --git a/src/backend/nodes/makefuncs.c b/src/backend/nodes/makefuncs.c
index ee033ae779..587cd43e6b 100644
--- a/src/backend/nodes/makefuncs.c
+++ b/src/backend/nodes/makefuncs.c
@@ -596,6 +596,7 @@ makeFuncCall(List *name, List *args, CoercionForm funcformat, int location)
 	n->agg_distinct = false;
 	n->func_variadic = false;
 	n->funcformat = funcformat;
+	n->win_null_treatment = NULL_TREATMENT_NONE;
 	n->location = location;
 	return n;
 }
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index d78b16ed1d..164751a357 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -1184,6 +1184,7 @@ _outWindowFunc(StringInfo str, const WindowFunc *node)
 	WRITE_UINT_FIELD(winref);
 	WRITE_BOOL_FIELD(winstar);
 	WRITE_BOOL_FIELD(winagg);
+	WRITE_INT_FIELD(winnulltreatment);
 	WRITE_LOCATION_FIELD(location);
 }
 
@@ -2790,6 +2791,7 @@ _outFuncCall(StringInfo str, const FuncCall *node)
 	WRITE_BOOL_FIELD(agg_distinct);
 	WRITE_BOOL_FIELD(func_variadic);
 	WRITE_ENUM_FIELD(funcformat, CoercionForm);
+	WRITE_BOOL_FIELD(win_null_treatment);
 	WRITE_LOCATION_FIELD(location);
 }
 
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index 0f6a77afc4..587757f2c9 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -656,6 +656,7 @@ _readWindowFunc(void)
 	READ_UINT_FIELD(winref);
 	READ_BOOL_FIELD(winstar);
 	READ_BOOL_FIELD(winagg);
+	READ_INT_FIELD(winnulltreatment);
 	READ_LOCATION_FIELD(location);
 
 	READ_DONE();
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 8f5cbf99f4..85ea709d81 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -2221,6 +2221,7 @@ eval_const_expressions_mutator(Node *node,
 				newexpr->winref = expr->winref;
 				newexpr->winstar = expr->winstar;
 				newexpr->winagg = expr->winagg;
+				newexpr->winnulltreatment = expr->winnulltreatment;
 				newexpr->location = expr->location;
 
 				return (Node *) newexpr;
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 8f341ac006..59d72207c9 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -582,6 +582,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <list>	window_clause window_definition_list opt_partition_clause
 %type <windef>	window_definition over_clause window_specification
 				opt_frame_clause frame_extent frame_bound
+%type <ival>	null_treatment
 %type <ival>	opt_window_exclusion_clause
 %type <str>		opt_existing_window_name
 %type <boolean> opt_if_not_exists
@@ -650,7 +651,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 	HANDLER HAVING HEADER_P HOLD HOUR_P
 
-	IDENTITY_P IF_P ILIKE IMMEDIATE IMMUTABLE IMPLICIT_P IMPORT_P IN_P INCLUDE
+	IDENTITY_P IF_P IGNORE_P ILIKE IMMEDIATE IMMUTABLE IMPLICIT_P IMPORT_P IN_P INCLUDE
 	INCLUDING INCREMENT INDEX INDEXES INHERIT INHERITS INITIALLY INLINE_P
 	INNER_P INOUT INPUT_P INSENSITIVE INSERT INSTEAD INT_P INTEGER
 	INTERSECT INTERVAL INTO INVOKER IS ISNULL ISOLATION
@@ -682,7 +683,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 	RANGE READ REAL REASSIGN RECHECK RECURSIVE REF REFERENCES REFERENCING
 	REFRESH REINDEX RELATIVE_P RELEASE RENAME REPEATABLE REPLACE REPLICA
-	RESET RESTART RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROLLUP
+	RESET RESPECT RESTART RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROLLUP
 	ROUTINE ROUTINES ROW ROWS RULE
 
 	SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
@@ -7799,6 +7800,10 @@ createfunc_opt_item:
 				{
 					$$ = makeDefElem("window", (Node *)makeInteger(true), @1);
 				}
+			| TREAT NULLS_P
+				{
+					$$ = makeDefElem("null_treatment", (Node *)makeInteger(true), @1);
+				}
 			| common_func_opt_item
 				{
 					$$ = $1;
@@ -13676,6 +13681,14 @@ func_expr: func_application within_group_clause filter_clause over_clause
 					}
 					n->agg_filter = $3;
 					n->over = $4;
+					n->win_null_treatment = NULL_TREATMENT_NONE;
+					$$ = (Node *) n;
+				}
+			| func_application null_treatment over_clause
+				{
+					FuncCall *n = (FuncCall *) $1;
+					n->over = $3;
+					n->win_null_treatment = $2;
 					$$ = (Node *) n;
 				}
 			| func_expr_common_subexpr
@@ -14096,6 +14109,11 @@ window_definition:
 				}
 		;
 
+null_treatment:
+			IGNORE_P NULLS_P	{ $$ = NULL_TREATMENT_IGNORE; }
+			| RESPECT NULLS_P	{ $$ = NULL_TREATMENT_RESPECT; }
+		;
+
 over_clause: OVER window_specification
 				{ $$ = $2; }
 			| OVER ColId
@@ -15177,6 +15195,7 @@ unreserved_keyword:
 			| HOUR_P
 			| IDENTITY_P
 			| IF_P
+			| IGNORE_P
 			| IMMEDIATE
 			| IMMUTABLE
 			| IMPLICIT_P
@@ -15283,6 +15302,7 @@ unreserved_keyword:
 			| REPLACE
 			| REPLICA
 			| RESET
+			| RESPECT
 			| RESTART
 			| RESTRICT
 			| RETURNS
diff --git a/src/backend/parser/parse_func.c b/src/backend/parser/parse_func.c
index 23ac2a2fe6..b42850f91e 100644
--- a/src/backend/parser/parse_func.c
+++ b/src/backend/parser/parse_func.c
@@ -97,6 +97,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 	bool		agg_distinct = (fn ? fn->agg_distinct : false);
 	bool		func_variadic = (fn ? fn->func_variadic : false);
 	CoercionForm funcformat = (fn ? fn->funcformat : COERCE_EXPLICIT_CALL);
+	NullTreatment	win_null_treatment = (fn ? fn->win_null_treatment : NULL_TREATMENT_NONE);
 	bool		could_be_projection;
 	Oid			rettype;
 	Oid			funcid;
@@ -108,6 +109,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 	Oid		   *declared_arg_types;
 	List	   *argnames;
 	List	   *argdefaults;
+	bool		null_treatment;
 	Node	   *retval;
 	bool		retset;
 	int			nvargs;
@@ -267,7 +269,8 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 							   !func_variadic, true,
 							   &funcid, &rettype, &retset,
 							   &nvargs, &vatype,
-							   &declared_arg_types, &argdefaults);
+							   &declared_arg_types, &argdefaults,
+							   &null_treatment);
 
 	cancel_parser_errposition_callback(&pcbstate);
 
@@ -507,6 +510,13 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 						 errmsg("%s is not an ordered-set aggregate, so it cannot have WITHIN GROUP",
 								NameListToString(funcname)),
 						 parser_errposition(pstate, location)));
+
+			/* It also can't treat nulls as a window function */
+			if (over && win_null_treatment != NULL_TREATMENT_NONE)
+				ereport(ERROR,
+						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+						 errmsg("aggregate functions do not accept RESPECT/IGNORE NULLS"),
+						 parser_errposition(pstate, location)));
 		}
 	}
 	else if (fdresult == FUNCDETAIL_WINDOWFUNC)
@@ -527,6 +537,13 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 					 errmsg("window function %s cannot have WITHIN GROUP",
 							NameListToString(funcname)),
 					 parser_errposition(pstate, location)));
+
+		if (!null_treatment && win_null_treatment != NULL_TREATMENT_NONE)
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("window function %s does not accept RESPECT/IGNORE NULLS",
+							NameListToString(funcname)),
+					 parser_errposition(pstate, location)));
 	}
 	else if (fdresult == FUNCDETAIL_COERCION)
 	{
@@ -826,6 +843,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 		wfunc->winstar = agg_star;
 		wfunc->winagg = (fdresult == FUNCDETAIL_AGGREGATE);
 		wfunc->aggfilter = agg_filter;
+		wfunc->winnulltreatment = win_null_treatment;
 		wfunc->location = location;
 
 		/*
@@ -1396,7 +1414,8 @@ func_get_detail(List *funcname,
 				int *nvargs,	/* return value */
 				Oid *vatype,	/* return value */
 				Oid **true_typeids, /* return value */
-				List **argdefaults) /* optional return value */
+				List **argdefaults, /* optional return value */
+				bool *null_treatment) /* optional return value */
 {
 	FuncCandidateList raw_candidates;
 	FuncCandidateList best_candidate;
@@ -1410,6 +1429,8 @@ func_get_detail(List *funcname,
 	*true_typeids = NULL;
 	if (argdefaults)
 		*argdefaults = NIL;
+	if (null_treatment)
+		*null_treatment = NULL_TREATMENT_NONE;
 
 	/* Get list of possible candidates from namespace search */
 	raw_candidates = FuncnameGetCandidates(funcname, nargs, fargnames,
@@ -1687,6 +1708,8 @@ func_get_detail(List *funcname,
 				*argdefaults = defaults;
 			}
 		}
+		if (null_treatment)
+			*null_treatment = pform->pronulltreatment;
 
 		switch (pform->prokind)
 		{
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 7d4443e807..9e41b61c08 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -2660,6 +2660,9 @@ pg_get_functiondef(PG_FUNCTION_ARGS)
 
 	if (proc->prokind == PROKIND_WINDOW)
 		appendStringInfoString(&buf, " WINDOW");
+	if (proc->pronulltreatment)
+		appendStringInfoString(&buf, " TREAT NULLS");
+
 	switch (proc->provolatile)
 	{
 		case PROVOLATILE_IMMUTABLE:
@@ -9474,7 +9477,12 @@ get_windowfunc_expr(WindowFunc *wfunc, deparse_context *context)
 		get_rule_expr((Node *) wfunc->aggfilter, context, false);
 	}
 
-	appendStringInfoString(buf, ") OVER ");
+	if (wfunc->winnulltreatment == NULL_TREATMENT_IGNORE)
+		appendStringInfoString(buf, ") IGNORE NULLS OVER ");
+	else if (wfunc->winnulltreatment == NULL_TREATMENT_RESPECT)
+		appendStringInfoString(buf, ") RESPECT NULLS OVER ");
+	else
+		appendStringInfoString(buf, ") OVER ");
 
 	foreach(l, context->windowClause)
 	{
@@ -11227,7 +11235,7 @@ generate_function_name(Oid funcid, int nargs, List *argnames, Oid *argtypes,
 								   !use_variadic, true,
 								   &p_funcid, &p_rettype,
 								   &p_retset, &p_nvargs, &p_vatype,
-								   &p_true_typeids, NULL);
+								   &p_true_typeids, NULL, NULL);
 	else
 	{
 		p_result = FUNCDETAIL_NOTFOUND;
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 139f4a08bd..50c7b47be2 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -9770,33 +9770,42 @@
   proargtypes => 'int4', prosrc => 'window_ntile' },
 { oid => '3106', descr => 'fetch the preceding row value',
   proname => 'lag', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_lag' },
+  proargtypes => 'anyelement', prosrc => 'window_lag',
+  pronulltreatment => 't' },
 { oid => '3107', descr => 'fetch the Nth preceding row value',
   proname => 'lag', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_lag_with_offset' },
+  proargtypes => 'anyelement int4', prosrc => 'window_lag_with_offset',
+  pronulltreatment => 't' },
 { oid => '3108', descr => 'fetch the Nth preceding row value with default',
   proname => 'lag', prokind => 'w', prorettype => 'anycompatible',
   proargtypes => 'anycompatible int4 anycompatible',
-  prosrc => 'window_lag_with_offset_and_default' },
+  prosrc => 'window_lag_with_offset_and_default',
+  pronulltreatment => 't' },
 { oid => '3109', descr => 'fetch the following row value',
   proname => 'lead', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_lead' },
+  proargtypes => 'anyelement', prosrc => 'window_lead',
+  pronulltreatment => 't' },
 { oid => '3110', descr => 'fetch the Nth following row value',
   proname => 'lead', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_lead_with_offset' },
+  proargtypes => 'anyelement int4', prosrc => 'window_lead_with_offset',
+  pronulltreatment => 't' },
 { oid => '3111', descr => 'fetch the Nth following row value with default',
   proname => 'lead', prokind => 'w', prorettype => 'anycompatible',
   proargtypes => 'anycompatible int4 anycompatible',
-  prosrc => 'window_lead_with_offset_and_default' },
+  prosrc => 'window_lead_with_offset_and_default',
+  pronulltreatment => 't' },
 { oid => '3112', descr => 'fetch the first row value',
   proname => 'first_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_first_value' },
+  proargtypes => 'anyelement', prosrc => 'window_first_value',
+  pronulltreatment => 't' },
 { oid => '3113', descr => 'fetch the last row value',
   proname => 'last_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_last_value' },
+  proargtypes => 'anyelement', prosrc => 'window_last_value',
+  pronulltreatment => 't' },
 { oid => '3114', descr => 'fetch the Nth row value',
   proname => 'nth_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_nth_value' },
+  proargtypes => 'anyelement int4', prosrc => 'window_nth_value',
+  pronulltreatment => 't' },
 
 # functions for range types
 { oid => '3832', descr => 'I/O',
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index f8e6dea22d..31d1dfd465 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -67,6 +67,9 @@ CATALOG(pg_proc,1255,ProcedureRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(81,Proce
 	/* strict with respect to NULLs? */
 	bool		proisstrict BKI_DEFAULT(t);
 
+	/* can handle IGNORE/RESPECT NULLS? (must be window function) */
+	bool		pronulltreatment BKI_DEFAULT(f);
+
 	/* returns a set? */
 	bool		proretset BKI_DEFAULT(f);
 
@@ -198,6 +201,7 @@ extern ObjectAddress ProcedureCreate(const char *procedureName,
 									 bool security_definer,
 									 bool isLeakProof,
 									 bool isStrict,
+									 bool null_treatment,
 									 char volatility,
 									 char parallel,
 									 oidvector *parameterTypes,
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 48a79a7657..c3dd64d96d 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -357,6 +357,7 @@ typedef struct FuncCall
 	bool		agg_distinct;	/* arguments were labeled DISTINCT */
 	bool		func_variadic;	/* last argument was labeled VARIADIC */
 	CoercionForm funcformat;	/* how to display this node */
+	NullTreatment	win_null_treatment;	/* IGNORE NULLS or RESPECT NULLS? */
 	int			location;		/* token location, or -1 if unknown */
 } FuncCall;
 
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index dd85908fe2..6426c07777 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -52,6 +52,13 @@ typedef enum OnCommitAction
 	ONCOMMIT_DROP				/* ON COMMIT DROP */
 } OnCommitAction;
 
+typedef enum NullTreatment
+{
+	NULL_TREATMENT_NONE = 0,
+	NULL_TREATMENT_RESPECT,
+	NULL_TREATMENT_IGNORE
+} NullTreatment;
+
 /*
  * RangeVar - range variable, used in FROM clauses
  *
@@ -387,6 +394,7 @@ typedef struct WindowFunc
 	Index		winref;			/* index of associated WindowClause */
 	bool		winstar;		/* true if argument list was really '*' */
 	bool		winagg;			/* is function a simple aggregate? */
+	NullTreatment	winnulltreatment;	/* can accept RESPECT/IGNORE NULLS? */
 	int			location;		/* token location, or -1 if unknown */
 } WindowFunc;
 
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 71dcdf2889..b288422fda 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -190,6 +190,7 @@ PG_KEYWORD("hold", HOLD, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("hour", HOUR_P, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("identity", IDENTITY_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("if", IF_P, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("ignore", IGNORE_P, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("ilike", ILIKE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("immediate", IMMEDIATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("immutable", IMMUTABLE, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -342,6 +343,7 @@ PG_KEYWORD("repeatable", REPEATABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("replace", REPLACE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("replica", REPLICA, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("reset", RESET, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("respect", RESPECT, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("restart", RESTART, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("restrict", RESTRICT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("returning", RETURNING, RESERVED_KEYWORD, AS_LABEL)
diff --git a/src/include/parser/parse_func.h b/src/include/parser/parse_func.h
index dd189f5452..ead6241525 100644
--- a/src/include/parser/parse_func.h
+++ b/src/include/parser/parse_func.h
@@ -41,7 +41,8 @@ extern FuncDetailCode func_get_detail(List *funcname,
 									  bool expand_variadic, bool expand_defaults,
 									  Oid *funcid, Oid *rettype,
 									  bool *retset, int *nvargs, Oid *vatype,
-									  Oid **true_typeids, List **argdefaults);
+									  Oid **true_typeids, List **argdefaults,
+									  bool *null_treatment);
 
 extern int	func_match_argtypes(int nargs,
 								Oid *input_typeids,
diff --git a/src/test/regress/expected/create_function_3.out b/src/test/regress/expected/create_function_3.out
index ce508ae1dc..0311f8ecc9 100644
--- a/src/test/regress/expected/create_function_3.out
+++ b/src/test/regress/expected/create_function_3.out
@@ -122,6 +122,12 @@ SELECT proname, prosecdef FROM pg_proc
  functest_c_3 | t
 (3 rows)
 
+--
+-- TREAT NULLS
+--
+CREATE FUNCTION functest_D_1(integer) RETURNS integer LANGUAGE 'sql'
+       TREAT NULLS AS 'SELECT $1';
+ERROR:  cannot set null treatment on a non-window function
 --
 -- LEAKPROOF
 --
@@ -298,6 +304,8 @@ CREATE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL AS 'SELECT $1';
 CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL WINDOW AS 'SELECT $1';
 ERROR:  cannot change routine kind
 DETAIL:  "functest1" is a function.
+CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL TREAT NULLS AS 'SELECT $1';
+ERROR:  cannot set null treatment on a non-window function
 CREATE OR REPLACE PROCEDURE functest1(a int) LANGUAGE SQL AS 'SELECT $1';
 ERROR:  cannot change routine kind
 DETAIL:  "functest1" is a function.
diff --git a/src/test/regress/expected/create_procedure.out b/src/test/regress/expected/create_procedure.out
index 3838fa2324..f81f9b79cc 100644
--- a/src/test/regress/expected/create_procedure.out
+++ b/src/test/regress/expected/create_procedure.out
@@ -174,6 +174,10 @@ CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT INTO cp_test VALUES (
 ERROR:  invalid attribute in procedure definition
 LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT I...
                                                ^
+CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
+ERROR:  invalid attribute in procedure definition
+LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INS...
+                                               ^
 CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 ERROR:  invalid attribute in procedure definition
 LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT I...
diff --git a/src/test/regress/expected/misc_sanity.out b/src/test/regress/expected/misc_sanity.out
index d40afeef78..8615d78075 100644
--- a/src/test/regress/expected/misc_sanity.out
+++ b/src/test/regress/expected/misc_sanity.out
@@ -109,3 +109,13 @@ ORDER BY 1, 2;
  pg_largeobject_metadata | lomacl        | aclitem[]
 (11 rows)
 
+-- **************** pg_class ****************
+-- Look for non-window functions with null treatment (there should be none)
+SELECT proname, prokind, pronulltreatment
+FROM pg_proc
+WHERE pronulltreatment AND prokind <> 'w'
+ORDER BY oid;
+ proname | prokind | pronulltreatment 
+---------+---------+------------------
+(0 rows)
+
diff --git a/src/test/regress/expected/window.out b/src/test/regress/expected/window.out
index 19e2ac518a..3bd9584c6c 100644
--- a/src/test/regress/expected/window.out
+++ b/src/test/regress/expected/window.out
@@ -4063,3 +4063,214 @@ SELECT * FROM pg_temp.f(2);
  {5}
 (5 rows)
 
+-- IGNORE NULLS tests
+CREATE TEMPORARY TABLE planets (
+    name text,
+    orbit integer
+);
+INSERT INTO planets VALUES
+  ('mercury', 88),
+  ('venus', 224),
+  ('earth', NULL),
+  ('mars', NULL),
+  ('jupiter', 4332),
+  ('saturn', 24491),
+  ('uranus', NULL),
+  ('neptune', 60182),
+  ('pluto', 90560),
+  ('xyzzy', NULL);
+-- test ruleutils
+CREATE VIEW planets_view AS
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+NOTICE:  view "planets_view" will be a temporary view
+SELECT pg_get_viewdef('planets_view');
+                       pg_get_viewdef                        
+-------------------------------------------------------------
+  SELECT planets.name,                                      +
+     planets.orbit,                                         +
+     lag(planets.orbit) OVER w AS lag,                      +
+     lag(planets.orbit) RESPECT NULLS OVER w AS lag_respect,+
+     lag(planets.orbit) IGNORE NULLS OVER w AS lag_ignore   +
+    FROM planets                                            +
+   WINDOW w AS (ORDER BY planets.name);
+(1 row)
+
+-- lag
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+  name   | orbit |  lag  | lag_respect | lag_ignore 
+---------+-------+-------+-------------+------------
+ earth   |       |       |             |           
+ jupiter |  4332 |       |             |           
+ mars    |       |  4332 |        4332 |       4332
+ mercury |    88 |       |             |       4332
+ neptune | 60182 |    88 |          88 |         88
+ pluto   | 90560 | 60182 |       60182 |      60182
+ saturn  | 24491 | 90560 |       90560 |      90560
+ uranus  |       | 24491 |       24491 |      24491
+ venus   |   224 |       |             |      24491
+ xyzzy   |       |   224 |         224 |        224
+(10 rows)
+
+-- lead
+SELECT name,
+       orbit,
+       lead(orbit) OVER w AS lead,
+       lead(orbit) RESPECT NULLS OVER w AS lead_respect,
+       lead(orbit) IGNORE NULLS OVER w AS lead_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+  name   | orbit | lead  | lead_respect | lead_ignore 
+---------+-------+-------+--------------+-------------
+ earth   |       |  4332 |         4332 |        4332
+ jupiter |  4332 |       |              |          88
+ mars    |       |    88 |           88 |          88
+ mercury |    88 | 60182 |        60182 |       60182
+ neptune | 60182 | 90560 |        90560 |       90560
+ pluto   | 90560 | 24491 |        24491 |       24491
+ saturn  | 24491 |       |              |         224
+ uranus  |       |   224 |          224 |         224
+ venus   |   224 |       |              |            
+ xyzzy   |       |       |              |            
+(10 rows)
+
+-- first_value
+SELECT name,
+       orbit,
+       first_value(orbit) RESPECT NULLS OVER w1,
+       first_value(orbit) IGNORE NULLS OVER w1,
+       first_value(orbit) RESPECT NULLS OVER w2,
+       first_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | first_value | first_value | first_value | first_value 
+---------+-------+-------------+-------------+-------------+-------------
+ earth   |       |             |        4332 |             |        4332
+ jupiter |  4332 |             |        4332 |             |        4332
+ mars    |       |             |        4332 |             |        4332
+ mercury |    88 |             |        4332 |        4332 |        4332
+ neptune | 60182 |             |        4332 |             |          88
+ pluto   | 90560 |             |        4332 |          88 |          88
+ saturn  | 24491 |             |        4332 |       60182 |       60182
+ uranus  |       |             |        4332 |       90560 |       90560
+ venus   |   224 |             |        4332 |       24491 |       24491
+ xyzzy   |       |             |        4332 |             |         224
+(10 rows)
+
+-- nth_value
+SELECT name,
+       orbit,
+       nth_value(orbit, 2) RESPECT NULLS OVER w1,
+       nth_value(orbit, 2) IGNORE NULLS OVER w1,
+       nth_value(orbit, 2) RESPECT NULLS OVER w2,
+       nth_value(orbit, 2) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | nth_value | nth_value | nth_value | nth_value 
+---------+-------+-----------+-----------+-----------+-----------
+ earth   |       |      4332 |        88 |      4332 |          
+ jupiter |  4332 |      4332 |        88 |      4332 |        88
+ mars    |       |      4332 |        88 |      4332 |        88
+ mercury |    88 |      4332 |        88 |           |        88
+ neptune | 60182 |      4332 |        88 |        88 |     60182
+ pluto   | 90560 |      4332 |        88 |     60182 |     60182
+ saturn  | 24491 |      4332 |        88 |     90560 |     90560
+ uranus  |       |      4332 |        88 |     24491 |     24491
+ venus   |   224 |      4332 |        88 |           |       224
+ xyzzy   |       |      4332 |        88 |       224 |          
+(10 rows)
+
+-- last_value
+SELECT name,
+       orbit,
+       last_value(orbit) RESPECT NULLS OVER w1,
+       last_value(orbit) IGNORE NULLS OVER w1,
+       last_value(orbit) RESPECT NULLS OVER w2,
+       last_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | last_value | last_value | last_value | last_value 
+---------+-------+------------+------------+------------+------------
+ earth   |       |            |        224 |            |       4332
+ jupiter |  4332 |            |        224 |         88 |         88
+ mars    |       |            |        224 |      60182 |      60182
+ mercury |    88 |            |        224 |      90560 |      90560
+ neptune | 60182 |            |        224 |      24491 |      24491
+ pluto   | 90560 |            |        224 |            |      24491
+ saturn  | 24491 |            |        224 |        224 |        224
+ uranus  |       |            |        224 |            |        224
+ venus   |   224 |            |        224 |            |        224
+ xyzzy   |       |            |        224 |            |        224
+(10 rows)
+
+-- window function without null treatment
+SELECT row_number() OVER (ORDER BY name) FROM planets;
+ row_number 
+------------
+          1
+          2
+          3
+          4
+          5
+          6
+          7
+          8
+          9
+         10
+(10 rows)
+
+SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM planets; -- fails
+ERROR:  window function row_number does not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM ...
+               ^
+SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM planets; -- fails
+ERROR:  window function row_number does not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM p...
+               ^
+-- regular aggregate
+SELECT sum(orbit) OVER () FROM planets;
+  sum   
+--------
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+(10 rows)
+
+SELECT sum(orbit) RESPECT NULLS OVER () FROM planets; -- fails
+ERROR:  aggregate functions do not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT sum(orbit) RESPECT NULLS OVER () FROM planets;
+               ^
+SELECT sum(orbit) IGNORE NULLS OVER () FROM planets; -- fails
+ERROR:  aggregate functions do not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT sum(orbit) IGNORE NULLS OVER () FROM planets;
+               ^
+--cleanup
+DROP TABLE planets CASCADE;
+NOTICE:  drop cascades to view planets_view
diff --git a/src/test/regress/sql/create_function_3.sql b/src/test/regress/sql/create_function_3.sql
index bd108a918f..f7fe984e58 100644
--- a/src/test/regress/sql/create_function_3.sql
+++ b/src/test/regress/sql/create_function_3.sql
@@ -82,6 +82,12 @@ SELECT proname, prosecdef FROM pg_proc
                      'functest_C_2'::regproc,
                      'functest_C_3'::regproc) ORDER BY proname;
 
+--
+-- TREAT NULLS
+--
+CREATE FUNCTION functest_D_1(integer) RETURNS integer LANGUAGE 'sql'
+       TREAT NULLS AS 'SELECT $1';
+
 --
 -- LEAKPROOF
 --
@@ -190,6 +196,7 @@ DROP FUNCTION functest_b_2;  -- error, ambiguous
 
 CREATE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL AS 'SELECT $1';
 CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL WINDOW AS 'SELECT $1';
+CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL TREAT NULLS AS 'SELECT $1';
 CREATE OR REPLACE PROCEDURE functest1(a int) LANGUAGE SQL AS 'SELECT $1';
 DROP FUNCTION functest1(a int);
 
diff --git a/src/test/regress/sql/create_procedure.sql b/src/test/regress/sql/create_procedure.sql
index 2ef1c82cea..188f5f85a9 100644
--- a/src/test/regress/sql/create_procedure.sql
+++ b/src/test/regress/sql/create_procedure.sql
@@ -130,6 +130,7 @@ CALL version();  -- error: not a procedure
 CALL sum(1);  -- error: not a procedure
 
 CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
+CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 
 ALTER PROCEDURE ptest1(text) STRICT;
diff --git a/src/test/regress/sql/misc_sanity.sql b/src/test/regress/sql/misc_sanity.sql
index 3ce32e4725..ccb4f008d9 100644
--- a/src/test/regress/sql/misc_sanity.sql
+++ b/src/test/regress/sql/misc_sanity.sql
@@ -94,3 +94,12 @@ WHERE c.oid < 16384 AND
       relkind = 'r' AND
       attstorage != 'p'
 ORDER BY 1, 2;
+
+-- **************** pg_class ****************
+
+-- Look for non-window functions with null treatment (there should be none)
+
+SELECT proname, prokind, pronulltreatment
+FROM pg_proc
+WHERE pronulltreatment AND prokind <> 'w'
+ORDER BY oid;
diff --git a/src/test/regress/sql/window.sql b/src/test/regress/sql/window.sql
index eae5fa6017..a021ed3544 100644
--- a/src/test/regress/sql/window.sql
+++ b/src/test/regress/sql/window.sql
@@ -1328,3 +1328,104 @@ $$ LANGUAGE SQL STABLE;
 
 EXPLAIN (costs off) SELECT * FROM pg_temp.f(2);
 SELECT * FROM pg_temp.f(2);
+
+
+-- IGNORE NULLS tests
+
+CREATE TEMPORARY TABLE planets (
+    name text,
+    orbit integer
+);
+
+INSERT INTO planets VALUES
+  ('mercury', 88),
+  ('venus', 224),
+  ('earth', NULL),
+  ('mars', NULL),
+  ('jupiter', 4332),
+  ('saturn', 24491),
+  ('uranus', NULL),
+  ('neptune', 60182),
+  ('pluto', 90560),
+  ('xyzzy', NULL);
+
+-- test ruleutils
+CREATE VIEW planets_view AS
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+SELECT pg_get_viewdef('planets_view');
+
+-- lag
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+
+-- lead
+SELECT name,
+       orbit,
+       lead(orbit) OVER w AS lead,
+       lead(orbit) RESPECT NULLS OVER w AS lead_respect,
+       lead(orbit) IGNORE NULLS OVER w AS lead_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+
+-- first_value
+SELECT name,
+       orbit,
+       first_value(orbit) RESPECT NULLS OVER w1,
+       first_value(orbit) IGNORE NULLS OVER w1,
+       first_value(orbit) RESPECT NULLS OVER w2,
+       first_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- nth_value
+SELECT name,
+       orbit,
+       nth_value(orbit, 2) RESPECT NULLS OVER w1,
+       nth_value(orbit, 2) IGNORE NULLS OVER w1,
+       nth_value(orbit, 2) RESPECT NULLS OVER w2,
+       nth_value(orbit, 2) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- last_value
+SELECT name,
+       orbit,
+       last_value(orbit) RESPECT NULLS OVER w1,
+       last_value(orbit) IGNORE NULLS OVER w1,
+       last_value(orbit) RESPECT NULLS OVER w2,
+       last_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- window function without null treatment
+SELECT row_number() OVER (ORDER BY name) FROM planets;
+SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM planets; -- fails
+SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM planets; -- fails
+
+-- regular aggregate
+SELECT sum(orbit) OVER () FROM planets;
+SELECT sum(orbit) RESPECT NULLS OVER () FROM planets; -- fails
+SELECT sum(orbit) IGNORE NULLS OVER () FROM planets; -- fails
+
+--cleanup
+DROP TABLE planets CASCADE;

From 7c8ae2cac7b2157f48e9e15c863eccde29a539b4 Mon Sep 17 00:00:00 2001
From: David Fetter <david@fetter.org>
Date: Tue, 22 Dec 2020 19:47:35 -0800
Subject: [PATCH v2] Vik's <NULL treatment> patch
To: hackers
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="------------2.29.2"

This is a multi-part message in MIME format.
--------------2.29.2
Content-Type: text/plain; charset=UTF-8; format=fixed
Content-Transfer-Encoding: 8bit


diff --git doc/src/sgml/func.sgml doc/src/sgml/func.sgml
index 5021ac1ca9..0e877c48df 100644
--- doc/src/sgml/func.sgml
+++ doc/src/sgml/func.sgml
@@ -20373,6 +20373,14 @@ SELECT count(*) FROM sometable;
    about frame specifications.
   </para>
 
+  <para>
+   The functions <function>lead</function>, <function>lag</function>,
+   <function>first_value</function>, <function>last_value</function>, and
+   <function>nth_value</function> accept a null treatment option which is
+   <literal>RESPECT NULLS</literal> or <literal>IGNORE NULLS</literal>.
+   If this option is not specified, the default is <literal>RESPECT NULLS</literal>.
+  </para>
+
   <para>
    When an aggregate function is used as a window function, it aggregates
    over the rows within the current row's window frame.
@@ -20386,14 +20394,9 @@ SELECT count(*) FROM sometable;
 
   <note>
    <para>
-    The SQL standard defines a <literal>RESPECT NULLS</literal> or
-    <literal>IGNORE NULLS</literal> option for <function>lead</function>, <function>lag</function>,
-    <function>first_value</function>, <function>last_value</function>, and
-    <function>nth_value</function>.  This is not implemented in
-    <productname>PostgreSQL</productname>: the behavior is always the
-    same as the standard's default, namely <literal>RESPECT NULLS</literal>.
-    Likewise, the standard's <literal>FROM FIRST</literal> or <literal>FROM LAST</literal>
-    option for <function>nth_value</function> is not implemented: only the
+    The SQL standard defines a <literal>FROM FIRST</literal> or <literal>FROM LAST</literal>
+    option for <function>nth_value</function>.  This is not implemented in
+    <productname>PostgreSQL</productname>: only the
     default <literal>FROM FIRST</literal> behavior is supported.  (You can achieve
     the result of <literal>FROM LAST</literal> by reversing the <literal>ORDER BY</literal>
     ordering.)
diff --git doc/src/sgml/ref/create_function.sgml doc/src/sgml/ref/create_function.sgml
index 3c1eaea651..31e08c26b4 100644
--- doc/src/sgml/ref/create_function.sgml
+++ doc/src/sgml/ref/create_function.sgml
@@ -28,6 +28,7 @@ CREATE [ OR REPLACE ] FUNCTION
   { LANGUAGE <replaceable class="parameter">lang_name</replaceable>
     | TRANSFORM { FOR TYPE <replaceable class="parameter">type_name</replaceable> } [, ... ]
     | WINDOW
+    | TREAT NULLS
     | IMMUTABLE | STABLE | VOLATILE | [ NOT ] LEAKPROOF
     | CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
     | [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
@@ -293,6 +294,17 @@ CREATE [ OR REPLACE ] FUNCTION
      </listitem>
     </varlistentry>
 
+    <varlistentry>
+     <term><literal>TREAT NULLS</literal></term>
+
+     <listitem>
+      <para><literal>TREAT NULLS</literal> indicates that the function is able
+      to handle the <literal>RESPECT NULLS</literal> and <literal>IGNORE
+      NULLS</literal> options.  Only window functions may specify this.
+      </para>
+     </listitem>
+    </varlistentry>
+
     <varlistentry>
      <term><literal>IMMUTABLE</literal></term>
      <term><literal>STABLE</literal></term>
diff --git doc/src/sgml/syntax.sgml doc/src/sgml/syntax.sgml
index d66560b587..103595d21b 100644
--- doc/src/sgml/syntax.sgml
+++ doc/src/sgml/syntax.sgml
@@ -1766,6 +1766,8 @@ FROM generate_series(1,10) AS s(i);
     The syntax of a window function call is one of the following:
 
 <synopsis>
+<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ RESPECT NULLS | IGNORE NULLS ] OVER <replaceable>window_name</replaceable>
+<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ RESPECT NULLS | IGNORE NULLS ] OVER ( <replaceable class="parameter">window_definition</replaceable> )
 <replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER <replaceable>window_name</replaceable>
 <replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER ( <replaceable class="parameter">window_definition</replaceable> )
 <replaceable>function_name</replaceable> ( * ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER <replaceable>window_name</replaceable>
@@ -1779,6 +1781,18 @@ FROM generate_series(1,10) AS s(i);
 [ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [ NULLS { FIRST | LAST } ] [, ...] ]
 [ <replaceable class="parameter">frame_clause</replaceable> ]
 </synopsis>
+   </para>
+
+   <note>
+    <para>
+     The versions with <literal>RESPECT NULLS</literal> or <literal>IGNORE
+     NULLS</literal> only apply to true window functions, whereas the versions
+     with <literal>FILTER</literal> only apply to aggregate functions used as
+     window functions.
+    </para>
+   </note>
+
+   <para>
     The optional <replaceable class="parameter">frame_clause</replaceable>
     can be one of
 <synopsis>
diff --git src/include/catalog/pg_proc.dat src/include/catalog/pg_proc.dat
index 139f4a08bd..50c7b47be2 100644
--- src/include/catalog/pg_proc.dat
+++ src/include/catalog/pg_proc.dat
@@ -9770,33 +9770,42 @@
   proargtypes => 'int4', prosrc => 'window_ntile' },
 { oid => '3106', descr => 'fetch the preceding row value',
   proname => 'lag', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_lag' },
+  proargtypes => 'anyelement', prosrc => 'window_lag',
+  pronulltreatment => 't' },
 { oid => '3107', descr => 'fetch the Nth preceding row value',
   proname => 'lag', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_lag_with_offset' },
+  proargtypes => 'anyelement int4', prosrc => 'window_lag_with_offset',
+  pronulltreatment => 't' },
 { oid => '3108', descr => 'fetch the Nth preceding row value with default',
   proname => 'lag', prokind => 'w', prorettype => 'anycompatible',
   proargtypes => 'anycompatible int4 anycompatible',
-  prosrc => 'window_lag_with_offset_and_default' },
+  prosrc => 'window_lag_with_offset_and_default',
+  pronulltreatment => 't' },
 { oid => '3109', descr => 'fetch the following row value',
   proname => 'lead', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_lead' },
+  proargtypes => 'anyelement', prosrc => 'window_lead',
+  pronulltreatment => 't' },
 { oid => '3110', descr => 'fetch the Nth following row value',
   proname => 'lead', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_lead_with_offset' },
+  proargtypes => 'anyelement int4', prosrc => 'window_lead_with_offset',
+  pronulltreatment => 't' },
 { oid => '3111', descr => 'fetch the Nth following row value with default',
   proname => 'lead', prokind => 'w', prorettype => 'anycompatible',
   proargtypes => 'anycompatible int4 anycompatible',
-  prosrc => 'window_lead_with_offset_and_default' },
+  prosrc => 'window_lead_with_offset_and_default',
+  pronulltreatment => 't' },
 { oid => '3112', descr => 'fetch the first row value',
   proname => 'first_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_first_value' },
+  proargtypes => 'anyelement', prosrc => 'window_first_value',
+  pronulltreatment => 't' },
 { oid => '3113', descr => 'fetch the last row value',
   proname => 'last_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_last_value' },
+  proargtypes => 'anyelement', prosrc => 'window_last_value',
+  pronulltreatment => 't' },
 { oid => '3114', descr => 'fetch the Nth row value',
   proname => 'nth_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_nth_value' },
+  proargtypes => 'anyelement int4', prosrc => 'window_nth_value',
+  pronulltreatment => 't' },
 
 # functions for range types
 { oid => '3832', descr => 'I/O',
diff --git src/include/catalog/pg_proc.h src/include/catalog/pg_proc.h
index f8e6dea22d..31d1dfd465 100644
--- src/include/catalog/pg_proc.h
+++ src/include/catalog/pg_proc.h
@@ -67,6 +67,9 @@ CATALOG(pg_proc,1255,ProcedureRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(81,Proce
 	/* strict with respect to NULLs? */
 	bool		proisstrict BKI_DEFAULT(t);
 
+	/* can handle IGNORE/RESPECT NULLS? (must be window function) */
+	bool		pronulltreatment BKI_DEFAULT(f);
+
 	/* returns a set? */
 	bool		proretset BKI_DEFAULT(f);
 
@@ -198,6 +201,7 @@ extern ObjectAddress ProcedureCreate(const char *procedureName,
 									 bool security_definer,
 									 bool isLeakProof,
 									 bool isStrict,
+									 bool null_treatment,
 									 char volatility,
 									 char parallel,
 									 oidvector *parameterTypes,
diff --git src/include/nodes/parsenodes.h src/include/nodes/parsenodes.h
index 48a79a7657..c3dd64d96d 100644
--- src/include/nodes/parsenodes.h
+++ src/include/nodes/parsenodes.h
@@ -357,6 +357,7 @@ typedef struct FuncCall
 	bool		agg_distinct;	/* arguments were labeled DISTINCT */
 	bool		func_variadic;	/* last argument was labeled VARIADIC */
 	CoercionForm funcformat;	/* how to display this node */
+	NullTreatment	win_null_treatment;	/* IGNORE NULLS or RESPECT NULLS? */
 	int			location;		/* token location, or -1 if unknown */
 } FuncCall;
 
diff --git src/include/nodes/primnodes.h src/include/nodes/primnodes.h
index dd85908fe2..6426c07777 100644
--- src/include/nodes/primnodes.h
+++ src/include/nodes/primnodes.h
@@ -52,6 +52,13 @@ typedef enum OnCommitAction
 	ONCOMMIT_DROP				/* ON COMMIT DROP */
 } OnCommitAction;
 
+typedef enum NullTreatment
+{
+	NULL_TREATMENT_NONE = 0,
+	NULL_TREATMENT_RESPECT,
+	NULL_TREATMENT_IGNORE
+} NullTreatment;
+
 /*
  * RangeVar - range variable, used in FROM clauses
  *
@@ -387,6 +394,7 @@ typedef struct WindowFunc
 	Index		winref;			/* index of associated WindowClause */
 	bool		winstar;		/* true if argument list was really '*' */
 	bool		winagg;			/* is function a simple aggregate? */
+	NullTreatment	winnulltreatment;	/* can accept RESPECT/IGNORE NULLS? */
 	int			location;		/* token location, or -1 if unknown */
 } WindowFunc;
 
diff --git src/include/parser/kwlist.h src/include/parser/kwlist.h
index 71dcdf2889..b288422fda 100644
--- src/include/parser/kwlist.h
+++ src/include/parser/kwlist.h
@@ -190,6 +190,7 @@ PG_KEYWORD("hold", HOLD, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("hour", HOUR_P, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("identity", IDENTITY_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("if", IF_P, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("ignore", IGNORE_P, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("ilike", ILIKE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("immediate", IMMEDIATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("immutable", IMMUTABLE, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -342,6 +343,7 @@ PG_KEYWORD("repeatable", REPEATABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("replace", REPLACE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("replica", REPLICA, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("reset", RESET, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("respect", RESPECT, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("restart", RESTART, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("restrict", RESTRICT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("returning", RETURNING, RESERVED_KEYWORD, AS_LABEL)
diff --git src/include/parser/parse_func.h src/include/parser/parse_func.h
index dd189f5452..ead6241525 100644
--- src/include/parser/parse_func.h
+++ src/include/parser/parse_func.h
@@ -41,7 +41,8 @@ extern FuncDetailCode func_get_detail(List *funcname,
 									  bool expand_variadic, bool expand_defaults,
 									  Oid *funcid, Oid *rettype,
 									  bool *retset, int *nvargs, Oid *vatype,
-									  Oid **true_typeids, List **argdefaults);
+									  Oid **true_typeids, List **argdefaults,
+									  bool *null_treatment);
 
 extern int	func_match_argtypes(int nargs,
 								Oid *input_typeids,
diff --git src/backend/catalog/pg_aggregate.c src/backend/catalog/pg_aggregate.c
index 7664bb6285..fea8778ec8 100644
--- src/backend/catalog/pg_aggregate.c
+++ src/backend/catalog/pg_aggregate.c
@@ -627,6 +627,7 @@ AggregateCreate(const char *aggName,
 									 * definable for agg) */
 							 false, /* isLeakProof */
 							 false, /* isStrict (not needed for agg) */
+							 false, /* null_treatment (not needed for agg) */
 							 PROVOLATILE_IMMUTABLE, /* volatility (not needed
 													 * for agg) */
 							 proparallel,
@@ -848,7 +849,7 @@ lookup_agg_function(List *fnName,
 							   nargs, input_types, false, false,
 							   &fnOid, rettype, &retset,
 							   &nvargs, &vatype,
-							   &true_oid_array, NULL);
+							   &true_oid_array, NULL, NULL);
 
 	/* only valid case is a normal function not returning a set */
 	if (fdresult != FUNCDETAIL_NORMAL || !OidIsValid(fnOid))
diff --git src/backend/catalog/pg_proc.c src/backend/catalog/pg_proc.c
index 1dd9ecc063..2783b0d630 100644
--- src/backend/catalog/pg_proc.c
+++ src/backend/catalog/pg_proc.c
@@ -80,6 +80,7 @@ ProcedureCreate(const char *procedureName,
 				bool security_definer,
 				bool isLeakProof,
 				bool isStrict,
+				bool null_treatment,
 				char volatility,
 				char parallel,
 				oidvector *parameterTypes,
@@ -307,6 +308,7 @@ ProcedureCreate(const char *procedureName,
 	values[Anum_pg_proc_prosecdef - 1] = BoolGetDatum(security_definer);
 	values[Anum_pg_proc_proleakproof - 1] = BoolGetDatum(isLeakProof);
 	values[Anum_pg_proc_proisstrict - 1] = BoolGetDatum(isStrict);
+	values[Anum_pg_proc_pronulltreatment - 1] = BoolGetDatum(null_treatment);
 	values[Anum_pg_proc_proretset - 1] = BoolGetDatum(returnsSet);
 	values[Anum_pg_proc_provolatile - 1] = CharGetDatum(volatility);
 	values[Anum_pg_proc_proparallel - 1] = CharGetDatum(parallel);
@@ -386,6 +388,12 @@ ProcedureCreate(const char *procedureName,
 					  errdetail("\"%s\" is a window function.", procedureName) :
 					  0)));
 
+		/* Not okay to set null treatment if not a window function */
+		if (null_treatment && oldproc->prokind != PROKIND_WINDOW)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+					 errmsg("cannot set null treatment on a non-window function")));
+
 		dropcmd = (prokind == PROKIND_PROCEDURE ? "DROP PROCEDURE" :
 				   prokind == PROKIND_AGGREGATE ? "DROP AGGREGATE" :
 				   "DROP FUNCTION");
diff --git src/backend/catalog/sql_features.txt src/backend/catalog/sql_features.txt
index caa971c435..0615b08858 100644
--- src/backend/catalog/sql_features.txt
+++ src/backend/catalog/sql_features.txt
@@ -508,9 +508,9 @@ T612	Advanced OLAP operations			YES
 T613	Sampling			YES	
 T614	NTILE function			YES	
 T615	LEAD and LAG functions			YES	
-T616	Null treatment option for LEAD and LAG functions			NO	
+T616	Null treatment option for LEAD and LAG functions			YES	
 T617	FIRST_VALUE and LAST_VALUE function			YES	
-T618	NTH_VALUE function			NO	function exists, but some options missing
+T618	NTH_VALUE function			NO	supported except FROM LAST is not implemented
 T619	Nested window functions			NO	
 T620	WINDOW clause: GROUPS option			YES	
 T621	Enhanced numeric functions			YES	
diff --git src/backend/commands/functioncmds.c src/backend/commands/functioncmds.c
index c3ce480c8f..245a768463 100644
--- src/backend/commands/functioncmds.c
+++ src/backend/commands/functioncmds.c
@@ -697,6 +697,7 @@ compute_function_attributes(ParseState *pstate,
 							bool *windowfunc_p,
 							char *volatility_p,
 							bool *strict_p,
+							bool *null_treatment_p,
 							bool *security_definer,
 							bool *leakproof_p,
 							ArrayType **proconfig,
@@ -710,6 +711,7 @@ compute_function_attributes(ParseState *pstate,
 	DefElem    *language_item = NULL;
 	DefElem    *transform_item = NULL;
 	DefElem    *windowfunc_item = NULL;
+	DefElem    *nulltreatment_item = NULL;
 	DefElem    *volatility_item = NULL;
 	DefElem    *strict_item = NULL;
 	DefElem    *security_item = NULL;
@@ -765,6 +767,20 @@ compute_function_attributes(ParseState *pstate,
 						 parser_errposition(pstate, defel->location)));
 			windowfunc_item = defel;
 		}
+		else if (strcmp(defel->defname, "null_treatment") == 0)
+		{
+			if (nulltreatment_item)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 parser_errposition(pstate, defel->location)));
+			if (is_procedure)
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+						 errmsg("invalid attribute in procedure definition"),
+						 parser_errposition(pstate, defel->location)));
+			nulltreatment_item = defel;
+		}
 		else if (compute_common_attribute(pstate,
 										  is_procedure,
 										  defel,
@@ -816,6 +832,14 @@ compute_function_attributes(ParseState *pstate,
 		*volatility_p = interpret_func_volatility(volatility_item);
 	if (strict_item)
 		*strict_p = intVal(strict_item->arg);
+	if (nulltreatment_item)
+	{
+		*null_treatment_p = intVal(nulltreatment_item->arg);
+		if (*null_treatment_p && !*windowfunc_p)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+					 errmsg("cannot set null treatment on a non-window function")));
+	}
 	if (security_item)
 		*security_definer = intVal(security_item->arg);
 	if (leakproof_item)
@@ -941,6 +965,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 				isStrict,
 				security,
 				isLeakProof;
+	bool		null_treatment;
 	char		volatility;
 	ArrayType  *proconfig;
 	float4		procost;
@@ -964,6 +989,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 	/* Set default attributes */
 	isWindowFunc = false;
 	isStrict = false;
+	null_treatment = false;
 	security = false;
 	isLeakProof = false;
 	volatility = PROVOLATILE_VOLATILE;
@@ -979,7 +1005,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 								stmt->options,
 								&as_clause, &language, &transformDefElem,
 								&isWindowFunc, &volatility,
-								&isStrict, &security, &isLeakProof,
+								&isStrict, &null_treatment, &security, &isLeakProof,
 								&proconfig, &procost, &prorows,
 								&prosupport, &parallel);
 
@@ -1159,6 +1185,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 						   security,
 						   isLeakProof,
 						   isStrict,
+						   null_treatment,
 						   volatility,
 						   parallel,
 						   parameterTypes,
diff --git src/backend/commands/typecmds.c src/backend/commands/typecmds.c
index a0a8695b1b..15eb9e9339 100644
--- src/backend/commands/typecmds.c
+++ src/backend/commands/typecmds.c
@@ -1779,6 +1779,7 @@ makeRangeConstructors(const char *name, Oid namespace,
 								 false, /* security_definer */
 								 false, /* leakproof */
 								 false, /* isStrict */
+								 false, /* null_treatment */
 								 PROVOLATILE_IMMUTABLE, /* volatility */
 								 PROPARALLEL_SAFE,	/* parallel safety */
 								 constructorArgTypesVector, /* parameterTypes */
@@ -1843,6 +1844,7 @@ makeMultirangeConstructors(const char *name, Oid namespace,
 							 false, /* security_definer */
 							 false, /* leakproof */
 							 false, /* isStrict */
+							 false, /* null_treatement */
 							 PROVOLATILE_IMMUTABLE, /* volatility */
 							 PROPARALLEL_SAFE,	/* parallel safety */
 							 argtypes,	/* parameterTypes */
@@ -1886,6 +1888,7 @@ makeMultirangeConstructors(const char *name, Oid namespace,
 							 false, /* security_definer */
 							 false, /* leakproof */
 							 true,	/* isStrict */
+							 false,	/* null_treatement */
 							 PROVOLATILE_IMMUTABLE, /* volatility */
 							 PROPARALLEL_SAFE,	/* parallel safety */
 							 argtypes,	/* parameterTypes */
@@ -1926,6 +1929,7 @@ makeMultirangeConstructors(const char *name, Oid namespace,
 							 false, /* security_definer */
 							 false, /* leakproof */
 							 false, /* isStrict */
+							 false, /* null_treatment */
 							 PROVOLATILE_IMMUTABLE, /* volatility */
 							 PROPARALLEL_SAFE,	/* parallel safety */
 							 argtypes,	/* parameterTypes */
diff --git src/backend/executor/nodeWindowAgg.c src/backend/executor/nodeWindowAgg.c
index de58df3d3f..832b40b849 100644
--- src/backend/executor/nodeWindowAgg.c
+++ src/backend/executor/nodeWindowAgg.c
@@ -68,6 +68,7 @@ typedef struct WindowObjectData
 	int			readptr;		/* tuplestore read pointer for this fn */
 	int64		markpos;		/* row that markptr is positioned on */
 	int64		seekpos;		/* row that readptr is positioned on */
+	NullTreatment	null_treatment;	/* RESPECT/IGNORE NULLS? */
 } WindowObjectData;
 
 /*
@@ -2473,6 +2474,7 @@ ExecInitWindowAgg(WindowAgg *node, EState *estate, int eflags)
 			winobj->winstate = winstate;
 			winobj->argstates = wfuncstate->args;
 			winobj->localmem = NULL;
+			winobj->null_treatment = wfunc->winnulltreatment;
 			perfuncstate->winobj = winobj;
 
 			/* It's a real window function, so set up to call it. */
@@ -3173,48 +3175,103 @@ WinGetFuncArgInPartition(WindowObject winobj, int argno,
 	TupleTableSlot *slot;
 	bool		gottuple;
 	int64		abs_pos;
+	bool		ignore_nulls = false;
+	int			target = relpos;
+	int			step;
+	Datum		result;
 
 	Assert(WindowObjectIsValid(winobj));
 	winstate = winobj->winstate;
 	econtext = winstate->ss.ps.ps_ExprContext;
 	slot = winstate->temp_slot_1;
 
-	switch (seektype)
+	/*
+	 * If we're not ignoring nulls, we'll just go straight to the desired row.
+	 * But if we are ignoring nulls, we'll have to step towards the target row
+	 * by row so we need to determine how we get there.
+	 */
+	if (winobj->null_treatment == NULL_TREATMENT_IGNORE)
 	{
-		case WINDOW_SEEK_CURRENT:
-			abs_pos = winstate->currentpos + relpos;
-			break;
-		case WINDOW_SEEK_HEAD:
-			abs_pos = relpos;
-			break;
-		case WINDOW_SEEK_TAIL:
-			spool_tuples(winstate, -1);
-			abs_pos = winstate->spooled_rows - 1 + relpos;
-			break;
-		default:
-			elog(ERROR, "unrecognized window seek type: %d", seektype);
-			abs_pos = 0;		/* keep compiler quiet */
-			break;
-	}
-
-	gottuple = window_gettupleslot(winobj, abs_pos, slot);
+		ignore_nulls = true;
 
-	if (!gottuple)
-	{
-		if (isout)
-			*isout = true;
-		*isnull = true;
-		return (Datum) 0;
+		if (seektype == WINDOW_SEEK_HEAD)
+		{
+			step = 1;
+			relpos = 0;
+		}
+		else if (seektype == WINDOW_SEEK_TAIL)
+		{
+			step = -1;
+			relpos = 0;
+		}
+		else
+		{
+			if (target > 0)
+				step = 1;
+			else if (target < 0)
+				step = -1;
+			else
+				step = 0;
+			relpos = step;
+		}
 	}
-	else
+
+	for (;;)
 	{
-		if (isout)
-			*isout = false;
-		if (set_mark)
-			WinSetMarkPosition(winobj, abs_pos);
+		switch (seektype)
+		{
+			case WINDOW_SEEK_CURRENT:
+				abs_pos = winstate->currentpos + relpos;
+				break;
+			case WINDOW_SEEK_HEAD:
+				abs_pos = relpos;
+				break;
+			case WINDOW_SEEK_TAIL:
+				spool_tuples(winstate, -1);
+				abs_pos = winstate->spooled_rows - 1 + relpos;
+				break;
+			default:
+				elog(ERROR, "unrecognized window seek type: %d", seektype);
+				abs_pos = 0;		/* keep compiler quiet */
+				break;
+		}
+
+		gottuple = window_gettupleslot(winobj, abs_pos, slot);
+
+		/* Did we fall off the end of the partition? */
+		if (!gottuple)
+		{
+			if (isout)
+				*isout = true;
+			*isnull = true;
+			return (Datum) 0;
+		}
+
+		/* Evaluate the expression at this row */
 		econtext->ecxt_outertuple = slot;
-		return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
-							econtext, isnull);
+		result = ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
+							  econtext, isnull);
+
+		/* If we got a null and we're ignoring them, move the goalposts */
+		if (ignore_nulls && *isnull)
+			target += step;
+
+		/* Once we've reached our target, we're done */
+		if (relpos == target)
+		{
+			if (isout)
+				*isout = false;
+			/*
+			 * We can only mark the row if we're not ignoring nulls (because we
+			 * jump straight there).
+			 */
+			if (set_mark && !ignore_nulls)
+				WinSetMarkPosition(winobj, abs_pos);
+			return result;
+		}
+
+		/* Otherwise move closer and try again */
+		relpos += step;
 	}
 }
 
@@ -3261,170 +3318,218 @@ WinGetFuncArgInFrame(WindowObject winobj, int argno,
 	TupleTableSlot *slot;
 	int64		abs_pos;
 	int64		mark_pos;
+	bool		ignore_nulls = false;
+	int			target = relpos;
+	int			step;
+	Datum		result;
 
 	Assert(WindowObjectIsValid(winobj));
 	winstate = winobj->winstate;
 	econtext = winstate->ss.ps.ps_ExprContext;
 	slot = winstate->temp_slot_1;
 
-	switch (seektype)
+	/*
+	 * If we're not ignoring nulls, we'll just go straight to the desired row.
+	 * But if we are ignoring nulls, we'll have to step towards the target row
+	 * by row so we need to determine how we get there.
+	 */
+	if (winobj->null_treatment == NULL_TREATMENT_IGNORE)
 	{
-		case WINDOW_SEEK_CURRENT:
-			elog(ERROR, "WINDOW_SEEK_CURRENT is not supported for WinGetFuncArgInFrame");
-			abs_pos = mark_pos = 0; /* keep compiler quiet */
-			break;
-		case WINDOW_SEEK_HEAD:
-			/* rejecting relpos < 0 is easy and simplifies code below */
-			if (relpos < 0)
-				goto out_of_frame;
-			update_frameheadpos(winstate);
-			abs_pos = winstate->frameheadpos + relpos;
-			mark_pos = abs_pos;
+		ignore_nulls = true;
 
-			/*
-			 * Account for exclusion option if one is active, but advance only
-			 * abs_pos not mark_pos.  This prevents changes of the current
-			 * row's peer group from resulting in trying to fetch a row before
-			 * some previous mark position.
-			 *
-			 * Note that in some corner cases such as current row being
-			 * outside frame, these calculations are theoretically too simple,
-			 * but it doesn't matter because we'll end up deciding the row is
-			 * out of frame.  We do not attempt to avoid fetching rows past
-			 * end of frame; that would happen in some cases anyway.
-			 */
-			switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
-			{
-				case 0:
-					/* no adjustment needed */
-					break;
-				case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
-					if (abs_pos >= winstate->currentpos &&
-						winstate->currentpos >= winstate->frameheadpos)
-						abs_pos++;
-					break;
-				case FRAMEOPTION_EXCLUDE_GROUP:
-					update_grouptailpos(winstate);
-					if (abs_pos >= winstate->groupheadpos &&
-						winstate->grouptailpos > winstate->frameheadpos)
-					{
-						int64		overlapstart = Max(winstate->groupheadpos,
-													   winstate->frameheadpos);
+		if (target > 0)
+			step = 1;
+		else if (target < 0)
+			step = -1;
+		else if (seektype == WINDOW_SEEK_HEAD)
+			step = 1;
+		else if (seektype == WINDOW_SEEK_TAIL)
+			step = -1;
+		else
+			step = 0;
+
+		relpos = 0;
+	}
 
-						abs_pos += winstate->grouptailpos - overlapstart;
-					}
-					break;
-				case FRAMEOPTION_EXCLUDE_TIES:
-					update_grouptailpos(winstate);
-					if (abs_pos >= winstate->groupheadpos &&
-						winstate->grouptailpos > winstate->frameheadpos)
-					{
-						int64		overlapstart = Max(winstate->groupheadpos,
-													   winstate->frameheadpos);
+	for (;;)
+	{
+		switch (seektype)
+		{
+			case WINDOW_SEEK_CURRENT:
+				elog(ERROR, "WINDOW_SEEK_CURRENT is not supported for WinGetFuncArgInFrame");
+				abs_pos = mark_pos = 0; /* keep compiler quiet */
+				break;
+			case WINDOW_SEEK_HEAD:
+				/* rejecting relpos < 0 is easy and simplifies code below */
+				if (relpos < 0)
+					goto out_of_frame;
+				update_frameheadpos(winstate);
+				abs_pos = winstate->frameheadpos + relpos;
+				mark_pos = abs_pos;
 
-						if (abs_pos == overlapstart)
-							abs_pos = winstate->currentpos;
-						else
-							abs_pos += winstate->grouptailpos - overlapstart - 1;
-					}
-					break;
-				default:
-					elog(ERROR, "unrecognized frame option state: 0x%x",
-						 winstate->frameOptions);
-					break;
-			}
-			break;
-		case WINDOW_SEEK_TAIL:
-			/* rejecting relpos > 0 is easy and simplifies code below */
-			if (relpos > 0)
-				goto out_of_frame;
-			update_frametailpos(winstate);
-			abs_pos = winstate->frametailpos - 1 + relpos;
+				/*
+				 * Account for exclusion option if one is active, but advance only
+				 * abs_pos not mark_pos.  This prevents changes of the current
+				 * row's peer group from resulting in trying to fetch a row before
+				 * some previous mark position.
+				 *
+				 * Note that in some corner cases such as current row being
+				 * outside frame, these calculations are theoretically too simple,
+				 * but it doesn't matter because we'll end up deciding the row is
+				 * out of frame.  We do not attempt to avoid fetching rows past
+				 * end of frame; that would happen in some cases anyway.
+				 */
+				switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
+				{
+					case 0:
+						/* no adjustment needed */
+						break;
+					case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
+						if (abs_pos >= winstate->currentpos &&
+							winstate->currentpos >= winstate->frameheadpos)
+							abs_pos++;
+						break;
+					case FRAMEOPTION_EXCLUDE_GROUP:
+						update_grouptailpos(winstate);
+						if (abs_pos >= winstate->groupheadpos &&
+							winstate->grouptailpos > winstate->frameheadpos)
+						{
+							int64		overlapstart = Max(winstate->groupheadpos,
+														   winstate->frameheadpos);
 
-			/*
-			 * Account for exclusion option if one is active.  If there is no
-			 * exclusion, we can safely set the mark at the accessed row.  But
-			 * if there is, we can only mark the frame start, because we can't
-			 * be sure how far back in the frame the exclusion might cause us
-			 * to fetch in future.  Furthermore, we have to actually check
-			 * against frameheadpos here, since it's unsafe to try to fetch a
-			 * row before frame start if the mark might be there already.
-			 */
-			switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
-			{
-				case 0:
-					/* no adjustment needed */
-					mark_pos = abs_pos;
-					break;
-				case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
-					if (abs_pos <= winstate->currentpos &&
-						winstate->currentpos < winstate->frametailpos)
-						abs_pos--;
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				case FRAMEOPTION_EXCLUDE_GROUP:
-					update_grouptailpos(winstate);
-					if (abs_pos < winstate->grouptailpos &&
-						winstate->groupheadpos < winstate->frametailpos)
-					{
-						int64		overlapend = Min(winstate->grouptailpos,
-													 winstate->frametailpos);
+							abs_pos += winstate->grouptailpos - overlapstart;
+						}
+						break;
+					case FRAMEOPTION_EXCLUDE_TIES:
+						update_grouptailpos(winstate);
+						if (abs_pos >= winstate->groupheadpos &&
+							winstate->grouptailpos > winstate->frameheadpos)
+						{
+							int64		overlapstart = Max(winstate->groupheadpos,
+														   winstate->frameheadpos);
 
-						abs_pos -= overlapend - winstate->groupheadpos;
-					}
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				case FRAMEOPTION_EXCLUDE_TIES:
-					update_grouptailpos(winstate);
-					if (abs_pos < winstate->grouptailpos &&
-						winstate->groupheadpos < winstate->frametailpos)
-					{
-						int64		overlapend = Min(winstate->grouptailpos,
-													 winstate->frametailpos);
+							if (abs_pos == overlapstart)
+								abs_pos = winstate->currentpos;
+							else
+								abs_pos += winstate->grouptailpos - overlapstart - 1;
+						}
+						break;
+					default:
+						elog(ERROR, "unrecognized frame option state: 0x%x",
+							 winstate->frameOptions);
+						break;
+				}
+				break;
+			case WINDOW_SEEK_TAIL:
+				/* rejecting relpos > 0 is easy and simplifies code below */
+				if (relpos > 0)
+					goto out_of_frame;
+				update_frametailpos(winstate);
+				abs_pos = winstate->frametailpos - 1 + relpos;
 
-						if (abs_pos == overlapend - 1)
-							abs_pos = winstate->currentpos;
-						else
-							abs_pos -= overlapend - 1 - winstate->groupheadpos;
-					}
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				default:
-					elog(ERROR, "unrecognized frame option state: 0x%x",
-						 winstate->frameOptions);
-					mark_pos = 0;	/* keep compiler quiet */
-					break;
-			}
-			break;
-		default:
-			elog(ERROR, "unrecognized window seek type: %d", seektype);
-			abs_pos = mark_pos = 0; /* keep compiler quiet */
-			break;
-	}
+				/*
+				 * Account for exclusion option if one is active.  If there is no
+				 * exclusion, we can safely set the mark at the accessed row.  But
+				 * if there is, we can only mark the frame start, because we can't
+				 * be sure how far back in the frame the exclusion might cause us
+				 * to fetch in future.  Furthermore, we have to actually check
+				 * against frameheadpos here, since it's unsafe to try to fetch a
+				 * row before frame start if the mark might be there already.
+				 */
+				switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
+				{
+					case 0:
+						/* no adjustment needed */
+						mark_pos = abs_pos;
+						break;
+					case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
+						if (abs_pos <= winstate->currentpos &&
+							winstate->currentpos < winstate->frametailpos)
+							abs_pos--;
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					case FRAMEOPTION_EXCLUDE_GROUP:
+						update_grouptailpos(winstate);
+						if (abs_pos < winstate->grouptailpos &&
+							winstate->groupheadpos < winstate->frametailpos)
+						{
+							int64		overlapend = Min(winstate->grouptailpos,
+														 winstate->frametailpos);
 
-	if (!window_gettupleslot(winobj, abs_pos, slot))
-		goto out_of_frame;
+							abs_pos -= overlapend - winstate->groupheadpos;
+						}
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					case FRAMEOPTION_EXCLUDE_TIES:
+						update_grouptailpos(winstate);
+						if (abs_pos < winstate->grouptailpos &&
+							winstate->groupheadpos < winstate->frametailpos)
+						{
+							int64		overlapend = Min(winstate->grouptailpos,
+														 winstate->frametailpos);
 
-	/* The code above does not detect all out-of-frame cases, so check */
-	if (row_is_in_frame(winstate, abs_pos, slot) <= 0)
-		goto out_of_frame;
+							if (abs_pos == overlapend - 1)
+								abs_pos = winstate->currentpos;
+							else
+								abs_pos -= overlapend - 1 - winstate->groupheadpos;
+						}
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					default:
+						elog(ERROR, "unrecognized frame option state: 0x%x",
+							 winstate->frameOptions);
+						mark_pos = 0;	/* keep compiler quiet */
+						break;
+				}
+				break;
+			default:
+				elog(ERROR, "unrecognized window seek type: %d", seektype);
+				abs_pos = mark_pos = 0; /* keep compiler quiet */
+				break;
+		}
 
-	if (isout)
-		*isout = false;
-	if (set_mark)
-		WinSetMarkPosition(winobj, mark_pos);
-	econtext->ecxt_outertuple = slot;
-	return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
-						econtext, isnull);
+		if (!window_gettupleslot(winobj, abs_pos, slot))
+			goto out_of_frame;
+
+		/* The code above does not detect all out-of-frame cases, so check */
+		if (row_is_in_frame(winstate, abs_pos, slot) <= 0)
+			goto out_of_frame;
+
+		/* Evaluate the expression at this row */
+		econtext->ecxt_outertuple = slot;
+		result = ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
+							  econtext, isnull);
+
+		/* If we got a null and we're ignoring them, move the goalposts */
+		if (ignore_nulls && *isnull)
+			target += step;
+
+		/* Once we've reached our target, we're done */
+		if (relpos == target)
+		{
+			if (isout)
+				*isout = false;
+			/*
+			 * We can only mark the row if we're not ignoring nulls (because we
+			 * jump straight there).
+			 */
+			if (set_mark && !ignore_nulls)
+				WinSetMarkPosition(winobj, mark_pos);
+			return result;
+		}
+
+		/* Otherwise move closer and try again */
+		relpos += step;
+	}
 
 out_of_frame:
 	if (isout)
diff --git src/backend/nodes/copyfuncs.c src/backend/nodes/copyfuncs.c
index 70f8b718e0..eba1f3f4d2 100644
--- src/backend/nodes/copyfuncs.c
+++ src/backend/nodes/copyfuncs.c
@@ -1533,6 +1533,7 @@ _copyWindowFunc(const WindowFunc *from)
 	COPY_SCALAR_FIELD(winref);
 	COPY_SCALAR_FIELD(winstar);
 	COPY_SCALAR_FIELD(winagg);
+	COPY_SCALAR_FIELD(winnulltreatment);
 	COPY_LOCATION_FIELD(location);
 
 	return newnode;
@@ -2691,6 +2692,7 @@ _copyFuncCall(const FuncCall *from)
 	COPY_SCALAR_FIELD(agg_distinct);
 	COPY_SCALAR_FIELD(func_variadic);
 	COPY_SCALAR_FIELD(funcformat);
+	COPY_SCALAR_FIELD(win_null_treatment);
 	COPY_LOCATION_FIELD(location);
 
 	return newnode;
diff --git src/backend/nodes/equalfuncs.c src/backend/nodes/equalfuncs.c
index 541e0e6b48..effed2f811 100644
--- src/backend/nodes/equalfuncs.c
+++ src/backend/nodes/equalfuncs.c
@@ -266,6 +266,7 @@ _equalWindowFunc(const WindowFunc *a, const WindowFunc *b)
 	COMPARE_SCALAR_FIELD(winref);
 	COMPARE_SCALAR_FIELD(winstar);
 	COMPARE_SCALAR_FIELD(winagg);
+	COMPARE_SCALAR_FIELD(winnulltreatment);
 	COMPARE_LOCATION_FIELD(location);
 
 	return true;
@@ -2380,6 +2381,7 @@ _equalFuncCall(const FuncCall *a, const FuncCall *b)
 	COMPARE_SCALAR_FIELD(agg_distinct);
 	COMPARE_SCALAR_FIELD(func_variadic);
 	COMPARE_SCALAR_FIELD(funcformat);
+	COMPARE_SCALAR_FIELD(win_null_treatment);
 	COMPARE_LOCATION_FIELD(location);
 
 	return true;
diff --git src/backend/nodes/makefuncs.c src/backend/nodes/makefuncs.c
index ee033ae779..587cd43e6b 100644
--- src/backend/nodes/makefuncs.c
+++ src/backend/nodes/makefuncs.c
@@ -596,6 +596,7 @@ makeFuncCall(List *name, List *args, CoercionForm funcformat, int location)
 	n->agg_distinct = false;
 	n->func_variadic = false;
 	n->funcformat = funcformat;
+	n->win_null_treatment = NULL_TREATMENT_NONE;
 	n->location = location;
 	return n;
 }
diff --git src/backend/nodes/outfuncs.c src/backend/nodes/outfuncs.c
index d78b16ed1d..164751a357 100644
--- src/backend/nodes/outfuncs.c
+++ src/backend/nodes/outfuncs.c
@@ -1184,6 +1184,7 @@ _outWindowFunc(StringInfo str, const WindowFunc *node)
 	WRITE_UINT_FIELD(winref);
 	WRITE_BOOL_FIELD(winstar);
 	WRITE_BOOL_FIELD(winagg);
+	WRITE_INT_FIELD(winnulltreatment);
 	WRITE_LOCATION_FIELD(location);
 }
 
@@ -2790,6 +2791,7 @@ _outFuncCall(StringInfo str, const FuncCall *node)
 	WRITE_BOOL_FIELD(agg_distinct);
 	WRITE_BOOL_FIELD(func_variadic);
 	WRITE_ENUM_FIELD(funcformat, CoercionForm);
+	WRITE_BOOL_FIELD(win_null_treatment);
 	WRITE_LOCATION_FIELD(location);
 }
 
diff --git src/backend/nodes/readfuncs.c src/backend/nodes/readfuncs.c
index 0f6a77afc4..587757f2c9 100644
--- src/backend/nodes/readfuncs.c
+++ src/backend/nodes/readfuncs.c
@@ -656,6 +656,7 @@ _readWindowFunc(void)
 	READ_UINT_FIELD(winref);
 	READ_BOOL_FIELD(winstar);
 	READ_BOOL_FIELD(winagg);
+	READ_INT_FIELD(winnulltreatment);
 	READ_LOCATION_FIELD(location);
 
 	READ_DONE();
diff --git src/backend/optimizer/util/clauses.c src/backend/optimizer/util/clauses.c
index 8f5cbf99f4..85ea709d81 100644
--- src/backend/optimizer/util/clauses.c
+++ src/backend/optimizer/util/clauses.c
@@ -2221,6 +2221,7 @@ eval_const_expressions_mutator(Node *node,
 				newexpr->winref = expr->winref;
 				newexpr->winstar = expr->winstar;
 				newexpr->winagg = expr->winagg;
+				newexpr->winnulltreatment = expr->winnulltreatment;
 				newexpr->location = expr->location;
 
 				return (Node *) newexpr;
diff --git src/backend/parser/gram.y src/backend/parser/gram.y
index 8f341ac006..59d72207c9 100644
--- src/backend/parser/gram.y
+++ src/backend/parser/gram.y
@@ -582,6 +582,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <list>	window_clause window_definition_list opt_partition_clause
 %type <windef>	window_definition over_clause window_specification
 				opt_frame_clause frame_extent frame_bound
+%type <ival>	null_treatment
 %type <ival>	opt_window_exclusion_clause
 %type <str>		opt_existing_window_name
 %type <boolean> opt_if_not_exists
@@ -650,7 +651,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 	HANDLER HAVING HEADER_P HOLD HOUR_P
 
-	IDENTITY_P IF_P ILIKE IMMEDIATE IMMUTABLE IMPLICIT_P IMPORT_P IN_P INCLUDE
+	IDENTITY_P IF_P IGNORE_P ILIKE IMMEDIATE IMMUTABLE IMPLICIT_P IMPORT_P IN_P INCLUDE
 	INCLUDING INCREMENT INDEX INDEXES INHERIT INHERITS INITIALLY INLINE_P
 	INNER_P INOUT INPUT_P INSENSITIVE INSERT INSTEAD INT_P INTEGER
 	INTERSECT INTERVAL INTO INVOKER IS ISNULL ISOLATION
@@ -682,7 +683,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 	RANGE READ REAL REASSIGN RECHECK RECURSIVE REF REFERENCES REFERENCING
 	REFRESH REINDEX RELATIVE_P RELEASE RENAME REPEATABLE REPLACE REPLICA
-	RESET RESTART RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROLLUP
+	RESET RESPECT RESTART RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROLLUP
 	ROUTINE ROUTINES ROW ROWS RULE
 
 	SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
@@ -7799,6 +7800,10 @@ createfunc_opt_item:
 				{
 					$$ = makeDefElem("window", (Node *)makeInteger(true), @1);
 				}
+			| TREAT NULLS_P
+				{
+					$$ = makeDefElem("null_treatment", (Node *)makeInteger(true), @1);
+				}
 			| common_func_opt_item
 				{
 					$$ = $1;
@@ -13676,6 +13681,14 @@ func_expr: func_application within_group_clause filter_clause over_clause
 					}
 					n->agg_filter = $3;
 					n->over = $4;
+					n->win_null_treatment = NULL_TREATMENT_NONE;
+					$$ = (Node *) n;
+				}
+			| func_application null_treatment over_clause
+				{
+					FuncCall *n = (FuncCall *) $1;
+					n->over = $3;
+					n->win_null_treatment = $2;
 					$$ = (Node *) n;
 				}
 			| func_expr_common_subexpr
@@ -14096,6 +14109,11 @@ window_definition:
 				}
 		;
 
+null_treatment:
+			IGNORE_P NULLS_P	{ $$ = NULL_TREATMENT_IGNORE; }
+			| RESPECT NULLS_P	{ $$ = NULL_TREATMENT_RESPECT; }
+		;
+
 over_clause: OVER window_specification
 				{ $$ = $2; }
 			| OVER ColId
@@ -15177,6 +15195,7 @@ unreserved_keyword:
 			| HOUR_P
 			| IDENTITY_P
 			| IF_P
+			| IGNORE_P
 			| IMMEDIATE
 			| IMMUTABLE
 			| IMPLICIT_P
@@ -15283,6 +15302,7 @@ unreserved_keyword:
 			| REPLACE
 			| REPLICA
 			| RESET
+			| RESPECT
 			| RESTART
 			| RESTRICT
 			| RETURNS
diff --git src/backend/parser/parse_func.c src/backend/parser/parse_func.c
index 23ac2a2fe6..b42850f91e 100644
--- src/backend/parser/parse_func.c
+++ src/backend/parser/parse_func.c
@@ -97,6 +97,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 	bool		agg_distinct = (fn ? fn->agg_distinct : false);
 	bool		func_variadic = (fn ? fn->func_variadic : false);
 	CoercionForm funcformat = (fn ? fn->funcformat : COERCE_EXPLICIT_CALL);
+	NullTreatment	win_null_treatment = (fn ? fn->win_null_treatment : NULL_TREATMENT_NONE);
 	bool		could_be_projection;
 	Oid			rettype;
 	Oid			funcid;
@@ -108,6 +109,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 	Oid		   *declared_arg_types;
 	List	   *argnames;
 	List	   *argdefaults;
+	bool		null_treatment;
 	Node	   *retval;
 	bool		retset;
 	int			nvargs;
@@ -267,7 +269,8 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 							   !func_variadic, true,
 							   &funcid, &rettype, &retset,
 							   &nvargs, &vatype,
-							   &declared_arg_types, &argdefaults);
+							   &declared_arg_types, &argdefaults,
+							   &null_treatment);
 
 	cancel_parser_errposition_callback(&pcbstate);
 
@@ -507,6 +510,13 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 						 errmsg("%s is not an ordered-set aggregate, so it cannot have WITHIN GROUP",
 								NameListToString(funcname)),
 						 parser_errposition(pstate, location)));
+
+			/* It also can't treat nulls as a window function */
+			if (over && win_null_treatment != NULL_TREATMENT_NONE)
+				ereport(ERROR,
+						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+						 errmsg("aggregate functions do not accept RESPECT/IGNORE NULLS"),
+						 parser_errposition(pstate, location)));
 		}
 	}
 	else if (fdresult == FUNCDETAIL_WINDOWFUNC)
@@ -527,6 +537,13 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 					 errmsg("window function %s cannot have WITHIN GROUP",
 							NameListToString(funcname)),
 					 parser_errposition(pstate, location)));
+
+		if (!null_treatment && win_null_treatment != NULL_TREATMENT_NONE)
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("window function %s does not accept RESPECT/IGNORE NULLS",
+							NameListToString(funcname)),
+					 parser_errposition(pstate, location)));
 	}
 	else if (fdresult == FUNCDETAIL_COERCION)
 	{
@@ -826,6 +843,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 		wfunc->winstar = agg_star;
 		wfunc->winagg = (fdresult == FUNCDETAIL_AGGREGATE);
 		wfunc->aggfilter = agg_filter;
+		wfunc->winnulltreatment = win_null_treatment;
 		wfunc->location = location;
 
 		/*
@@ -1396,7 +1414,8 @@ func_get_detail(List *funcname,
 				int *nvargs,	/* return value */
 				Oid *vatype,	/* return value */
 				Oid **true_typeids, /* return value */
-				List **argdefaults) /* optional return value */
+				List **argdefaults, /* optional return value */
+				bool *null_treatment) /* optional return value */
 {
 	FuncCandidateList raw_candidates;
 	FuncCandidateList best_candidate;
@@ -1410,6 +1429,8 @@ func_get_detail(List *funcname,
 	*true_typeids = NULL;
 	if (argdefaults)
 		*argdefaults = NIL;
+	if (null_treatment)
+		*null_treatment = NULL_TREATMENT_NONE;
 
 	/* Get list of possible candidates from namespace search */
 	raw_candidates = FuncnameGetCandidates(funcname, nargs, fargnames,
@@ -1687,6 +1708,8 @@ func_get_detail(List *funcname,
 				*argdefaults = defaults;
 			}
 		}
+		if (null_treatment)
+			*null_treatment = pform->pronulltreatment;
 
 		switch (pform->prokind)
 		{
diff --git src/backend/utils/adt/ruleutils.c src/backend/utils/adt/ruleutils.c
index 7d4443e807..9e41b61c08 100644
--- src/backend/utils/adt/ruleutils.c
+++ src/backend/utils/adt/ruleutils.c
@@ -2660,6 +2660,9 @@ pg_get_functiondef(PG_FUNCTION_ARGS)
 
 	if (proc->prokind == PROKIND_WINDOW)
 		appendStringInfoString(&buf, " WINDOW");
+	if (proc->pronulltreatment)
+		appendStringInfoString(&buf, " TREAT NULLS");
+
 	switch (proc->provolatile)
 	{
 		case PROVOLATILE_IMMUTABLE:
@@ -9474,7 +9477,12 @@ get_windowfunc_expr(WindowFunc *wfunc, deparse_context *context)
 		get_rule_expr((Node *) wfunc->aggfilter, context, false);
 	}
 
-	appendStringInfoString(buf, ") OVER ");
+	if (wfunc->winnulltreatment == NULL_TREATMENT_IGNORE)
+		appendStringInfoString(buf, ") IGNORE NULLS OVER ");
+	else if (wfunc->winnulltreatment == NULL_TREATMENT_RESPECT)
+		appendStringInfoString(buf, ") RESPECT NULLS OVER ");
+	else
+		appendStringInfoString(buf, ") OVER ");
 
 	foreach(l, context->windowClause)
 	{
@@ -11227,7 +11235,7 @@ generate_function_name(Oid funcid, int nargs, List *argnames, Oid *argtypes,
 								   !use_variadic, true,
 								   &p_funcid, &p_rettype,
 								   &p_retset, &p_nvargs, &p_vatype,
-								   &p_true_typeids, NULL);
+								   &p_true_typeids, NULL, NULL);
 	else
 	{
 		p_result = FUNCDETAIL_NOTFOUND;
diff --git src/test/regress/expected/create_function_3.out src/test/regress/expected/create_function_3.out
index ce508ae1dc..0311f8ecc9 100644
--- src/test/regress/expected/create_function_3.out
+++ src/test/regress/expected/create_function_3.out
@@ -122,6 +122,12 @@ SELECT proname, prosecdef FROM pg_proc
  functest_c_3 | t
 (3 rows)
 
+--
+-- TREAT NULLS
+--
+CREATE FUNCTION functest_D_1(integer) RETURNS integer LANGUAGE 'sql'
+       TREAT NULLS AS 'SELECT $1';
+ERROR:  cannot set null treatment on a non-window function
 --
 -- LEAKPROOF
 --
@@ -298,6 +304,8 @@ CREATE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL AS 'SELECT $1';
 CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL WINDOW AS 'SELECT $1';
 ERROR:  cannot change routine kind
 DETAIL:  "functest1" is a function.
+CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL TREAT NULLS AS 'SELECT $1';
+ERROR:  cannot set null treatment on a non-window function
 CREATE OR REPLACE PROCEDURE functest1(a int) LANGUAGE SQL AS 'SELECT $1';
 ERROR:  cannot change routine kind
 DETAIL:  "functest1" is a function.
diff --git src/test/regress/expected/create_procedure.out src/test/regress/expected/create_procedure.out
index 3838fa2324..f81f9b79cc 100644
--- src/test/regress/expected/create_procedure.out
+++ src/test/regress/expected/create_procedure.out
@@ -174,6 +174,10 @@ CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT INTO cp_test VALUES (
 ERROR:  invalid attribute in procedure definition
 LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT I...
                                                ^
+CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
+ERROR:  invalid attribute in procedure definition
+LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INS...
+                                               ^
 CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 ERROR:  invalid attribute in procedure definition
 LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT I...
diff --git src/test/regress/expected/misc_sanity.out src/test/regress/expected/misc_sanity.out
index d40afeef78..8615d78075 100644
--- src/test/regress/expected/misc_sanity.out
+++ src/test/regress/expected/misc_sanity.out
@@ -109,3 +109,13 @@ ORDER BY 1, 2;
  pg_largeobject_metadata | lomacl        | aclitem[]
 (11 rows)
 
+-- **************** pg_class ****************
+-- Look for non-window functions with null treatment (there should be none)
+SELECT proname, prokind, pronulltreatment
+FROM pg_proc
+WHERE pronulltreatment AND prokind <> 'w'
+ORDER BY oid;
+ proname | prokind | pronulltreatment 
+---------+---------+------------------
+(0 rows)
+
diff --git src/test/regress/expected/window.out src/test/regress/expected/window.out
index 19e2ac518a..3bd9584c6c 100644
--- src/test/regress/expected/window.out
+++ src/test/regress/expected/window.out
@@ -4063,3 +4063,214 @@ SELECT * FROM pg_temp.f(2);
  {5}
 (5 rows)
 
+-- IGNORE NULLS tests
+CREATE TEMPORARY TABLE planets (
+    name text,
+    orbit integer
+);
+INSERT INTO planets VALUES
+  ('mercury', 88),
+  ('venus', 224),
+  ('earth', NULL),
+  ('mars', NULL),
+  ('jupiter', 4332),
+  ('saturn', 24491),
+  ('uranus', NULL),
+  ('neptune', 60182),
+  ('pluto', 90560),
+  ('xyzzy', NULL);
+-- test ruleutils
+CREATE VIEW planets_view AS
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+NOTICE:  view "planets_view" will be a temporary view
+SELECT pg_get_viewdef('planets_view');
+                       pg_get_viewdef                        
+-------------------------------------------------------------
+  SELECT planets.name,                                      +
+     planets.orbit,                                         +
+     lag(planets.orbit) OVER w AS lag,                      +
+     lag(planets.orbit) RESPECT NULLS OVER w AS lag_respect,+
+     lag(planets.orbit) IGNORE NULLS OVER w AS lag_ignore   +
+    FROM planets                                            +
+   WINDOW w AS (ORDER BY planets.name);
+(1 row)
+
+-- lag
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+  name   | orbit |  lag  | lag_respect | lag_ignore 
+---------+-------+-------+-------------+------------
+ earth   |       |       |             |           
+ jupiter |  4332 |       |             |           
+ mars    |       |  4332 |        4332 |       4332
+ mercury |    88 |       |             |       4332
+ neptune | 60182 |    88 |          88 |         88
+ pluto   | 90560 | 60182 |       60182 |      60182
+ saturn  | 24491 | 90560 |       90560 |      90560
+ uranus  |       | 24491 |       24491 |      24491
+ venus   |   224 |       |             |      24491
+ xyzzy   |       |   224 |         224 |        224
+(10 rows)
+
+-- lead
+SELECT name,
+       orbit,
+       lead(orbit) OVER w AS lead,
+       lead(orbit) RESPECT NULLS OVER w AS lead_respect,
+       lead(orbit) IGNORE NULLS OVER w AS lead_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+  name   | orbit | lead  | lead_respect | lead_ignore 
+---------+-------+-------+--------------+-------------
+ earth   |       |  4332 |         4332 |        4332
+ jupiter |  4332 |       |              |          88
+ mars    |       |    88 |           88 |          88
+ mercury |    88 | 60182 |        60182 |       60182
+ neptune | 60182 | 90560 |        90560 |       90560
+ pluto   | 90560 | 24491 |        24491 |       24491
+ saturn  | 24491 |       |              |         224
+ uranus  |       |   224 |          224 |         224
+ venus   |   224 |       |              |            
+ xyzzy   |       |       |              |            
+(10 rows)
+
+-- first_value
+SELECT name,
+       orbit,
+       first_value(orbit) RESPECT NULLS OVER w1,
+       first_value(orbit) IGNORE NULLS OVER w1,
+       first_value(orbit) RESPECT NULLS OVER w2,
+       first_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | first_value | first_value | first_value | first_value 
+---------+-------+-------------+-------------+-------------+-------------
+ earth   |       |             |        4332 |             |        4332
+ jupiter |  4332 |             |        4332 |             |        4332
+ mars    |       |             |        4332 |             |        4332
+ mercury |    88 |             |        4332 |        4332 |        4332
+ neptune | 60182 |             |        4332 |             |          88
+ pluto   | 90560 |             |        4332 |          88 |          88
+ saturn  | 24491 |             |        4332 |       60182 |       60182
+ uranus  |       |             |        4332 |       90560 |       90560
+ venus   |   224 |             |        4332 |       24491 |       24491
+ xyzzy   |       |             |        4332 |             |         224
+(10 rows)
+
+-- nth_value
+SELECT name,
+       orbit,
+       nth_value(orbit, 2) RESPECT NULLS OVER w1,
+       nth_value(orbit, 2) IGNORE NULLS OVER w1,
+       nth_value(orbit, 2) RESPECT NULLS OVER w2,
+       nth_value(orbit, 2) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | nth_value | nth_value | nth_value | nth_value 
+---------+-------+-----------+-----------+-----------+-----------
+ earth   |       |      4332 |        88 |      4332 |          
+ jupiter |  4332 |      4332 |        88 |      4332 |        88
+ mars    |       |      4332 |        88 |      4332 |        88
+ mercury |    88 |      4332 |        88 |           |        88
+ neptune | 60182 |      4332 |        88 |        88 |     60182
+ pluto   | 90560 |      4332 |        88 |     60182 |     60182
+ saturn  | 24491 |      4332 |        88 |     90560 |     90560
+ uranus  |       |      4332 |        88 |     24491 |     24491
+ venus   |   224 |      4332 |        88 |           |       224
+ xyzzy   |       |      4332 |        88 |       224 |          
+(10 rows)
+
+-- last_value
+SELECT name,
+       orbit,
+       last_value(orbit) RESPECT NULLS OVER w1,
+       last_value(orbit) IGNORE NULLS OVER w1,
+       last_value(orbit) RESPECT NULLS OVER w2,
+       last_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | last_value | last_value | last_value | last_value 
+---------+-------+------------+------------+------------+------------
+ earth   |       |            |        224 |            |       4332
+ jupiter |  4332 |            |        224 |         88 |         88
+ mars    |       |            |        224 |      60182 |      60182
+ mercury |    88 |            |        224 |      90560 |      90560
+ neptune | 60182 |            |        224 |      24491 |      24491
+ pluto   | 90560 |            |        224 |            |      24491
+ saturn  | 24491 |            |        224 |        224 |        224
+ uranus  |       |            |        224 |            |        224
+ venus   |   224 |            |        224 |            |        224
+ xyzzy   |       |            |        224 |            |        224
+(10 rows)
+
+-- window function without null treatment
+SELECT row_number() OVER (ORDER BY name) FROM planets;
+ row_number 
+------------
+          1
+          2
+          3
+          4
+          5
+          6
+          7
+          8
+          9
+         10
+(10 rows)
+
+SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM planets; -- fails
+ERROR:  window function row_number does not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM ...
+               ^
+SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM planets; -- fails
+ERROR:  window function row_number does not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM p...
+               ^
+-- regular aggregate
+SELECT sum(orbit) OVER () FROM planets;
+  sum   
+--------
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+(10 rows)
+
+SELECT sum(orbit) RESPECT NULLS OVER () FROM planets; -- fails
+ERROR:  aggregate functions do not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT sum(orbit) RESPECT NULLS OVER () FROM planets;
+               ^
+SELECT sum(orbit) IGNORE NULLS OVER () FROM planets; -- fails
+ERROR:  aggregate functions do not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT sum(orbit) IGNORE NULLS OVER () FROM planets;
+               ^
+--cleanup
+DROP TABLE planets CASCADE;
+NOTICE:  drop cascades to view planets_view
diff --git src/test/regress/sql/create_function_3.sql src/test/regress/sql/create_function_3.sql
index bd108a918f..f7fe984e58 100644
--- src/test/regress/sql/create_function_3.sql
+++ src/test/regress/sql/create_function_3.sql
@@ -82,6 +82,12 @@ SELECT proname, prosecdef FROM pg_proc
                      'functest_C_2'::regproc,
                      'functest_C_3'::regproc) ORDER BY proname;
 
+--
+-- TREAT NULLS
+--
+CREATE FUNCTION functest_D_1(integer) RETURNS integer LANGUAGE 'sql'
+       TREAT NULLS AS 'SELECT $1';
+
 --
 -- LEAKPROOF
 --
@@ -190,6 +196,7 @@ DROP FUNCTION functest_b_2;  -- error, ambiguous
 
 CREATE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL AS 'SELECT $1';
 CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL WINDOW AS 'SELECT $1';
+CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL TREAT NULLS AS 'SELECT $1';
 CREATE OR REPLACE PROCEDURE functest1(a int) LANGUAGE SQL AS 'SELECT $1';
 DROP FUNCTION functest1(a int);
 
diff --git src/test/regress/sql/create_procedure.sql src/test/regress/sql/create_procedure.sql
index 2ef1c82cea..188f5f85a9 100644
--- src/test/regress/sql/create_procedure.sql
+++ src/test/regress/sql/create_procedure.sql
@@ -130,6 +130,7 @@ CALL version();  -- error: not a procedure
 CALL sum(1);  -- error: not a procedure
 
 CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
+CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 
 ALTER PROCEDURE ptest1(text) STRICT;
diff --git src/test/regress/sql/misc_sanity.sql src/test/regress/sql/misc_sanity.sql
index 3ce32e4725..ccb4f008d9 100644
--- src/test/regress/sql/misc_sanity.sql
+++ src/test/regress/sql/misc_sanity.sql
@@ -94,3 +94,12 @@ WHERE c.oid < 16384 AND
       relkind = 'r' AND
       attstorage != 'p'
 ORDER BY 1, 2;
+
+-- **************** pg_class ****************
+
+-- Look for non-window functions with null treatment (there should be none)
+
+SELECT proname, prokind, pronulltreatment
+FROM pg_proc
+WHERE pronulltreatment AND prokind <> 'w'
+ORDER BY oid;
diff --git src/test/regress/sql/window.sql src/test/regress/sql/window.sql
index eae5fa6017..a021ed3544 100644
--- src/test/regress/sql/window.sql
+++ src/test/regress/sql/window.sql
@@ -1328,3 +1328,104 @@ $$ LANGUAGE SQL STABLE;
 
 EXPLAIN (costs off) SELECT * FROM pg_temp.f(2);
 SELECT * FROM pg_temp.f(2);
+
+
+-- IGNORE NULLS tests
+
+CREATE TEMPORARY TABLE planets (
+    name text,
+    orbit integer
+);
+
+INSERT INTO planets VALUES
+  ('mercury', 88),
+  ('venus', 224),
+  ('earth', NULL),
+  ('mars', NULL),
+  ('jupiter', 4332),
+  ('saturn', 24491),
+  ('uranus', NULL),
+  ('neptune', 60182),
+  ('pluto', 90560),
+  ('xyzzy', NULL);
+
+-- test ruleutils
+CREATE VIEW planets_view AS
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+SELECT pg_get_viewdef('planets_view');
+
+-- lag
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+
+-- lead
+SELECT name,
+       orbit,
+       lead(orbit) OVER w AS lead,
+       lead(orbit) RESPECT NULLS OVER w AS lead_respect,
+       lead(orbit) IGNORE NULLS OVER w AS lead_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+
+-- first_value
+SELECT name,
+       orbit,
+       first_value(orbit) RESPECT NULLS OVER w1,
+       first_value(orbit) IGNORE NULLS OVER w1,
+       first_value(orbit) RESPECT NULLS OVER w2,
+       first_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- nth_value
+SELECT name,
+       orbit,
+       nth_value(orbit, 2) RESPECT NULLS OVER w1,
+       nth_value(orbit, 2) IGNORE NULLS OVER w1,
+       nth_value(orbit, 2) RESPECT NULLS OVER w2,
+       nth_value(orbit, 2) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- last_value
+SELECT name,
+       orbit,
+       last_value(orbit) RESPECT NULLS OVER w1,
+       last_value(orbit) IGNORE NULLS OVER w1,
+       last_value(orbit) RESPECT NULLS OVER w2,
+       last_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- window function without null treatment
+SELECT row_number() OVER (ORDER BY name) FROM planets;
+SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM planets; -- fails
+SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM planets; -- fails
+
+-- regular aggregate
+SELECT sum(orbit) OVER () FROM planets;
+SELECT sum(orbit) RESPECT NULLS OVER () FROM planets; -- fails
+SELECT sum(orbit) IGNORE NULLS OVER () FROM planets; -- fails
+
+--cleanup
+DROP TABLE planets CASCADE;

--------------2.29.2--

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 5021ac1ca9..0e877c48df 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -20373,6 +20373,14 @@ SELECT count(*) FROM sometable;
    about frame specifications.
   </para>
 
+  <para>
+   The functions <function>lead</function>, <function>lag</function>,
+   <function>first_value</function>, <function>last_value</function>, and
+   <function>nth_value</function> accept a null treatment option which is
+   <literal>RESPECT NULLS</literal> or <literal>IGNORE NULLS</literal>.
+   If this option is not specified, the default is <literal>RESPECT NULLS</literal>.
+  </para>
+
   <para>
    When an aggregate function is used as a window function, it aggregates
    over the rows within the current row's window frame.
@@ -20386,14 +20394,9 @@ SELECT count(*) FROM sometable;
 
   <note>
    <para>
-    The SQL standard defines a <literal>RESPECT NULLS</literal> or
-    <literal>IGNORE NULLS</literal> option for <function>lead</function>, <function>lag</function>,
-    <function>first_value</function>, <function>last_value</function>, and
-    <function>nth_value</function>.  This is not implemented in
-    <productname>PostgreSQL</productname>: the behavior is always the
-    same as the standard's default, namely <literal>RESPECT NULLS</literal>.
-    Likewise, the standard's <literal>FROM FIRST</literal> or <literal>FROM LAST</literal>
-    option for <function>nth_value</function> is not implemented: only the
+    The SQL standard defines a <literal>FROM FIRST</literal> or <literal>FROM LAST</literal>
+    option for <function>nth_value</function>.  This is not implemented in
+    <productname>PostgreSQL</productname>: only the
     default <literal>FROM FIRST</literal> behavior is supported.  (You can achieve
     the result of <literal>FROM LAST</literal> by reversing the <literal>ORDER BY</literal>
     ordering.)
diff --git a/doc/src/sgml/ref/create_function.sgml b/doc/src/sgml/ref/create_function.sgml
index 3c1eaea651..31e08c26b4 100644
--- a/doc/src/sgml/ref/create_function.sgml
+++ b/doc/src/sgml/ref/create_function.sgml
@@ -28,6 +28,7 @@ CREATE [ OR REPLACE ] FUNCTION
   { LANGUAGE <replaceable class="parameter">lang_name</replaceable>
     | TRANSFORM { FOR TYPE <replaceable class="parameter">type_name</replaceable> } [, ... ]
     | WINDOW
+    | TREAT NULLS
     | IMMUTABLE | STABLE | VOLATILE | [ NOT ] LEAKPROOF
     | CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
     | [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
@@ -293,6 +294,17 @@ CREATE [ OR REPLACE ] FUNCTION
      </listitem>
     </varlistentry>
 
+    <varlistentry>
+     <term><literal>TREAT NULLS</literal></term>
+
+     <listitem>
+      <para><literal>TREAT NULLS</literal> indicates that the function is able
+      to handle the <literal>RESPECT NULLS</literal> and <literal>IGNORE
+      NULLS</literal> options.  Only window functions may specify this.
+      </para>
+     </listitem>
+    </varlistentry>
+
     <varlistentry>
      <term><literal>IMMUTABLE</literal></term>
      <term><literal>STABLE</literal></term>
diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml
index d66560b587..103595d21b 100644
--- a/doc/src/sgml/syntax.sgml
+++ b/doc/src/sgml/syntax.sgml
@@ -1766,6 +1766,8 @@ FROM generate_series(1,10) AS s(i);
     The syntax of a window function call is one of the following:
 
 <synopsis>
+<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ RESPECT NULLS | IGNORE NULLS ] OVER <replaceable>window_name</replaceable>
+<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ RESPECT NULLS | IGNORE NULLS ] OVER ( <replaceable class="parameter">window_definition</replaceable> )
 <replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER <replaceable>window_name</replaceable>
 <replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER ( <replaceable class="parameter">window_definition</replaceable> )
 <replaceable>function_name</replaceable> ( * ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER <replaceable>window_name</replaceable>
@@ -1779,6 +1781,18 @@ FROM generate_series(1,10) AS s(i);
 [ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [ NULLS { FIRST | LAST } ] [, ...] ]
 [ <replaceable class="parameter">frame_clause</replaceable> ]
 </synopsis>
+   </para>
+
+   <note>
+    <para>
+     The versions with <literal>RESPECT NULLS</literal> or <literal>IGNORE
+     NULLS</literal> only apply to true window functions, whereas the versions
+     with <literal>FILTER</literal> only apply to aggregate functions used as
+     window functions.
+    </para>
+   </note>
+
+   <para>
     The optional <replaceable class="parameter">frame_clause</replaceable>
     can be one of
 <synopsis>
diff --git a/src/backend/catalog/pg_aggregate.c b/src/backend/catalog/pg_aggregate.c
index 7664bb6285..fea8778ec8 100644
--- a/src/backend/catalog/pg_aggregate.c
+++ b/src/backend/catalog/pg_aggregate.c
@@ -627,6 +627,7 @@ AggregateCreate(const char *aggName,
 									 * definable for agg) */
 							 false, /* isLeakProof */
 							 false, /* isStrict (not needed for agg) */
+							 false, /* null_treatment (not needed for agg) */
 							 PROVOLATILE_IMMUTABLE, /* volatility (not needed
 													 * for agg) */
 							 proparallel,
@@ -848,7 +849,7 @@ lookup_agg_function(List *fnName,
 							   nargs, input_types, false, false,
 							   &fnOid, rettype, &retset,
 							   &nvargs, &vatype,
-							   &true_oid_array, NULL);
+							   &true_oid_array, NULL, NULL);
 
 	/* only valid case is a normal function not returning a set */
 	if (fdresult != FUNCDETAIL_NORMAL || !OidIsValid(fnOid))
diff --git a/src/backend/catalog/pg_proc.c b/src/backend/catalog/pg_proc.c
index 1dd9ecc063..2783b0d630 100644
--- a/src/backend/catalog/pg_proc.c
+++ b/src/backend/catalog/pg_proc.c
@@ -80,6 +80,7 @@ ProcedureCreate(const char *procedureName,
 				bool security_definer,
 				bool isLeakProof,
 				bool isStrict,
+				bool null_treatment,
 				char volatility,
 				char parallel,
 				oidvector *parameterTypes,
@@ -307,6 +308,7 @@ ProcedureCreate(const char *procedureName,
 	values[Anum_pg_proc_prosecdef - 1] = BoolGetDatum(security_definer);
 	values[Anum_pg_proc_proleakproof - 1] = BoolGetDatum(isLeakProof);
 	values[Anum_pg_proc_proisstrict - 1] = BoolGetDatum(isStrict);
+	values[Anum_pg_proc_pronulltreatment - 1] = BoolGetDatum(null_treatment);
 	values[Anum_pg_proc_proretset - 1] = BoolGetDatum(returnsSet);
 	values[Anum_pg_proc_provolatile - 1] = CharGetDatum(volatility);
 	values[Anum_pg_proc_proparallel - 1] = CharGetDatum(parallel);
@@ -386,6 +388,12 @@ ProcedureCreate(const char *procedureName,
 					  errdetail("\"%s\" is a window function.", procedureName) :
 					  0)));
 
+		/* Not okay to set null treatment if not a window function */
+		if (null_treatment && oldproc->prokind != PROKIND_WINDOW)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+					 errmsg("cannot set null treatment on a non-window function")));
+
 		dropcmd = (prokind == PROKIND_PROCEDURE ? "DROP PROCEDURE" :
 				   prokind == PROKIND_AGGREGATE ? "DROP AGGREGATE" :
 				   "DROP FUNCTION");
diff --git a/src/backend/catalog/sql_features.txt b/src/backend/catalog/sql_features.txt
index caa971c435..0615b08858 100644
--- a/src/backend/catalog/sql_features.txt
+++ b/src/backend/catalog/sql_features.txt
@@ -508,9 +508,9 @@ T612	Advanced OLAP operations			YES
 T613	Sampling			YES	
 T614	NTILE function			YES	
 T615	LEAD and LAG functions			YES	
-T616	Null treatment option for LEAD and LAG functions			NO	
+T616	Null treatment option for LEAD and LAG functions			YES	
 T617	FIRST_VALUE and LAST_VALUE function			YES	
-T618	NTH_VALUE function			NO	function exists, but some options missing
+T618	NTH_VALUE function			NO	supported except FROM LAST is not implemented
 T619	Nested window functions			NO	
 T620	WINDOW clause: GROUPS option			YES	
 T621	Enhanced numeric functions			YES	
diff --git a/src/backend/commands/functioncmds.c b/src/backend/commands/functioncmds.c
index c3ce480c8f..245a768463 100644
--- a/src/backend/commands/functioncmds.c
+++ b/src/backend/commands/functioncmds.c
@@ -697,6 +697,7 @@ compute_function_attributes(ParseState *pstate,
 							bool *windowfunc_p,
 							char *volatility_p,
 							bool *strict_p,
+							bool *null_treatment_p,
 							bool *security_definer,
 							bool *leakproof_p,
 							ArrayType **proconfig,
@@ -710,6 +711,7 @@ compute_function_attributes(ParseState *pstate,
 	DefElem    *language_item = NULL;
 	DefElem    *transform_item = NULL;
 	DefElem    *windowfunc_item = NULL;
+	DefElem    *nulltreatment_item = NULL;
 	DefElem    *volatility_item = NULL;
 	DefElem    *strict_item = NULL;
 	DefElem    *security_item = NULL;
@@ -765,6 +767,20 @@ compute_function_attributes(ParseState *pstate,
 						 parser_errposition(pstate, defel->location)));
 			windowfunc_item = defel;
 		}
+		else if (strcmp(defel->defname, "null_treatment") == 0)
+		{
+			if (nulltreatment_item)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 parser_errposition(pstate, defel->location)));
+			if (is_procedure)
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+						 errmsg("invalid attribute in procedure definition"),
+						 parser_errposition(pstate, defel->location)));
+			nulltreatment_item = defel;
+		}
 		else if (compute_common_attribute(pstate,
 										  is_procedure,
 										  defel,
@@ -816,6 +832,14 @@ compute_function_attributes(ParseState *pstate,
 		*volatility_p = interpret_func_volatility(volatility_item);
 	if (strict_item)
 		*strict_p = intVal(strict_item->arg);
+	if (nulltreatment_item)
+	{
+		*null_treatment_p = intVal(nulltreatment_item->arg);
+		if (*null_treatment_p && !*windowfunc_p)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+					 errmsg("cannot set null treatment on a non-window function")));
+	}
 	if (security_item)
 		*security_definer = intVal(security_item->arg);
 	if (leakproof_item)
@@ -941,6 +965,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 				isStrict,
 				security,
 				isLeakProof;
+	bool		null_treatment;
 	char		volatility;
 	ArrayType  *proconfig;
 	float4		procost;
@@ -964,6 +989,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 	/* Set default attributes */
 	isWindowFunc = false;
 	isStrict = false;
+	null_treatment = false;
 	security = false;
 	isLeakProof = false;
 	volatility = PROVOLATILE_VOLATILE;
@@ -979,7 +1005,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 								stmt->options,
 								&as_clause, &language, &transformDefElem,
 								&isWindowFunc, &volatility,
-								&isStrict, &security, &isLeakProof,
+								&isStrict, &null_treatment, &security, &isLeakProof,
 								&proconfig, &procost, &prorows,
 								&prosupport, &parallel);
 
@@ -1159,6 +1185,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 						   security,
 						   isLeakProof,
 						   isStrict,
+						   null_treatment,
 						   volatility,
 						   parallel,
 						   parameterTypes,
diff --git a/src/backend/commands/typecmds.c b/src/backend/commands/typecmds.c
index a0a8695b1b..15eb9e9339 100644
--- a/src/backend/commands/typecmds.c
+++ b/src/backend/commands/typecmds.c
@@ -1779,6 +1779,7 @@ makeRangeConstructors(const char *name, Oid namespace,
 								 false, /* security_definer */
 								 false, /* leakproof */
 								 false, /* isStrict */
+								 false, /* null_treatment */
 								 PROVOLATILE_IMMUTABLE, /* volatility */
 								 PROPARALLEL_SAFE,	/* parallel safety */
 								 constructorArgTypesVector, /* parameterTypes */
@@ -1843,6 +1844,7 @@ makeMultirangeConstructors(const char *name, Oid namespace,
 							 false, /* security_definer */
 							 false, /* leakproof */
 							 false, /* isStrict */
+							 false, /* null_treatement */
 							 PROVOLATILE_IMMUTABLE, /* volatility */
 							 PROPARALLEL_SAFE,	/* parallel safety */
 							 argtypes,	/* parameterTypes */
@@ -1886,6 +1888,7 @@ makeMultirangeConstructors(const char *name, Oid namespace,
 							 false, /* security_definer */
 							 false, /* leakproof */
 							 true,	/* isStrict */
+							 false,	/* null_treatement */
 							 PROVOLATILE_IMMUTABLE, /* volatility */
 							 PROPARALLEL_SAFE,	/* parallel safety */
 							 argtypes,	/* parameterTypes */
@@ -1926,6 +1929,7 @@ makeMultirangeConstructors(const char *name, Oid namespace,
 							 false, /* security_definer */
 							 false, /* leakproof */
 							 false, /* isStrict */
+							 false, /* null_treatment */
 							 PROVOLATILE_IMMUTABLE, /* volatility */
 							 PROPARALLEL_SAFE,	/* parallel safety */
 							 argtypes,	/* parameterTypes */
diff --git a/src/backend/executor/nodeWindowAgg.c b/src/backend/executor/nodeWindowAgg.c
index de58df3d3f..832b40b849 100644
--- a/src/backend/executor/nodeWindowAgg.c
+++ b/src/backend/executor/nodeWindowAgg.c
@@ -68,6 +68,7 @@ typedef struct WindowObjectData
 	int			readptr;		/* tuplestore read pointer for this fn */
 	int64		markpos;		/* row that markptr is positioned on */
 	int64		seekpos;		/* row that readptr is positioned on */
+	NullTreatment	null_treatment;	/* RESPECT/IGNORE NULLS? */
 } WindowObjectData;
 
 /*
@@ -2473,6 +2474,7 @@ ExecInitWindowAgg(WindowAgg *node, EState *estate, int eflags)
 			winobj->winstate = winstate;
 			winobj->argstates = wfuncstate->args;
 			winobj->localmem = NULL;
+			winobj->null_treatment = wfunc->winnulltreatment;
 			perfuncstate->winobj = winobj;
 
 			/* It's a real window function, so set up to call it. */
@@ -3173,48 +3175,103 @@ WinGetFuncArgInPartition(WindowObject winobj, int argno,
 	TupleTableSlot *slot;
 	bool		gottuple;
 	int64		abs_pos;
+	bool		ignore_nulls = false;
+	int			target = relpos;
+	int			step;
+	Datum		result;
 
 	Assert(WindowObjectIsValid(winobj));
 	winstate = winobj->winstate;
 	econtext = winstate->ss.ps.ps_ExprContext;
 	slot = winstate->temp_slot_1;
 
-	switch (seektype)
+	/*
+	 * If we're not ignoring nulls, we'll just go straight to the desired row.
+	 * But if we are ignoring nulls, we'll have to step towards the target row
+	 * by row so we need to determine how we get there.
+	 */
+	if (winobj->null_treatment == NULL_TREATMENT_IGNORE)
 	{
-		case WINDOW_SEEK_CURRENT:
-			abs_pos = winstate->currentpos + relpos;
-			break;
-		case WINDOW_SEEK_HEAD:
-			abs_pos = relpos;
-			break;
-		case WINDOW_SEEK_TAIL:
-			spool_tuples(winstate, -1);
-			abs_pos = winstate->spooled_rows - 1 + relpos;
-			break;
-		default:
-			elog(ERROR, "unrecognized window seek type: %d", seektype);
-			abs_pos = 0;		/* keep compiler quiet */
-			break;
-	}
-
-	gottuple = window_gettupleslot(winobj, abs_pos, slot);
+		ignore_nulls = true;
 
-	if (!gottuple)
-	{
-		if (isout)
-			*isout = true;
-		*isnull = true;
-		return (Datum) 0;
+		if (seektype == WINDOW_SEEK_HEAD)
+		{
+			step = 1;
+			relpos = 0;
+		}
+		else if (seektype == WINDOW_SEEK_TAIL)
+		{
+			step = -1;
+			relpos = 0;
+		}
+		else
+		{
+			if (target > 0)
+				step = 1;
+			else if (target < 0)
+				step = -1;
+			else
+				step = 0;
+			relpos = step;
+		}
 	}
-	else
+
+	for (;;)
 	{
-		if (isout)
-			*isout = false;
-		if (set_mark)
-			WinSetMarkPosition(winobj, abs_pos);
+		switch (seektype)
+		{
+			case WINDOW_SEEK_CURRENT:
+				abs_pos = winstate->currentpos + relpos;
+				break;
+			case WINDOW_SEEK_HEAD:
+				abs_pos = relpos;
+				break;
+			case WINDOW_SEEK_TAIL:
+				spool_tuples(winstate, -1);
+				abs_pos = winstate->spooled_rows - 1 + relpos;
+				break;
+			default:
+				elog(ERROR, "unrecognized window seek type: %d", seektype);
+				abs_pos = 0;		/* keep compiler quiet */
+				break;
+		}
+
+		gottuple = window_gettupleslot(winobj, abs_pos, slot);
+
+		/* Did we fall off the end of the partition? */
+		if (!gottuple)
+		{
+			if (isout)
+				*isout = true;
+			*isnull = true;
+			return (Datum) 0;
+		}
+
+		/* Evaluate the expression at this row */
 		econtext->ecxt_outertuple = slot;
-		return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
-							econtext, isnull);
+		result = ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
+							  econtext, isnull);
+
+		/* If we got a null and we're ignoring them, move the goalposts */
+		if (ignore_nulls && *isnull)
+			target += step;
+
+		/* Once we've reached our target, we're done */
+		if (relpos == target)
+		{
+			if (isout)
+				*isout = false;
+			/*
+			 * We can only mark the row if we're not ignoring nulls (because we
+			 * jump straight there).
+			 */
+			if (set_mark && !ignore_nulls)
+				WinSetMarkPosition(winobj, abs_pos);
+			return result;
+		}
+
+		/* Otherwise move closer and try again */
+		relpos += step;
 	}
 }
 
@@ -3261,170 +3318,218 @@ WinGetFuncArgInFrame(WindowObject winobj, int argno,
 	TupleTableSlot *slot;
 	int64		abs_pos;
 	int64		mark_pos;
+	bool		ignore_nulls = false;
+	int			target = relpos;
+	int			step;
+	Datum		result;
 
 	Assert(WindowObjectIsValid(winobj));
 	winstate = winobj->winstate;
 	econtext = winstate->ss.ps.ps_ExprContext;
 	slot = winstate->temp_slot_1;
 
-	switch (seektype)
+	/*
+	 * If we're not ignoring nulls, we'll just go straight to the desired row.
+	 * But if we are ignoring nulls, we'll have to step towards the target row
+	 * by row so we need to determine how we get there.
+	 */
+	if (winobj->null_treatment == NULL_TREATMENT_IGNORE)
 	{
-		case WINDOW_SEEK_CURRENT:
-			elog(ERROR, "WINDOW_SEEK_CURRENT is not supported for WinGetFuncArgInFrame");
-			abs_pos = mark_pos = 0; /* keep compiler quiet */
-			break;
-		case WINDOW_SEEK_HEAD:
-			/* rejecting relpos < 0 is easy and simplifies code below */
-			if (relpos < 0)
-				goto out_of_frame;
-			update_frameheadpos(winstate);
-			abs_pos = winstate->frameheadpos + relpos;
-			mark_pos = abs_pos;
+		ignore_nulls = true;
 
-			/*
-			 * Account for exclusion option if one is active, but advance only
-			 * abs_pos not mark_pos.  This prevents changes of the current
-			 * row's peer group from resulting in trying to fetch a row before
-			 * some previous mark position.
-			 *
-			 * Note that in some corner cases such as current row being
-			 * outside frame, these calculations are theoretically too simple,
-			 * but it doesn't matter because we'll end up deciding the row is
-			 * out of frame.  We do not attempt to avoid fetching rows past
-			 * end of frame; that would happen in some cases anyway.
-			 */
-			switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
-			{
-				case 0:
-					/* no adjustment needed */
-					break;
-				case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
-					if (abs_pos >= winstate->currentpos &&
-						winstate->currentpos >= winstate->frameheadpos)
-						abs_pos++;
-					break;
-				case FRAMEOPTION_EXCLUDE_GROUP:
-					update_grouptailpos(winstate);
-					if (abs_pos >= winstate->groupheadpos &&
-						winstate->grouptailpos > winstate->frameheadpos)
-					{
-						int64		overlapstart = Max(winstate->groupheadpos,
-													   winstate->frameheadpos);
+		if (target > 0)
+			step = 1;
+		else if (target < 0)
+			step = -1;
+		else if (seektype == WINDOW_SEEK_HEAD)
+			step = 1;
+		else if (seektype == WINDOW_SEEK_TAIL)
+			step = -1;
+		else
+			step = 0;
 
-						abs_pos += winstate->grouptailpos - overlapstart;
-					}
-					break;
-				case FRAMEOPTION_EXCLUDE_TIES:
-					update_grouptailpos(winstate);
-					if (abs_pos >= winstate->groupheadpos &&
-						winstate->grouptailpos > winstate->frameheadpos)
-					{
-						int64		overlapstart = Max(winstate->groupheadpos,
-													   winstate->frameheadpos);
+		relpos = 0;
+	}
 
-						if (abs_pos == overlapstart)
-							abs_pos = winstate->currentpos;
-						else
-							abs_pos += winstate->grouptailpos - overlapstart - 1;
-					}
-					break;
-				default:
-					elog(ERROR, "unrecognized frame option state: 0x%x",
-						 winstate->frameOptions);
-					break;
-			}
-			break;
-		case WINDOW_SEEK_TAIL:
-			/* rejecting relpos > 0 is easy and simplifies code below */
-			if (relpos > 0)
-				goto out_of_frame;
-			update_frametailpos(winstate);
-			abs_pos = winstate->frametailpos - 1 + relpos;
+	for (;;)
+	{
+		switch (seektype)
+		{
+			case WINDOW_SEEK_CURRENT:
+				elog(ERROR, "WINDOW_SEEK_CURRENT is not supported for WinGetFuncArgInFrame");
+				abs_pos = mark_pos = 0; /* keep compiler quiet */
+				break;
+			case WINDOW_SEEK_HEAD:
+				/* rejecting relpos < 0 is easy and simplifies code below */
+				if (relpos < 0)
+					goto out_of_frame;
+				update_frameheadpos(winstate);
+				abs_pos = winstate->frameheadpos + relpos;
+				mark_pos = abs_pos;
 
-			/*
-			 * Account for exclusion option if one is active.  If there is no
-			 * exclusion, we can safely set the mark at the accessed row.  But
-			 * if there is, we can only mark the frame start, because we can't
-			 * be sure how far back in the frame the exclusion might cause us
-			 * to fetch in future.  Furthermore, we have to actually check
-			 * against frameheadpos here, since it's unsafe to try to fetch a
-			 * row before frame start if the mark might be there already.
-			 */
-			switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
-			{
-				case 0:
-					/* no adjustment needed */
-					mark_pos = abs_pos;
-					break;
-				case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
-					if (abs_pos <= winstate->currentpos &&
-						winstate->currentpos < winstate->frametailpos)
-						abs_pos--;
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				case FRAMEOPTION_EXCLUDE_GROUP:
-					update_grouptailpos(winstate);
-					if (abs_pos < winstate->grouptailpos &&
-						winstate->groupheadpos < winstate->frametailpos)
-					{
-						int64		overlapend = Min(winstate->grouptailpos,
-													 winstate->frametailpos);
+				/*
+				 * Account for exclusion option if one is active, but advance only
+				 * abs_pos not mark_pos.  This prevents changes of the current
+				 * row's peer group from resulting in trying to fetch a row before
+				 * some previous mark position.
+				 *
+				 * Note that in some corner cases such as current row being
+				 * outside frame, these calculations are theoretically too simple,
+				 * but it doesn't matter because we'll end up deciding the row is
+				 * out of frame.  We do not attempt to avoid fetching rows past
+				 * end of frame; that would happen in some cases anyway.
+				 */
+				switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
+				{
+					case 0:
+						/* no adjustment needed */
+						break;
+					case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
+						if (abs_pos >= winstate->currentpos &&
+							winstate->currentpos >= winstate->frameheadpos)
+							abs_pos++;
+						break;
+					case FRAMEOPTION_EXCLUDE_GROUP:
+						update_grouptailpos(winstate);
+						if (abs_pos >= winstate->groupheadpos &&
+							winstate->grouptailpos > winstate->frameheadpos)
+						{
+							int64		overlapstart = Max(winstate->groupheadpos,
+														   winstate->frameheadpos);
+
+							abs_pos += winstate->grouptailpos - overlapstart;
+						}
+						break;
+					case FRAMEOPTION_EXCLUDE_TIES:
+						update_grouptailpos(winstate);
+						if (abs_pos >= winstate->groupheadpos &&
+							winstate->grouptailpos > winstate->frameheadpos)
+						{
+							int64		overlapstart = Max(winstate->groupheadpos,
+														   winstate->frameheadpos);
+
+							if (abs_pos == overlapstart)
+								abs_pos = winstate->currentpos;
+							else
+								abs_pos += winstate->grouptailpos - overlapstart - 1;
+						}
+						break;
+					default:
+						elog(ERROR, "unrecognized frame option state: 0x%x",
+							 winstate->frameOptions);
+						break;
+				}
+				break;
+			case WINDOW_SEEK_TAIL:
+				/* rejecting relpos > 0 is easy and simplifies code below */
+				if (relpos > 0)
+					goto out_of_frame;
+				update_frametailpos(winstate);
+				abs_pos = winstate->frametailpos - 1 + relpos;
 
-						abs_pos -= overlapend - winstate->groupheadpos;
-					}
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				case FRAMEOPTION_EXCLUDE_TIES:
-					update_grouptailpos(winstate);
-					if (abs_pos < winstate->grouptailpos &&
-						winstate->groupheadpos < winstate->frametailpos)
-					{
-						int64		overlapend = Min(winstate->grouptailpos,
-													 winstate->frametailpos);
+				/*
+				 * Account for exclusion option if one is active.  If there is no
+				 * exclusion, we can safely set the mark at the accessed row.  But
+				 * if there is, we can only mark the frame start, because we can't
+				 * be sure how far back in the frame the exclusion might cause us
+				 * to fetch in future.  Furthermore, we have to actually check
+				 * against frameheadpos here, since it's unsafe to try to fetch a
+				 * row before frame start if the mark might be there already.
+				 */
+				switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
+				{
+					case 0:
+						/* no adjustment needed */
+						mark_pos = abs_pos;
+						break;
+					case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
+						if (abs_pos <= winstate->currentpos &&
+							winstate->currentpos < winstate->frametailpos)
+							abs_pos--;
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					case FRAMEOPTION_EXCLUDE_GROUP:
+						update_grouptailpos(winstate);
+						if (abs_pos < winstate->grouptailpos &&
+							winstate->groupheadpos < winstate->frametailpos)
+						{
+							int64		overlapend = Min(winstate->grouptailpos,
+														 winstate->frametailpos);
+
+							abs_pos -= overlapend - winstate->groupheadpos;
+						}
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					case FRAMEOPTION_EXCLUDE_TIES:
+						update_grouptailpos(winstate);
+						if (abs_pos < winstate->grouptailpos &&
+							winstate->groupheadpos < winstate->frametailpos)
+						{
+							int64		overlapend = Min(winstate->grouptailpos,
+														 winstate->frametailpos);
+
+							if (abs_pos == overlapend - 1)
+								abs_pos = winstate->currentpos;
+							else
+								abs_pos -= overlapend - 1 - winstate->groupheadpos;
+						}
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					default:
+						elog(ERROR, "unrecognized frame option state: 0x%x",
+							 winstate->frameOptions);
+						mark_pos = 0;	/* keep compiler quiet */
+						break;
+				}
+				break;
+			default:
+				elog(ERROR, "unrecognized window seek type: %d", seektype);
+				abs_pos = mark_pos = 0; /* keep compiler quiet */
+				break;
+		}
 
-						if (abs_pos == overlapend - 1)
-							abs_pos = winstate->currentpos;
-						else
-							abs_pos -= overlapend - 1 - winstate->groupheadpos;
-					}
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				default:
-					elog(ERROR, "unrecognized frame option state: 0x%x",
-						 winstate->frameOptions);
-					mark_pos = 0;	/* keep compiler quiet */
-					break;
-			}
-			break;
-		default:
-			elog(ERROR, "unrecognized window seek type: %d", seektype);
-			abs_pos = mark_pos = 0; /* keep compiler quiet */
-			break;
-	}
+		if (!window_gettupleslot(winobj, abs_pos, slot))
+			goto out_of_frame;
 
-	if (!window_gettupleslot(winobj, abs_pos, slot))
-		goto out_of_frame;
+		/* The code above does not detect all out-of-frame cases, so check */
+		if (row_is_in_frame(winstate, abs_pos, slot) <= 0)
+			goto out_of_frame;
 
-	/* The code above does not detect all out-of-frame cases, so check */
-	if (row_is_in_frame(winstate, abs_pos, slot) <= 0)
-		goto out_of_frame;
+		/* Evaluate the expression at this row */
+		econtext->ecxt_outertuple = slot;
+		result = ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
+							  econtext, isnull);
 
-	if (isout)
-		*isout = false;
-	if (set_mark)
-		WinSetMarkPosition(winobj, mark_pos);
-	econtext->ecxt_outertuple = slot;
-	return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
-						econtext, isnull);
+		/* If we got a null and we're ignoring them, move the goalposts */
+		if (ignore_nulls && *isnull)
+			target += step;
+
+		/* Once we've reached our target, we're done */
+		if (relpos == target)
+		{
+			if (isout)
+				*isout = false;
+			/*
+			 * We can only mark the row if we're not ignoring nulls (because we
+			 * jump straight there).
+			 */
+			if (set_mark && !ignore_nulls)
+				WinSetMarkPosition(winobj, mark_pos);
+			return result;
+		}
+
+		/* Otherwise move closer and try again */
+		relpos += step;
+	}
 
 out_of_frame:
 	if (isout)
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 70f8b718e0..eba1f3f4d2 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -1533,6 +1533,7 @@ _copyWindowFunc(const WindowFunc *from)
 	COPY_SCALAR_FIELD(winref);
 	COPY_SCALAR_FIELD(winstar);
 	COPY_SCALAR_FIELD(winagg);
+	COPY_SCALAR_FIELD(winnulltreatment);
 	COPY_LOCATION_FIELD(location);
 
 	return newnode;
@@ -2691,6 +2692,7 @@ _copyFuncCall(const FuncCall *from)
 	COPY_SCALAR_FIELD(agg_distinct);
 	COPY_SCALAR_FIELD(func_variadic);
 	COPY_SCALAR_FIELD(funcformat);
+	COPY_SCALAR_FIELD(win_null_treatment);
 	COPY_LOCATION_FIELD(location);
 
 	return newnode;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 541e0e6b48..effed2f811 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -266,6 +266,7 @@ _equalWindowFunc(const WindowFunc *a, const WindowFunc *b)
 	COMPARE_SCALAR_FIELD(winref);
 	COMPARE_SCALAR_FIELD(winstar);
 	COMPARE_SCALAR_FIELD(winagg);
+	COMPARE_SCALAR_FIELD(winnulltreatment);
 	COMPARE_LOCATION_FIELD(location);
 
 	return true;
@@ -2380,6 +2381,7 @@ _equalFuncCall(const FuncCall *a, const FuncCall *b)
 	COMPARE_SCALAR_FIELD(agg_distinct);
 	COMPARE_SCALAR_FIELD(func_variadic);
 	COMPARE_SCALAR_FIELD(funcformat);
+	COMPARE_SCALAR_FIELD(win_null_treatment);
 	COMPARE_LOCATION_FIELD(location);
 
 	return true;
diff --git a/src/backend/nodes/makefuncs.c b/src/backend/nodes/makefuncs.c
index ee033ae779..587cd43e6b 100644
--- a/src/backend/nodes/makefuncs.c
+++ b/src/backend/nodes/makefuncs.c
@@ -596,6 +596,7 @@ makeFuncCall(List *name, List *args, CoercionForm funcformat, int location)
 	n->agg_distinct = false;
 	n->func_variadic = false;
 	n->funcformat = funcformat;
+	n->win_null_treatment = NULL_TREATMENT_NONE;
 	n->location = location;
 	return n;
 }
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index d78b16ed1d..164751a357 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -1184,6 +1184,7 @@ _outWindowFunc(StringInfo str, const WindowFunc *node)
 	WRITE_UINT_FIELD(winref);
 	WRITE_BOOL_FIELD(winstar);
 	WRITE_BOOL_FIELD(winagg);
+	WRITE_INT_FIELD(winnulltreatment);
 	WRITE_LOCATION_FIELD(location);
 }
 
@@ -2790,6 +2791,7 @@ _outFuncCall(StringInfo str, const FuncCall *node)
 	WRITE_BOOL_FIELD(agg_distinct);
 	WRITE_BOOL_FIELD(func_variadic);
 	WRITE_ENUM_FIELD(funcformat, CoercionForm);
+	WRITE_BOOL_FIELD(win_null_treatment);
 	WRITE_LOCATION_FIELD(location);
 }
 
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index 0f6a77afc4..587757f2c9 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -656,6 +656,7 @@ _readWindowFunc(void)
 	READ_UINT_FIELD(winref);
 	READ_BOOL_FIELD(winstar);
 	READ_BOOL_FIELD(winagg);
+	READ_INT_FIELD(winnulltreatment);
 	READ_LOCATION_FIELD(location);
 
 	READ_DONE();
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 8f5cbf99f4..85ea709d81 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -2221,6 +2221,7 @@ eval_const_expressions_mutator(Node *node,
 				newexpr->winref = expr->winref;
 				newexpr->winstar = expr->winstar;
 				newexpr->winagg = expr->winagg;
+				newexpr->winnulltreatment = expr->winnulltreatment;
 				newexpr->location = expr->location;
 
 				return (Node *) newexpr;
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 8f341ac006..59d72207c9 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -582,6 +582,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <list>	window_clause window_definition_list opt_partition_clause
 %type <windef>	window_definition over_clause window_specification
 				opt_frame_clause frame_extent frame_bound
+%type <ival>	null_treatment
 %type <ival>	opt_window_exclusion_clause
 %type <str>		opt_existing_window_name
 %type <boolean> opt_if_not_exists
@@ -650,7 +651,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 	HANDLER HAVING HEADER_P HOLD HOUR_P
 
-	IDENTITY_P IF_P ILIKE IMMEDIATE IMMUTABLE IMPLICIT_P IMPORT_P IN_P INCLUDE
+	IDENTITY_P IF_P IGNORE_P ILIKE IMMEDIATE IMMUTABLE IMPLICIT_P IMPORT_P IN_P INCLUDE
 	INCLUDING INCREMENT INDEX INDEXES INHERIT INHERITS INITIALLY INLINE_P
 	INNER_P INOUT INPUT_P INSENSITIVE INSERT INSTEAD INT_P INTEGER
 	INTERSECT INTERVAL INTO INVOKER IS ISNULL ISOLATION
@@ -682,7 +683,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 	RANGE READ REAL REASSIGN RECHECK RECURSIVE REF REFERENCES REFERENCING
 	REFRESH REINDEX RELATIVE_P RELEASE RENAME REPEATABLE REPLACE REPLICA
-	RESET RESTART RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROLLUP
+	RESET RESPECT RESTART RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROLLUP
 	ROUTINE ROUTINES ROW ROWS RULE
 
 	SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
@@ -7799,6 +7800,10 @@ createfunc_opt_item:
 				{
 					$$ = makeDefElem("window", (Node *)makeInteger(true), @1);
 				}
+			| TREAT NULLS_P
+				{
+					$$ = makeDefElem("null_treatment", (Node *)makeInteger(true), @1);
+				}
 			| common_func_opt_item
 				{
 					$$ = $1;
@@ -13676,6 +13681,14 @@ func_expr: func_application within_group_clause filter_clause over_clause
 					}
 					n->agg_filter = $3;
 					n->over = $4;
+					n->win_null_treatment = NULL_TREATMENT_NONE;
+					$$ = (Node *) n;
+				}
+			| func_application null_treatment over_clause
+				{
+					FuncCall *n = (FuncCall *) $1;
+					n->over = $3;
+					n->win_null_treatment = $2;
 					$$ = (Node *) n;
 				}
 			| func_expr_common_subexpr
@@ -14096,6 +14109,11 @@ window_definition:
 				}
 		;
 
+null_treatment:
+			IGNORE_P NULLS_P	{ $$ = NULL_TREATMENT_IGNORE; }
+			| RESPECT NULLS_P	{ $$ = NULL_TREATMENT_RESPECT; }
+		;
+
 over_clause: OVER window_specification
 				{ $$ = $2; }
 			| OVER ColId
@@ -15177,6 +15195,7 @@ unreserved_keyword:
 			| HOUR_P
 			| IDENTITY_P
 			| IF_P
+			| IGNORE_P
 			| IMMEDIATE
 			| IMMUTABLE
 			| IMPLICIT_P
@@ -15283,6 +15302,7 @@ unreserved_keyword:
 			| REPLACE
 			| REPLICA
 			| RESET
+			| RESPECT
 			| RESTART
 			| RESTRICT
 			| RETURNS
diff --git a/src/backend/parser/parse_func.c b/src/backend/parser/parse_func.c
index 23ac2a2fe6..b42850f91e 100644
--- a/src/backend/parser/parse_func.c
+++ b/src/backend/parser/parse_func.c
@@ -97,6 +97,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 	bool		agg_distinct = (fn ? fn->agg_distinct : false);
 	bool		func_variadic = (fn ? fn->func_variadic : false);
 	CoercionForm funcformat = (fn ? fn->funcformat : COERCE_EXPLICIT_CALL);
+	NullTreatment	win_null_treatment = (fn ? fn->win_null_treatment : NULL_TREATMENT_NONE);
 	bool		could_be_projection;
 	Oid			rettype;
 	Oid			funcid;
@@ -108,6 +109,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 	Oid		   *declared_arg_types;
 	List	   *argnames;
 	List	   *argdefaults;
+	bool		null_treatment;
 	Node	   *retval;
 	bool		retset;
 	int			nvargs;
@@ -267,7 +269,8 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 							   !func_variadic, true,
 							   &funcid, &rettype, &retset,
 							   &nvargs, &vatype,
-							   &declared_arg_types, &argdefaults);
+							   &declared_arg_types, &argdefaults,
+							   &null_treatment);
 
 	cancel_parser_errposition_callback(&pcbstate);
 
@@ -507,6 +510,13 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 						 errmsg("%s is not an ordered-set aggregate, so it cannot have WITHIN GROUP",
 								NameListToString(funcname)),
 						 parser_errposition(pstate, location)));
+
+			/* It also can't treat nulls as a window function */
+			if (over && win_null_treatment != NULL_TREATMENT_NONE)
+				ereport(ERROR,
+						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+						 errmsg("aggregate functions do not accept RESPECT/IGNORE NULLS"),
+						 parser_errposition(pstate, location)));
 		}
 	}
 	else if (fdresult == FUNCDETAIL_WINDOWFUNC)
@@ -527,6 +537,13 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 					 errmsg("window function %s cannot have WITHIN GROUP",
 							NameListToString(funcname)),
 					 parser_errposition(pstate, location)));
+
+		if (!null_treatment && win_null_treatment != NULL_TREATMENT_NONE)
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("window function %s does not accept RESPECT/IGNORE NULLS",
+							NameListToString(funcname)),
+					 parser_errposition(pstate, location)));
 	}
 	else if (fdresult == FUNCDETAIL_COERCION)
 	{
@@ -826,6 +843,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 		wfunc->winstar = agg_star;
 		wfunc->winagg = (fdresult == FUNCDETAIL_AGGREGATE);
 		wfunc->aggfilter = agg_filter;
+		wfunc->winnulltreatment = win_null_treatment;
 		wfunc->location = location;
 
 		/*
@@ -1396,7 +1414,8 @@ func_get_detail(List *funcname,
 				int *nvargs,	/* return value */
 				Oid *vatype,	/* return value */
 				Oid **true_typeids, /* return value */
-				List **argdefaults) /* optional return value */
+				List **argdefaults, /* optional return value */
+				bool *null_treatment) /* optional return value */
 {
 	FuncCandidateList raw_candidates;
 	FuncCandidateList best_candidate;
@@ -1410,6 +1429,8 @@ func_get_detail(List *funcname,
 	*true_typeids = NULL;
 	if (argdefaults)
 		*argdefaults = NIL;
+	if (null_treatment)
+		*null_treatment = NULL_TREATMENT_NONE;
 
 	/* Get list of possible candidates from namespace search */
 	raw_candidates = FuncnameGetCandidates(funcname, nargs, fargnames,
@@ -1687,6 +1708,8 @@ func_get_detail(List *funcname,
 				*argdefaults = defaults;
 			}
 		}
+		if (null_treatment)
+			*null_treatment = pform->pronulltreatment;
 
 		switch (pform->prokind)
 		{
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 7d4443e807..9e41b61c08 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -2660,6 +2660,9 @@ pg_get_functiondef(PG_FUNCTION_ARGS)
 
 	if (proc->prokind == PROKIND_WINDOW)
 		appendStringInfoString(&buf, " WINDOW");
+	if (proc->pronulltreatment)
+		appendStringInfoString(&buf, " TREAT NULLS");
+
 	switch (proc->provolatile)
 	{
 		case PROVOLATILE_IMMUTABLE:
@@ -9474,7 +9477,12 @@ get_windowfunc_expr(WindowFunc *wfunc, deparse_context *context)
 		get_rule_expr((Node *) wfunc->aggfilter, context, false);
 	}
 
-	appendStringInfoString(buf, ") OVER ");
+	if (wfunc->winnulltreatment == NULL_TREATMENT_IGNORE)
+		appendStringInfoString(buf, ") IGNORE NULLS OVER ");
+	else if (wfunc->winnulltreatment == NULL_TREATMENT_RESPECT)
+		appendStringInfoString(buf, ") RESPECT NULLS OVER ");
+	else
+		appendStringInfoString(buf, ") OVER ");
 
 	foreach(l, context->windowClause)
 	{
@@ -11227,7 +11235,7 @@ generate_function_name(Oid funcid, int nargs, List *argnames, Oid *argtypes,
 								   !use_variadic, true,
 								   &p_funcid, &p_rettype,
 								   &p_retset, &p_nvargs, &p_vatype,
-								   &p_true_typeids, NULL);
+								   &p_true_typeids, NULL, NULL);
 	else
 	{
 		p_result = FUNCDETAIL_NOTFOUND;
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 139f4a08bd..50c7b47be2 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -9770,33 +9770,42 @@
   proargtypes => 'int4', prosrc => 'window_ntile' },
 { oid => '3106', descr => 'fetch the preceding row value',
   proname => 'lag', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_lag' },
+  proargtypes => 'anyelement', prosrc => 'window_lag',
+  pronulltreatment => 't' },
 { oid => '3107', descr => 'fetch the Nth preceding row value',
   proname => 'lag', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_lag_with_offset' },
+  proargtypes => 'anyelement int4', prosrc => 'window_lag_with_offset',
+  pronulltreatment => 't' },
 { oid => '3108', descr => 'fetch the Nth preceding row value with default',
   proname => 'lag', prokind => 'w', prorettype => 'anycompatible',
   proargtypes => 'anycompatible int4 anycompatible',
-  prosrc => 'window_lag_with_offset_and_default' },
+  prosrc => 'window_lag_with_offset_and_default',
+  pronulltreatment => 't' },
 { oid => '3109', descr => 'fetch the following row value',
   proname => 'lead', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_lead' },
+  proargtypes => 'anyelement', prosrc => 'window_lead',
+  pronulltreatment => 't' },
 { oid => '3110', descr => 'fetch the Nth following row value',
   proname => 'lead', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_lead_with_offset' },
+  proargtypes => 'anyelement int4', prosrc => 'window_lead_with_offset',
+  pronulltreatment => 't' },
 { oid => '3111', descr => 'fetch the Nth following row value with default',
   proname => 'lead', prokind => 'w', prorettype => 'anycompatible',
   proargtypes => 'anycompatible int4 anycompatible',
-  prosrc => 'window_lead_with_offset_and_default' },
+  prosrc => 'window_lead_with_offset_and_default',
+  pronulltreatment => 't' },
 { oid => '3112', descr => 'fetch the first row value',
   proname => 'first_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_first_value' },
+  proargtypes => 'anyelement', prosrc => 'window_first_value',
+  pronulltreatment => 't' },
 { oid => '3113', descr => 'fetch the last row value',
   proname => 'last_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_last_value' },
+  proargtypes => 'anyelement', prosrc => 'window_last_value',
+  pronulltreatment => 't' },
 { oid => '3114', descr => 'fetch the Nth row value',
   proname => 'nth_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_nth_value' },
+  proargtypes => 'anyelement int4', prosrc => 'window_nth_value',
+  pronulltreatment => 't' },
 
 # functions for range types
 { oid => '3832', descr => 'I/O',
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index f8e6dea22d..31d1dfd465 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -67,6 +67,9 @@ CATALOG(pg_proc,1255,ProcedureRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(81,Proce
 	/* strict with respect to NULLs? */
 	bool		proisstrict BKI_DEFAULT(t);
 
+	/* can handle IGNORE/RESPECT NULLS? (must be window function) */
+	bool		pronulltreatment BKI_DEFAULT(f);
+
 	/* returns a set? */
 	bool		proretset BKI_DEFAULT(f);
 
@@ -198,6 +201,7 @@ extern ObjectAddress ProcedureCreate(const char *procedureName,
 									 bool security_definer,
 									 bool isLeakProof,
 									 bool isStrict,
+									 bool null_treatment,
 									 char volatility,
 									 char parallel,
 									 oidvector *parameterTypes,
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 48a79a7657..c3dd64d96d 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -357,6 +357,7 @@ typedef struct FuncCall
 	bool		agg_distinct;	/* arguments were labeled DISTINCT */
 	bool		func_variadic;	/* last argument was labeled VARIADIC */
 	CoercionForm funcformat;	/* how to display this node */
+	NullTreatment	win_null_treatment;	/* IGNORE NULLS or RESPECT NULLS? */
 	int			location;		/* token location, or -1 if unknown */
 } FuncCall;
 
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index dd85908fe2..6426c07777 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -52,6 +52,13 @@ typedef enum OnCommitAction
 	ONCOMMIT_DROP				/* ON COMMIT DROP */
 } OnCommitAction;
 
+typedef enum NullTreatment
+{
+	NULL_TREATMENT_NONE = 0,
+	NULL_TREATMENT_RESPECT,
+	NULL_TREATMENT_IGNORE
+} NullTreatment;
+
 /*
  * RangeVar - range variable, used in FROM clauses
  *
@@ -387,6 +394,7 @@ typedef struct WindowFunc
 	Index		winref;			/* index of associated WindowClause */
 	bool		winstar;		/* true if argument list was really '*' */
 	bool		winagg;			/* is function a simple aggregate? */
+	NullTreatment	winnulltreatment;	/* can accept RESPECT/IGNORE NULLS? */
 	int			location;		/* token location, or -1 if unknown */
 } WindowFunc;
 
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 71dcdf2889..b288422fda 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -190,6 +190,7 @@ PG_KEYWORD("hold", HOLD, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("hour", HOUR_P, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("identity", IDENTITY_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("if", IF_P, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("ignore", IGNORE_P, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("ilike", ILIKE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("immediate", IMMEDIATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("immutable", IMMUTABLE, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -342,6 +343,7 @@ PG_KEYWORD("repeatable", REPEATABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("replace", REPLACE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("replica", REPLICA, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("reset", RESET, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("respect", RESPECT, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("restart", RESTART, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("restrict", RESTRICT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("returning", RETURNING, RESERVED_KEYWORD, AS_LABEL)
diff --git a/src/include/parser/parse_func.h b/src/include/parser/parse_func.h
index dd189f5452..ead6241525 100644
--- a/src/include/parser/parse_func.h
+++ b/src/include/parser/parse_func.h
@@ -41,7 +41,8 @@ extern FuncDetailCode func_get_detail(List *funcname,
 									  bool expand_variadic, bool expand_defaults,
 									  Oid *funcid, Oid *rettype,
 									  bool *retset, int *nvargs, Oid *vatype,
-									  Oid **true_typeids, List **argdefaults);
+									  Oid **true_typeids, List **argdefaults,
+									  bool *null_treatment);
 
 extern int	func_match_argtypes(int nargs,
 								Oid *input_typeids,
diff --git a/src/test/regress/expected/create_function_3.out b/src/test/regress/expected/create_function_3.out
index ce508ae1dc..0311f8ecc9 100644
--- a/src/test/regress/expected/create_function_3.out
+++ b/src/test/regress/expected/create_function_3.out
@@ -122,6 +122,12 @@ SELECT proname, prosecdef FROM pg_proc
  functest_c_3 | t
 (3 rows)
 
+--
+-- TREAT NULLS
+--
+CREATE FUNCTION functest_D_1(integer) RETURNS integer LANGUAGE 'sql'
+       TREAT NULLS AS 'SELECT $1';
+ERROR:  cannot set null treatment on a non-window function
 --
 -- LEAKPROOF
 --
@@ -298,6 +304,8 @@ CREATE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL AS 'SELECT $1';
 CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL WINDOW AS 'SELECT $1';
 ERROR:  cannot change routine kind
 DETAIL:  "functest1" is a function.
+CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL TREAT NULLS AS 'SELECT $1';
+ERROR:  cannot set null treatment on a non-window function
 CREATE OR REPLACE PROCEDURE functest1(a int) LANGUAGE SQL AS 'SELECT $1';
 ERROR:  cannot change routine kind
 DETAIL:  "functest1" is a function.
diff --git a/src/test/regress/expected/create_procedure.out b/src/test/regress/expected/create_procedure.out
index 3838fa2324..f81f9b79cc 100644
--- a/src/test/regress/expected/create_procedure.out
+++ b/src/test/regress/expected/create_procedure.out
@@ -174,6 +174,10 @@ CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT INTO cp_test VALUES (
 ERROR:  invalid attribute in procedure definition
 LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT I...
                                                ^
+CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
+ERROR:  invalid attribute in procedure definition
+LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INS...
+                                               ^
 CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 ERROR:  invalid attribute in procedure definition
 LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT I...
diff --git a/src/test/regress/expected/misc_sanity.out b/src/test/regress/expected/misc_sanity.out
index d40afeef78..8615d78075 100644
--- a/src/test/regress/expected/misc_sanity.out
+++ b/src/test/regress/expected/misc_sanity.out
@@ -109,3 +109,13 @@ ORDER BY 1, 2;
  pg_largeobject_metadata | lomacl        | aclitem[]
 (11 rows)
 
+-- **************** pg_class ****************
+-- Look for non-window functions with null treatment (there should be none)
+SELECT proname, prokind, pronulltreatment
+FROM pg_proc
+WHERE pronulltreatment AND prokind <> 'w'
+ORDER BY oid;
+ proname | prokind | pronulltreatment 
+---------+---------+------------------
+(0 rows)
+
diff --git a/src/test/regress/expected/window.out b/src/test/regress/expected/window.out
index 19e2ac518a..3bd9584c6c 100644
--- a/src/test/regress/expected/window.out
+++ b/src/test/regress/expected/window.out
@@ -4063,3 +4063,214 @@ SELECT * FROM pg_temp.f(2);
  {5}
 (5 rows)
 
+-- IGNORE NULLS tests
+CREATE TEMPORARY TABLE planets (
+    name text,
+    orbit integer
+);
+INSERT INTO planets VALUES
+  ('mercury', 88),
+  ('venus', 224),
+  ('earth', NULL),
+  ('mars', NULL),
+  ('jupiter', 4332),
+  ('saturn', 24491),
+  ('uranus', NULL),
+  ('neptune', 60182),
+  ('pluto', 90560),
+  ('xyzzy', NULL);
+-- test ruleutils
+CREATE VIEW planets_view AS
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+NOTICE:  view "planets_view" will be a temporary view
+SELECT pg_get_viewdef('planets_view');
+                       pg_get_viewdef                        
+-------------------------------------------------------------
+  SELECT planets.name,                                      +
+     planets.orbit,                                         +
+     lag(planets.orbit) OVER w AS lag,                      +
+     lag(planets.orbit) RESPECT NULLS OVER w AS lag_respect,+
+     lag(planets.orbit) IGNORE NULLS OVER w AS lag_ignore   +
+    FROM planets                                            +
+   WINDOW w AS (ORDER BY planets.name);
+(1 row)
+
+-- lag
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+  name   | orbit |  lag  | lag_respect | lag_ignore 
+---------+-------+-------+-------------+------------
+ earth   |       |       |             |           
+ jupiter |  4332 |       |             |           
+ mars    |       |  4332 |        4332 |       4332
+ mercury |    88 |       |             |       4332
+ neptune | 60182 |    88 |          88 |         88
+ pluto   | 90560 | 60182 |       60182 |      60182
+ saturn  | 24491 | 90560 |       90560 |      90560
+ uranus  |       | 24491 |       24491 |      24491
+ venus   |   224 |       |             |      24491
+ xyzzy   |       |   224 |         224 |        224
+(10 rows)
+
+-- lead
+SELECT name,
+       orbit,
+       lead(orbit) OVER w AS lead,
+       lead(orbit) RESPECT NULLS OVER w AS lead_respect,
+       lead(orbit) IGNORE NULLS OVER w AS lead_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+  name   | orbit | lead  | lead_respect | lead_ignore 
+---------+-------+-------+--------------+-------------
+ earth   |       |  4332 |         4332 |        4332
+ jupiter |  4332 |       |              |          88
+ mars    |       |    88 |           88 |          88
+ mercury |    88 | 60182 |        60182 |       60182
+ neptune | 60182 | 90560 |        90560 |       90560
+ pluto   | 90560 | 24491 |        24491 |       24491
+ saturn  | 24491 |       |              |         224
+ uranus  |       |   224 |          224 |         224
+ venus   |   224 |       |              |            
+ xyzzy   |       |       |              |            
+(10 rows)
+
+-- first_value
+SELECT name,
+       orbit,
+       first_value(orbit) RESPECT NULLS OVER w1,
+       first_value(orbit) IGNORE NULLS OVER w1,
+       first_value(orbit) RESPECT NULLS OVER w2,
+       first_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | first_value | first_value | first_value | first_value 
+---------+-------+-------------+-------------+-------------+-------------
+ earth   |       |             |        4332 |             |        4332
+ jupiter |  4332 |             |        4332 |             |        4332
+ mars    |       |             |        4332 |             |        4332
+ mercury |    88 |             |        4332 |        4332 |        4332
+ neptune | 60182 |             |        4332 |             |          88
+ pluto   | 90560 |             |        4332 |          88 |          88
+ saturn  | 24491 |             |        4332 |       60182 |       60182
+ uranus  |       |             |        4332 |       90560 |       90560
+ venus   |   224 |             |        4332 |       24491 |       24491
+ xyzzy   |       |             |        4332 |             |         224
+(10 rows)
+
+-- nth_value
+SELECT name,
+       orbit,
+       nth_value(orbit, 2) RESPECT NULLS OVER w1,
+       nth_value(orbit, 2) IGNORE NULLS OVER w1,
+       nth_value(orbit, 2) RESPECT NULLS OVER w2,
+       nth_value(orbit, 2) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | nth_value | nth_value | nth_value | nth_value 
+---------+-------+-----------+-----------+-----------+-----------
+ earth   |       |      4332 |        88 |      4332 |          
+ jupiter |  4332 |      4332 |        88 |      4332 |        88
+ mars    |       |      4332 |        88 |      4332 |        88
+ mercury |    88 |      4332 |        88 |           |        88
+ neptune | 60182 |      4332 |        88 |        88 |     60182
+ pluto   | 90560 |      4332 |        88 |     60182 |     60182
+ saturn  | 24491 |      4332 |        88 |     90560 |     90560
+ uranus  |       |      4332 |        88 |     24491 |     24491
+ venus   |   224 |      4332 |        88 |           |       224
+ xyzzy   |       |      4332 |        88 |       224 |          
+(10 rows)
+
+-- last_value
+SELECT name,
+       orbit,
+       last_value(orbit) RESPECT NULLS OVER w1,
+       last_value(orbit) IGNORE NULLS OVER w1,
+       last_value(orbit) RESPECT NULLS OVER w2,
+       last_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | last_value | last_value | last_value | last_value 
+---------+-------+------------+------------+------------+------------
+ earth   |       |            |        224 |            |       4332
+ jupiter |  4332 |            |        224 |         88 |         88
+ mars    |       |            |        224 |      60182 |      60182
+ mercury |    88 |            |        224 |      90560 |      90560
+ neptune | 60182 |            |        224 |      24491 |      24491
+ pluto   | 90560 |            |        224 |            |      24491
+ saturn  | 24491 |            |        224 |        224 |        224
+ uranus  |       |            |        224 |            |        224
+ venus   |   224 |            |        224 |            |        224
+ xyzzy   |       |            |        224 |            |        224
+(10 rows)
+
+-- window function without null treatment
+SELECT row_number() OVER (ORDER BY name) FROM planets;
+ row_number 
+------------
+          1
+          2
+          3
+          4
+          5
+          6
+          7
+          8
+          9
+         10
+(10 rows)
+
+SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM planets; -- fails
+ERROR:  window function row_number does not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM ...
+               ^
+SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM planets; -- fails
+ERROR:  window function row_number does not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM p...
+               ^
+-- regular aggregate
+SELECT sum(orbit) OVER () FROM planets;
+  sum   
+--------
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+(10 rows)
+
+SELECT sum(orbit) RESPECT NULLS OVER () FROM planets; -- fails
+ERROR:  aggregate functions do not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT sum(orbit) RESPECT NULLS OVER () FROM planets;
+               ^
+SELECT sum(orbit) IGNORE NULLS OVER () FROM planets; -- fails
+ERROR:  aggregate functions do not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT sum(orbit) IGNORE NULLS OVER () FROM planets;
+               ^
+--cleanup
+DROP TABLE planets CASCADE;
+NOTICE:  drop cascades to view planets_view
diff --git a/src/test/regress/sql/create_function_3.sql b/src/test/regress/sql/create_function_3.sql
index bd108a918f..f7fe984e58 100644
--- a/src/test/regress/sql/create_function_3.sql
+++ b/src/test/regress/sql/create_function_3.sql
@@ -82,6 +82,12 @@ SELECT proname, prosecdef FROM pg_proc
                      'functest_C_2'::regproc,
                      'functest_C_3'::regproc) ORDER BY proname;
 
+--
+-- TREAT NULLS
+--
+CREATE FUNCTION functest_D_1(integer) RETURNS integer LANGUAGE 'sql'
+       TREAT NULLS AS 'SELECT $1';
+
 --
 -- LEAKPROOF
 --
@@ -190,6 +196,7 @@ DROP FUNCTION functest_b_2;  -- error, ambiguous
 
 CREATE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL AS 'SELECT $1';
 CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL WINDOW AS 'SELECT $1';
+CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL TREAT NULLS AS 'SELECT $1';
 CREATE OR REPLACE PROCEDURE functest1(a int) LANGUAGE SQL AS 'SELECT $1';
 DROP FUNCTION functest1(a int);
 
diff --git a/src/test/regress/sql/create_procedure.sql b/src/test/regress/sql/create_procedure.sql
index 2ef1c82cea..188f5f85a9 100644
--- a/src/test/regress/sql/create_procedure.sql
+++ b/src/test/regress/sql/create_procedure.sql
@@ -130,6 +130,7 @@ CALL version();  -- error: not a procedure
 CALL sum(1);  -- error: not a procedure
 
 CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
+CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 
 ALTER PROCEDURE ptest1(text) STRICT;
diff --git a/src/test/regress/sql/misc_sanity.sql b/src/test/regress/sql/misc_sanity.sql
index 3ce32e4725..ccb4f008d9 100644
--- a/src/test/regress/sql/misc_sanity.sql
+++ b/src/test/regress/sql/misc_sanity.sql
@@ -94,3 +94,12 @@ WHERE c.oid < 16384 AND
       relkind = 'r' AND
       attstorage != 'p'
 ORDER BY 1, 2;
+
+-- **************** pg_class ****************
+
+-- Look for non-window functions with null treatment (there should be none)
+
+SELECT proname, prokind, pronulltreatment
+FROM pg_proc
+WHERE pronulltreatment AND prokind <> 'w'
+ORDER BY oid;
diff --git a/src/test/regress/sql/window.sql b/src/test/regress/sql/window.sql
index eae5fa6017..a021ed3544 100644
--- a/src/test/regress/sql/window.sql
+++ b/src/test/regress/sql/window.sql
@@ -1328,3 +1328,104 @@ $$ LANGUAGE SQL STABLE;
 
 EXPLAIN (costs off) SELECT * FROM pg_temp.f(2);
 SELECT * FROM pg_temp.f(2);
+
+
+-- IGNORE NULLS tests
+
+CREATE TEMPORARY TABLE planets (
+    name text,
+    orbit integer
+);
+
+INSERT INTO planets VALUES
+  ('mercury', 88),
+  ('venus', 224),
+  ('earth', NULL),
+  ('mars', NULL),
+  ('jupiter', 4332),
+  ('saturn', 24491),
+  ('uranus', NULL),
+  ('neptune', 60182),
+  ('pluto', 90560),
+  ('xyzzy', NULL);
+
+-- test ruleutils
+CREATE VIEW planets_view AS
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+SELECT pg_get_viewdef('planets_view');
+
+-- lag
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+
+-- lead
+SELECT name,
+       orbit,
+       lead(orbit) OVER w AS lead,
+       lead(orbit) RESPECT NULLS OVER w AS lead_respect,
+       lead(orbit) IGNORE NULLS OVER w AS lead_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+
+-- first_value
+SELECT name,
+       orbit,
+       first_value(orbit) RESPECT NULLS OVER w1,
+       first_value(orbit) IGNORE NULLS OVER w1,
+       first_value(orbit) RESPECT NULLS OVER w2,
+       first_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- nth_value
+SELECT name,
+       orbit,
+       nth_value(orbit, 2) RESPECT NULLS OVER w1,
+       nth_value(orbit, 2) IGNORE NULLS OVER w1,
+       nth_value(orbit, 2) RESPECT NULLS OVER w2,
+       nth_value(orbit, 2) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- last_value
+SELECT name,
+       orbit,
+       last_value(orbit) RESPECT NULLS OVER w1,
+       last_value(orbit) IGNORE NULLS OVER w1,
+       last_value(orbit) RESPECT NULLS OVER w2,
+       last_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- window function without null treatment
+SELECT row_number() OVER (ORDER BY name) FROM planets;
+SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM planets; -- fails
+SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM planets; -- fails
+
+-- regular aggregate
+SELECT sum(orbit) OVER () FROM planets;
+SELECT sum(orbit) RESPECT NULLS OVER () FROM planets; -- fails
+SELECT sum(orbit) IGNORE NULLS OVER () FROM planets; -- fails
+
+--cleanup
+DROP TABLE planets CASCADE;

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 02a37658ad..7a6f194138 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -20402,6 +20402,14 @@ SELECT count(*) FROM sometable;
    about frame specifications.
   </para>
 
+  <para>
+   The functions <function>lead</function>, <function>lag</function>,
+   <function>first_value</function>, <function>last_value</function>, and
+   <function>nth_value</function> accept a null treatment option which is
+   <literal>RESPECT NULLS</literal> or <literal>IGNORE NULLS</literal>.
+   If this option is not specified, the default is <literal>RESPECT NULLS</literal>.
+  </para>
+
   <para>
    When an aggregate function is used as a window function, it aggregates
    over the rows within the current row's window frame.
@@ -20415,14 +20423,9 @@ SELECT count(*) FROM sometable;
 
   <note>
    <para>
-    The SQL standard defines a <literal>RESPECT NULLS</literal> or
-    <literal>IGNORE NULLS</literal> option for <function>lead</function>, <function>lag</function>,
-    <function>first_value</function>, <function>last_value</function>, and
-    <function>nth_value</function>.  This is not implemented in
-    <productname>PostgreSQL</productname>: the behavior is always the
-    same as the standard's default, namely <literal>RESPECT NULLS</literal>.
-    Likewise, the standard's <literal>FROM FIRST</literal> or <literal>FROM LAST</literal>
-    option for <function>nth_value</function> is not implemented: only the
+    The SQL standard defines a <literal>FROM FIRST</literal> or <literal>FROM LAST</literal>
+    option for <function>nth_value</function>.  This is not implemented in
+    <productname>PostgreSQL</productname>: only the
     default <literal>FROM FIRST</literal> behavior is supported.  (You can achieve
     the result of <literal>FROM LAST</literal> by reversing the <literal>ORDER BY</literal>
     ordering.)
diff --git a/doc/src/sgml/ref/create_function.sgml b/doc/src/sgml/ref/create_function.sgml
index 3c1eaea651..31e08c26b4 100644
--- a/doc/src/sgml/ref/create_function.sgml
+++ b/doc/src/sgml/ref/create_function.sgml
@@ -28,6 +28,7 @@ CREATE [ OR REPLACE ] FUNCTION
   { LANGUAGE <replaceable class="parameter">lang_name</replaceable>
     | TRANSFORM { FOR TYPE <replaceable class="parameter">type_name</replaceable> } [, ... ]
     | WINDOW
+    | TREAT NULLS
     | IMMUTABLE | STABLE | VOLATILE | [ NOT ] LEAKPROOF
     | CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
     | [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
@@ -293,6 +294,17 @@ CREATE [ OR REPLACE ] FUNCTION
      </listitem>
     </varlistentry>
 
+    <varlistentry>
+     <term><literal>TREAT NULLS</literal></term>
+
+     <listitem>
+      <para><literal>TREAT NULLS</literal> indicates that the function is able
+      to handle the <literal>RESPECT NULLS</literal> and <literal>IGNORE
+      NULLS</literal> options.  Only window functions may specify this.
+      </para>
+     </listitem>
+    </varlistentry>
+
     <varlistentry>
      <term><literal>IMMUTABLE</literal></term>
      <term><literal>STABLE</literal></term>
diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml
index d66560b587..103595d21b 100644
--- a/doc/src/sgml/syntax.sgml
+++ b/doc/src/sgml/syntax.sgml
@@ -1766,6 +1766,8 @@ FROM generate_series(1,10) AS s(i);
     The syntax of a window function call is one of the following:
 
 <synopsis>
+<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ RESPECT NULLS | IGNORE NULLS ] OVER <replaceable>window_name</replaceable>
+<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ RESPECT NULLS | IGNORE NULLS ] OVER ( <replaceable class="parameter">window_definition</replaceable> )
 <replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER <replaceable>window_name</replaceable>
 <replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER ( <replaceable class="parameter">window_definition</replaceable> )
 <replaceable>function_name</replaceable> ( * ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER <replaceable>window_name</replaceable>
@@ -1779,6 +1781,18 @@ FROM generate_series(1,10) AS s(i);
 [ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [ NULLS { FIRST | LAST } ] [, ...] ]
 [ <replaceable class="parameter">frame_clause</replaceable> ]
 </synopsis>
+   </para>
+
+   <note>
+    <para>
+     The versions with <literal>RESPECT NULLS</literal> or <literal>IGNORE
+     NULLS</literal> only apply to true window functions, whereas the versions
+     with <literal>FILTER</literal> only apply to aggregate functions used as
+     window functions.
+    </para>
+   </note>
+
+   <para>
     The optional <replaceable class="parameter">frame_clause</replaceable>
     can be one of
 <synopsis>
diff --git a/src/backend/catalog/pg_aggregate.c b/src/backend/catalog/pg_aggregate.c
index 89f23d0add..ff66f0e2cb 100644
--- a/src/backend/catalog/pg_aggregate.c
+++ b/src/backend/catalog/pg_aggregate.c
@@ -627,6 +627,7 @@ AggregateCreate(const char *aggName,
 									 * definable for agg) */
 							 false, /* isLeakProof */
 							 false, /* isStrict (not needed for agg) */
+							 false, /* null_treatment (not needed for agg) */
 							 PROVOLATILE_IMMUTABLE, /* volatility (not needed
 													 * for agg) */
 							 proparallel,
@@ -848,7 +849,7 @@ lookup_agg_function(List *fnName,
 							   nargs, input_types, false, false,
 							   &fnOid, rettype, &retset,
 							   &nvargs, &vatype,
-							   &true_oid_array, NULL);
+							   &true_oid_array, NULL, NULL);
 
 	/* only valid case is a normal function not returning a set */
 	if (fdresult != FUNCDETAIL_NORMAL || !OidIsValid(fnOid))
diff --git a/src/backend/catalog/pg_proc.c b/src/backend/catalog/pg_proc.c
index e14eee5a19..f07bfeccaa 100644
--- a/src/backend/catalog/pg_proc.c
+++ b/src/backend/catalog/pg_proc.c
@@ -80,6 +80,7 @@ ProcedureCreate(const char *procedureName,
 				bool security_definer,
 				bool isLeakProof,
 				bool isStrict,
+				bool null_treatment,
 				char volatility,
 				char parallel,
 				oidvector *parameterTypes,
@@ -307,6 +308,7 @@ ProcedureCreate(const char *procedureName,
 	values[Anum_pg_proc_prosecdef - 1] = BoolGetDatum(security_definer);
 	values[Anum_pg_proc_proleakproof - 1] = BoolGetDatum(isLeakProof);
 	values[Anum_pg_proc_proisstrict - 1] = BoolGetDatum(isStrict);
+	values[Anum_pg_proc_pronulltreatment - 1] = BoolGetDatum(null_treatment);
 	values[Anum_pg_proc_proretset - 1] = BoolGetDatum(returnsSet);
 	values[Anum_pg_proc_provolatile - 1] = CharGetDatum(volatility);
 	values[Anum_pg_proc_proparallel - 1] = CharGetDatum(parallel);
@@ -386,6 +388,12 @@ ProcedureCreate(const char *procedureName,
 					  errdetail("\"%s\" is a window function.", procedureName) :
 					  0)));
 
+		/* Not okay to set null treatment if not a window function */
+		if (null_treatment && oldproc->prokind != PROKIND_WINDOW)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+					 errmsg("cannot set null treatment on a non-window function")));
+
 		dropcmd = (prokind == PROKIND_PROCEDURE ? "DROP PROCEDURE" :
 				   prokind == PROKIND_AGGREGATE ? "DROP AGGREGATE" :
 				   "DROP FUNCTION");
diff --git a/src/backend/catalog/sql_features.txt b/src/backend/catalog/sql_features.txt
index caa971c435..0615b08858 100644
--- a/src/backend/catalog/sql_features.txt
+++ b/src/backend/catalog/sql_features.txt
@@ -508,9 +508,9 @@ T612	Advanced OLAP operations			YES
 T613	Sampling			YES	
 T614	NTILE function			YES	
 T615	LEAD and LAG functions			YES	
-T616	Null treatment option for LEAD and LAG functions			NO	
+T616	Null treatment option for LEAD and LAG functions			YES	
 T617	FIRST_VALUE and LAST_VALUE function			YES	
-T618	NTH_VALUE function			NO	function exists, but some options missing
+T618	NTH_VALUE function			NO	supported except FROM LAST is not implemented
 T619	Nested window functions			NO	
 T620	WINDOW clause: GROUPS option			YES	
 T621	Enhanced numeric functions			YES	
diff --git a/src/backend/commands/functioncmds.c b/src/backend/commands/functioncmds.c
index 7a4e104623..33c2f40015 100644
--- a/src/backend/commands/functioncmds.c
+++ b/src/backend/commands/functioncmds.c
@@ -697,6 +697,7 @@ compute_function_attributes(ParseState *pstate,
 							bool *windowfunc_p,
 							char *volatility_p,
 							bool *strict_p,
+							bool *null_treatment_p,
 							bool *security_definer,
 							bool *leakproof_p,
 							ArrayType **proconfig,
@@ -710,6 +711,7 @@ compute_function_attributes(ParseState *pstate,
 	DefElem    *language_item = NULL;
 	DefElem    *transform_item = NULL;
 	DefElem    *windowfunc_item = NULL;
+	DefElem    *nulltreatment_item = NULL;
 	DefElem    *volatility_item = NULL;
 	DefElem    *strict_item = NULL;
 	DefElem    *security_item = NULL;
@@ -765,6 +767,20 @@ compute_function_attributes(ParseState *pstate,
 						 parser_errposition(pstate, defel->location)));
 			windowfunc_item = defel;
 		}
+		else if (strcmp(defel->defname, "null_treatment") == 0)
+		{
+			if (nulltreatment_item)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options"),
+						 parser_errposition(pstate, defel->location)));
+			if (is_procedure)
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+						 errmsg("invalid attribute in procedure definition"),
+						 parser_errposition(pstate, defel->location)));
+			nulltreatment_item = defel;
+		}
 		else if (compute_common_attribute(pstate,
 										  is_procedure,
 										  defel,
@@ -816,6 +832,14 @@ compute_function_attributes(ParseState *pstate,
 		*volatility_p = interpret_func_volatility(volatility_item);
 	if (strict_item)
 		*strict_p = intVal(strict_item->arg);
+	if (nulltreatment_item)
+	{
+		*null_treatment_p = intVal(nulltreatment_item->arg);
+		if (*null_treatment_p && !*windowfunc_p)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+					 errmsg("cannot set null treatment on a non-window function")));
+	}
 	if (security_item)
 		*security_definer = intVal(security_item->arg);
 	if (leakproof_item)
@@ -941,6 +965,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 				isStrict,
 				security,
 				isLeakProof;
+	bool		null_treatment;
 	char		volatility;
 	ArrayType  *proconfig;
 	float4		procost;
@@ -964,6 +989,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 	/* Set default attributes */
 	isWindowFunc = false;
 	isStrict = false;
+	null_treatment = false;
 	security = false;
 	isLeakProof = false;
 	volatility = PROVOLATILE_VOLATILE;
@@ -979,7 +1005,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 								stmt->options,
 								&as_clause, &language, &transformDefElem,
 								&isWindowFunc, &volatility,
-								&isStrict, &security, &isLeakProof,
+								&isStrict, &null_treatment, &security, &isLeakProof,
 								&proconfig, &procost, &prorows,
 								&prosupport, &parallel);
 
@@ -1159,6 +1185,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 						   security,
 						   isLeakProof,
 						   isStrict,
+						   null_treatment,
 						   volatility,
 						   parallel,
 						   parameterTypes,
diff --git a/src/backend/commands/typecmds.c b/src/backend/commands/typecmds.c
index 76218fb47e..364b6de603 100644
--- a/src/backend/commands/typecmds.c
+++ b/src/backend/commands/typecmds.c
@@ -1779,6 +1779,7 @@ makeRangeConstructors(const char *name, Oid namespace,
 								 false, /* security_definer */
 								 false, /* leakproof */
 								 false, /* isStrict */
+								 false, /* null_treatment */
 								 PROVOLATILE_IMMUTABLE, /* volatility */
 								 PROPARALLEL_SAFE,	/* parallel safety */
 								 constructorArgTypesVector, /* parameterTypes */
@@ -1843,6 +1844,7 @@ makeMultirangeConstructors(const char *name, Oid namespace,
 							 false, /* security_definer */
 							 false, /* leakproof */
 							 false, /* isStrict */
+							 false, /* null_treatement */
 							 PROVOLATILE_IMMUTABLE, /* volatility */
 							 PROPARALLEL_SAFE,	/* parallel safety */
 							 argtypes,	/* parameterTypes */
@@ -1886,6 +1888,7 @@ makeMultirangeConstructors(const char *name, Oid namespace,
 							 false, /* security_definer */
 							 false, /* leakproof */
 							 true,	/* isStrict */
+							 false,	/* null_treatement */
 							 PROVOLATILE_IMMUTABLE, /* volatility */
 							 PROPARALLEL_SAFE,	/* parallel safety */
 							 argtypes,	/* parameterTypes */
@@ -1926,6 +1929,7 @@ makeMultirangeConstructors(const char *name, Oid namespace,
 							 false, /* security_definer */
 							 false, /* leakproof */
 							 false, /* isStrict */
+							 false, /* null_treatment */
 							 PROVOLATILE_IMMUTABLE, /* volatility */
 							 PROPARALLEL_SAFE,	/* parallel safety */
 							 argtypes,	/* parameterTypes */
diff --git a/src/backend/executor/nodeWindowAgg.c b/src/backend/executor/nodeWindowAgg.c
index f8ea9e96d8..f0aa8150a2 100644
--- a/src/backend/executor/nodeWindowAgg.c
+++ b/src/backend/executor/nodeWindowAgg.c
@@ -68,6 +68,7 @@ typedef struct WindowObjectData
 	int			readptr;		/* tuplestore read pointer for this fn */
 	int64		markpos;		/* row that markptr is positioned on */
 	int64		seekpos;		/* row that readptr is positioned on */
+	NullTreatment	null_treatment;	/* RESPECT/IGNORE NULLS? */
 } WindowObjectData;
 
 /*
@@ -2473,6 +2474,7 @@ ExecInitWindowAgg(WindowAgg *node, EState *estate, int eflags)
 			winobj->winstate = winstate;
 			winobj->argstates = wfuncstate->args;
 			winobj->localmem = NULL;
+			winobj->null_treatment = wfunc->winnulltreatment;
 			perfuncstate->winobj = winobj;
 
 			/* It's a real window function, so set up to call it. */
@@ -3173,48 +3175,103 @@ WinGetFuncArgInPartition(WindowObject winobj, int argno,
 	TupleTableSlot *slot;
 	bool		gottuple;
 	int64		abs_pos;
+	bool		ignore_nulls = false;
+	int			target = relpos;
+	int			step = 0;
+	Datum		result;
 
 	Assert(WindowObjectIsValid(winobj));
 	winstate = winobj->winstate;
 	econtext = winstate->ss.ps.ps_ExprContext;
 	slot = winstate->temp_slot_1;
 
-	switch (seektype)
+	/*
+	 * If we're not ignoring nulls, we'll just go straight to the desired row.
+	 * But if we are ignoring nulls, we'll have to step towards the target row
+	 * by row so we need to determine how we get there.
+	 */
+	if (winobj->null_treatment == NULL_TREATMENT_IGNORE)
 	{
-		case WINDOW_SEEK_CURRENT:
-			abs_pos = winstate->currentpos + relpos;
-			break;
-		case WINDOW_SEEK_HEAD:
-			abs_pos = relpos;
-			break;
-		case WINDOW_SEEK_TAIL:
-			spool_tuples(winstate, -1);
-			abs_pos = winstate->spooled_rows - 1 + relpos;
-			break;
-		default:
-			elog(ERROR, "unrecognized window seek type: %d", seektype);
-			abs_pos = 0;		/* keep compiler quiet */
-			break;
-	}
-
-	gottuple = window_gettupleslot(winobj, abs_pos, slot);
+		ignore_nulls = true;
 
-	if (!gottuple)
-	{
-		if (isout)
-			*isout = true;
-		*isnull = true;
-		return (Datum) 0;
+		if (seektype == WINDOW_SEEK_HEAD)
+		{
+			step = 1;
+			relpos = 0;
+		}
+		else if (seektype == WINDOW_SEEK_TAIL)
+		{
+			step = -1;
+			relpos = 0;
+		}
+		else
+		{
+			if (target > 0)
+				step = 1;
+			else if (target < 0)
+				step = -1;
+			else
+				step = 0;
+			relpos = step;
+		}
 	}
-	else
+
+	for (;;)
 	{
-		if (isout)
-			*isout = false;
-		if (set_mark)
-			WinSetMarkPosition(winobj, abs_pos);
+		switch (seektype)
+		{
+			case WINDOW_SEEK_CURRENT:
+				abs_pos = winstate->currentpos + relpos;
+				break;
+			case WINDOW_SEEK_HEAD:
+				abs_pos = relpos;
+				break;
+			case WINDOW_SEEK_TAIL:
+				spool_tuples(winstate, -1);
+				abs_pos = winstate->spooled_rows - 1 + relpos;
+				break;
+			default:
+				elog(ERROR, "unrecognized window seek type: %d", seektype);
+				abs_pos = 0;		/* keep compiler quiet */
+				break;
+		}
+
+		gottuple = window_gettupleslot(winobj, abs_pos, slot);
+
+		/* Did we fall off the end of the partition? */
+		if (!gottuple)
+		{
+			if (isout)
+				*isout = true;
+			*isnull = true;
+			return (Datum) 0;
+		}
+
+		/* Evaluate the expression at this row */
 		econtext->ecxt_outertuple = slot;
-		return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
-							econtext, isnull);
+		result = ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
+							  econtext, isnull);
+
+		/* If we got a null and we're ignoring them, move the goalposts */
+		if (ignore_nulls && *isnull)
+			target += step;
+
+		/* Once we've reached our target, we're done */
+		if (relpos == target)
+		{
+			if (isout)
+				*isout = false;
+			/*
+			 * We can only mark the row if we're not ignoring nulls (because we
+			 * jump straight there).
+			 */
+			if (set_mark && !ignore_nulls)
+				WinSetMarkPosition(winobj, abs_pos);
+			return result;
+		}
+
+		/* Otherwise move closer and try again */
+		relpos += step;
 	}
 }
 
@@ -3261,170 +3318,218 @@ WinGetFuncArgInFrame(WindowObject winobj, int argno,
 	TupleTableSlot *slot;
 	int64		abs_pos;
 	int64		mark_pos;
+	bool		ignore_nulls = false;
+	int			target = relpos;
+	int			step = 0;
+	Datum		result;
 
 	Assert(WindowObjectIsValid(winobj));
 	winstate = winobj->winstate;
 	econtext = winstate->ss.ps.ps_ExprContext;
 	slot = winstate->temp_slot_1;
 
-	switch (seektype)
+	/*
+	 * If we're not ignoring nulls, we'll just go straight to the desired row.
+	 * But if we are ignoring nulls, we'll have to step towards the target row
+	 * by row so we need to determine how we get there.
+	 */
+	if (winobj->null_treatment == NULL_TREATMENT_IGNORE)
 	{
-		case WINDOW_SEEK_CURRENT:
-			elog(ERROR, "WINDOW_SEEK_CURRENT is not supported for WinGetFuncArgInFrame");
-			abs_pos = mark_pos = 0; /* keep compiler quiet */
-			break;
-		case WINDOW_SEEK_HEAD:
-			/* rejecting relpos < 0 is easy and simplifies code below */
-			if (relpos < 0)
-				goto out_of_frame;
-			update_frameheadpos(winstate);
-			abs_pos = winstate->frameheadpos + relpos;
-			mark_pos = abs_pos;
+		ignore_nulls = true;
 
-			/*
-			 * Account for exclusion option if one is active, but advance only
-			 * abs_pos not mark_pos.  This prevents changes of the current
-			 * row's peer group from resulting in trying to fetch a row before
-			 * some previous mark position.
-			 *
-			 * Note that in some corner cases such as current row being
-			 * outside frame, these calculations are theoretically too simple,
-			 * but it doesn't matter because we'll end up deciding the row is
-			 * out of frame.  We do not attempt to avoid fetching rows past
-			 * end of frame; that would happen in some cases anyway.
-			 */
-			switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
-			{
-				case 0:
-					/* no adjustment needed */
-					break;
-				case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
-					if (abs_pos >= winstate->currentpos &&
-						winstate->currentpos >= winstate->frameheadpos)
-						abs_pos++;
-					break;
-				case FRAMEOPTION_EXCLUDE_GROUP:
-					update_grouptailpos(winstate);
-					if (abs_pos >= winstate->groupheadpos &&
-						winstate->grouptailpos > winstate->frameheadpos)
-					{
-						int64		overlapstart = Max(winstate->groupheadpos,
-													   winstate->frameheadpos);
+		if (target > 0)
+			step = 1;
+		else if (target < 0)
+			step = -1;
+		else if (seektype == WINDOW_SEEK_HEAD)
+			step = 1;
+		else if (seektype == WINDOW_SEEK_TAIL)
+			step = -1;
+		else
+			step = 0;
 
-						abs_pos += winstate->grouptailpos - overlapstart;
-					}
-					break;
-				case FRAMEOPTION_EXCLUDE_TIES:
-					update_grouptailpos(winstate);
-					if (abs_pos >= winstate->groupheadpos &&
-						winstate->grouptailpos > winstate->frameheadpos)
-					{
-						int64		overlapstart = Max(winstate->groupheadpos,
-													   winstate->frameheadpos);
+		relpos = 0;
+	}
 
-						if (abs_pos == overlapstart)
-							abs_pos = winstate->currentpos;
-						else
-							abs_pos += winstate->grouptailpos - overlapstart - 1;
-					}
-					break;
-				default:
-					elog(ERROR, "unrecognized frame option state: 0x%x",
-						 winstate->frameOptions);
-					break;
-			}
-			break;
-		case WINDOW_SEEK_TAIL:
-			/* rejecting relpos > 0 is easy and simplifies code below */
-			if (relpos > 0)
-				goto out_of_frame;
-			update_frametailpos(winstate);
-			abs_pos = winstate->frametailpos - 1 + relpos;
+	for (;;)
+	{
+		switch (seektype)
+		{
+			case WINDOW_SEEK_CURRENT:
+				elog(ERROR, "WINDOW_SEEK_CURRENT is not supported for WinGetFuncArgInFrame");
+				abs_pos = mark_pos = 0; /* keep compiler quiet */
+				break;
+			case WINDOW_SEEK_HEAD:
+				/* rejecting relpos < 0 is easy and simplifies code below */
+				if (relpos < 0)
+					goto out_of_frame;
+				update_frameheadpos(winstate);
+				abs_pos = winstate->frameheadpos + relpos;
+				mark_pos = abs_pos;
 
-			/*
-			 * Account for exclusion option if one is active.  If there is no
-			 * exclusion, we can safely set the mark at the accessed row.  But
-			 * if there is, we can only mark the frame start, because we can't
-			 * be sure how far back in the frame the exclusion might cause us
-			 * to fetch in future.  Furthermore, we have to actually check
-			 * against frameheadpos here, since it's unsafe to try to fetch a
-			 * row before frame start if the mark might be there already.
-			 */
-			switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
-			{
-				case 0:
-					/* no adjustment needed */
-					mark_pos = abs_pos;
-					break;
-				case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
-					if (abs_pos <= winstate->currentpos &&
-						winstate->currentpos < winstate->frametailpos)
-						abs_pos--;
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				case FRAMEOPTION_EXCLUDE_GROUP:
-					update_grouptailpos(winstate);
-					if (abs_pos < winstate->grouptailpos &&
-						winstate->groupheadpos < winstate->frametailpos)
-					{
-						int64		overlapend = Min(winstate->grouptailpos,
-													 winstate->frametailpos);
+				/*
+				 * Account for exclusion option if one is active, but advance only
+				 * abs_pos not mark_pos.  This prevents changes of the current
+				 * row's peer group from resulting in trying to fetch a row before
+				 * some previous mark position.
+				 *
+				 * Note that in some corner cases such as current row being
+				 * outside frame, these calculations are theoretically too simple,
+				 * but it doesn't matter because we'll end up deciding the row is
+				 * out of frame.  We do not attempt to avoid fetching rows past
+				 * end of frame; that would happen in some cases anyway.
+				 */
+				switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
+				{
+					case 0:
+						/* no adjustment needed */
+						break;
+					case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
+						if (abs_pos >= winstate->currentpos &&
+							winstate->currentpos >= winstate->frameheadpos)
+							abs_pos++;
+						break;
+					case FRAMEOPTION_EXCLUDE_GROUP:
+						update_grouptailpos(winstate);
+						if (abs_pos >= winstate->groupheadpos &&
+							winstate->grouptailpos > winstate->frameheadpos)
+						{
+							int64		overlapstart = Max(winstate->groupheadpos,
+														   winstate->frameheadpos);
+
+							abs_pos += winstate->grouptailpos - overlapstart;
+						}
+						break;
+					case FRAMEOPTION_EXCLUDE_TIES:
+						update_grouptailpos(winstate);
+						if (abs_pos >= winstate->groupheadpos &&
+							winstate->grouptailpos > winstate->frameheadpos)
+						{
+							int64		overlapstart = Max(winstate->groupheadpos,
+														   winstate->frameheadpos);
+
+							if (abs_pos == overlapstart)
+								abs_pos = winstate->currentpos;
+							else
+								abs_pos += winstate->grouptailpos - overlapstart - 1;
+						}
+						break;
+					default:
+						elog(ERROR, "unrecognized frame option state: 0x%x",
+							 winstate->frameOptions);
+						break;
+				}
+				break;
+			case WINDOW_SEEK_TAIL:
+				/* rejecting relpos > 0 is easy and simplifies code below */
+				if (relpos > 0)
+					goto out_of_frame;
+				update_frametailpos(winstate);
+				abs_pos = winstate->frametailpos - 1 + relpos;
 
-						abs_pos -= overlapend - winstate->groupheadpos;
-					}
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				case FRAMEOPTION_EXCLUDE_TIES:
-					update_grouptailpos(winstate);
-					if (abs_pos < winstate->grouptailpos &&
-						winstate->groupheadpos < winstate->frametailpos)
-					{
-						int64		overlapend = Min(winstate->grouptailpos,
-													 winstate->frametailpos);
+				/*
+				 * Account for exclusion option if one is active.  If there is no
+				 * exclusion, we can safely set the mark at the accessed row.  But
+				 * if there is, we can only mark the frame start, because we can't
+				 * be sure how far back in the frame the exclusion might cause us
+				 * to fetch in future.  Furthermore, we have to actually check
+				 * against frameheadpos here, since it's unsafe to try to fetch a
+				 * row before frame start if the mark might be there already.
+				 */
+				switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
+				{
+					case 0:
+						/* no adjustment needed */
+						mark_pos = abs_pos;
+						break;
+					case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
+						if (abs_pos <= winstate->currentpos &&
+							winstate->currentpos < winstate->frametailpos)
+							abs_pos--;
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					case FRAMEOPTION_EXCLUDE_GROUP:
+						update_grouptailpos(winstate);
+						if (abs_pos < winstate->grouptailpos &&
+							winstate->groupheadpos < winstate->frametailpos)
+						{
+							int64		overlapend = Min(winstate->grouptailpos,
+														 winstate->frametailpos);
+
+							abs_pos -= overlapend - winstate->groupheadpos;
+						}
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					case FRAMEOPTION_EXCLUDE_TIES:
+						update_grouptailpos(winstate);
+						if (abs_pos < winstate->grouptailpos &&
+							winstate->groupheadpos < winstate->frametailpos)
+						{
+							int64		overlapend = Min(winstate->grouptailpos,
+														 winstate->frametailpos);
+
+							if (abs_pos == overlapend - 1)
+								abs_pos = winstate->currentpos;
+							else
+								abs_pos -= overlapend - 1 - winstate->groupheadpos;
+						}
+						update_frameheadpos(winstate);
+						if (abs_pos < winstate->frameheadpos)
+							goto out_of_frame;
+						mark_pos = winstate->frameheadpos;
+						break;
+					default:
+						elog(ERROR, "unrecognized frame option state: 0x%x",
+							 winstate->frameOptions);
+						mark_pos = 0;	/* keep compiler quiet */
+						break;
+				}
+				break;
+			default:
+				elog(ERROR, "unrecognized window seek type: %d", seektype);
+				abs_pos = mark_pos = 0; /* keep compiler quiet */
+				break;
+		}
 
-						if (abs_pos == overlapend - 1)
-							abs_pos = winstate->currentpos;
-						else
-							abs_pos -= overlapend - 1 - winstate->groupheadpos;
-					}
-					update_frameheadpos(winstate);
-					if (abs_pos < winstate->frameheadpos)
-						goto out_of_frame;
-					mark_pos = winstate->frameheadpos;
-					break;
-				default:
-					elog(ERROR, "unrecognized frame option state: 0x%x",
-						 winstate->frameOptions);
-					mark_pos = 0;	/* keep compiler quiet */
-					break;
-			}
-			break;
-		default:
-			elog(ERROR, "unrecognized window seek type: %d", seektype);
-			abs_pos = mark_pos = 0; /* keep compiler quiet */
-			break;
-	}
+		if (!window_gettupleslot(winobj, abs_pos, slot))
+			goto out_of_frame;
 
-	if (!window_gettupleslot(winobj, abs_pos, slot))
-		goto out_of_frame;
+		/* The code above does not detect all out-of-frame cases, so check */
+		if (row_is_in_frame(winstate, abs_pos, slot) <= 0)
+			goto out_of_frame;
 
-	/* The code above does not detect all out-of-frame cases, so check */
-	if (row_is_in_frame(winstate, abs_pos, slot) <= 0)
-		goto out_of_frame;
+		/* Evaluate the expression at this row */
+		econtext->ecxt_outertuple = slot;
+		result = ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
+							  econtext, isnull);
 
-	if (isout)
-		*isout = false;
-	if (set_mark)
-		WinSetMarkPosition(winobj, mark_pos);
-	econtext->ecxt_outertuple = slot;
-	return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
-						econtext, isnull);
+		/* If we got a null and we're ignoring them, move the goalposts */
+		if (ignore_nulls && *isnull)
+			target += step;
+
+		/* Once we've reached our target, we're done */
+		if (relpos == target)
+		{
+			if (isout)
+				*isout = false;
+			/*
+			 * We can only mark the row if we're not ignoring nulls (because we
+			 * jump straight there).
+			 */
+			if (set_mark && !ignore_nulls)
+				WinSetMarkPosition(winobj, mark_pos);
+			return result;
+		}
+
+		/* Otherwise move closer and try again */
+		relpos += step;
+	}
 
 out_of_frame:
 	if (isout)
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index ba3ccc712c..afc0094ca8 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -1533,6 +1533,7 @@ _copyWindowFunc(const WindowFunc *from)
 	COPY_SCALAR_FIELD(winref);
 	COPY_SCALAR_FIELD(winstar);
 	COPY_SCALAR_FIELD(winagg);
+	COPY_SCALAR_FIELD(winnulltreatment);
 	COPY_LOCATION_FIELD(location);
 
 	return newnode;
@@ -2691,6 +2692,7 @@ _copyFuncCall(const FuncCall *from)
 	COPY_SCALAR_FIELD(agg_distinct);
 	COPY_SCALAR_FIELD(func_variadic);
 	COPY_SCALAR_FIELD(funcformat);
+	COPY_SCALAR_FIELD(win_null_treatment);
 	COPY_LOCATION_FIELD(location);
 
 	return newnode;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index a2ef853dc2..c2fd7967c5 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -266,6 +266,7 @@ _equalWindowFunc(const WindowFunc *a, const WindowFunc *b)
 	COMPARE_SCALAR_FIELD(winref);
 	COMPARE_SCALAR_FIELD(winstar);
 	COMPARE_SCALAR_FIELD(winagg);
+	COMPARE_SCALAR_FIELD(winnulltreatment);
 	COMPARE_LOCATION_FIELD(location);
 
 	return true;
@@ -2392,6 +2393,7 @@ _equalFuncCall(const FuncCall *a, const FuncCall *b)
 	COMPARE_SCALAR_FIELD(agg_distinct);
 	COMPARE_SCALAR_FIELD(func_variadic);
 	COMPARE_SCALAR_FIELD(funcformat);
+	COMPARE_SCALAR_FIELD(win_null_treatment);
 	COMPARE_LOCATION_FIELD(location);
 
 	return true;
diff --git a/src/backend/nodes/makefuncs.c b/src/backend/nodes/makefuncs.c
index 01c110cd2f..5b158b0d09 100644
--- a/src/backend/nodes/makefuncs.c
+++ b/src/backend/nodes/makefuncs.c
@@ -596,6 +596,7 @@ makeFuncCall(List *name, List *args, CoercionForm funcformat, int location)
 	n->agg_distinct = false;
 	n->func_variadic = false;
 	n->funcformat = funcformat;
+	n->win_null_treatment = NULL_TREATMENT_NONE;
 	n->location = location;
 	return n;
 }
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 8392be6d44..0dbb35fba7 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -1184,6 +1184,7 @@ _outWindowFunc(StringInfo str, const WindowFunc *node)
 	WRITE_UINT_FIELD(winref);
 	WRITE_BOOL_FIELD(winstar);
 	WRITE_BOOL_FIELD(winagg);
+	WRITE_INT_FIELD(winnulltreatment);
 	WRITE_LOCATION_FIELD(location);
 }
 
@@ -2802,6 +2803,7 @@ _outFuncCall(StringInfo str, const FuncCall *node)
 	WRITE_BOOL_FIELD(agg_distinct);
 	WRITE_BOOL_FIELD(func_variadic);
 	WRITE_ENUM_FIELD(funcformat, CoercionForm);
+	WRITE_BOOL_FIELD(win_null_treatment);
 	WRITE_LOCATION_FIELD(location);
 }
 
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index d2c8d58070..de6a965f46 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -656,6 +656,7 @@ _readWindowFunc(void)
 	READ_UINT_FIELD(winref);
 	READ_BOOL_FIELD(winstar);
 	READ_BOOL_FIELD(winagg);
+	READ_INT_FIELD(winnulltreatment);
 	READ_LOCATION_FIELD(location);
 
 	READ_DONE();
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 51d26a0691..931231a1f1 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -2221,6 +2221,7 @@ eval_const_expressions_mutator(Node *node,
 				newexpr->winref = expr->winref;
 				newexpr->winstar = expr->winstar;
 				newexpr->winagg = expr->winagg;
+				newexpr->winnulltreatment = expr->winnulltreatment;
 				newexpr->location = expr->location;
 
 				return (Node *) newexpr;
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 31c95443a5..40f4e549aa 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -583,6 +583,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <list>	window_clause window_definition_list opt_partition_clause
 %type <windef>	window_definition over_clause window_specification
 				opt_frame_clause frame_extent frame_bound
+%type <ival>	null_treatment
 %type <ival>	opt_window_exclusion_clause
 %type <str>		opt_existing_window_name
 %type <boolean> opt_if_not_exists
@@ -651,7 +652,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 	HANDLER HAVING HEADER_P HOLD HOUR_P
 
-	IDENTITY_P IF_P ILIKE IMMEDIATE IMMUTABLE IMPLICIT_P IMPORT_P IN_P INCLUDE
+	IDENTITY_P IF_P IGNORE_P ILIKE IMMEDIATE IMMUTABLE IMPLICIT_P IMPORT_P IN_P INCLUDE
 	INCLUDING INCREMENT INDEX INDEXES INHERIT INHERITS INITIALLY INLINE_P
 	INNER_P INOUT INPUT_P INSENSITIVE INSERT INSTEAD INT_P INTEGER
 	INTERSECT INTERVAL INTO INVOKER IS ISNULL ISOLATION
@@ -683,7 +684,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 	RANGE READ REAL REASSIGN RECHECK RECURSIVE REF REFERENCES REFERENCING
 	REFRESH REINDEX RELATIVE_P RELEASE RENAME REPEATABLE REPLACE REPLICA
-	RESET RESTART RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROLLUP
+	RESET RESPECT RESTART RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROLLUP
 	ROUTINE ROUTINES ROW ROWS RULE
 
 	SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
@@ -7848,6 +7849,10 @@ createfunc_opt_item:
 				{
 					$$ = makeDefElem("window", (Node *)makeInteger(true), @1);
 				}
+			| TREAT NULLS_P
+				{
+					$$ = makeDefElem("null_treatment", (Node *)makeInteger(true), @1);
+				}
 			| common_func_opt_item
 				{
 					$$ = $1;
@@ -13725,6 +13730,14 @@ func_expr: func_application within_group_clause filter_clause over_clause
 					}
 					n->agg_filter = $3;
 					n->over = $4;
+					n->win_null_treatment = NULL_TREATMENT_NONE;
+					$$ = (Node *) n;
+				}
+			| func_application null_treatment over_clause
+				{
+					FuncCall *n = (FuncCall *) $1;
+					n->over = $3;
+					n->win_null_treatment = $2;
 					$$ = (Node *) n;
 				}
 			| func_expr_common_subexpr
@@ -14145,6 +14158,11 @@ window_definition:
 				}
 		;
 
+null_treatment:
+			IGNORE_P NULLS_P	{ $$ = NULL_TREATMENT_IGNORE; }
+			| RESPECT NULLS_P	{ $$ = NULL_TREATMENT_RESPECT; }
+		;
+
 over_clause: OVER window_specification
 				{ $$ = $2; }
 			| OVER ColId
@@ -15292,6 +15310,7 @@ unreserved_keyword:
 			| HOUR_P
 			| IDENTITY_P
 			| IF_P
+			| IGNORE_P
 			| IMMEDIATE
 			| IMMUTABLE
 			| IMPLICIT_P
@@ -15398,6 +15417,7 @@ unreserved_keyword:
 			| REPLACE
 			| REPLICA
 			| RESET
+			| RESPECT
 			| RESTART
 			| RESTRICT
 			| RETURNS
diff --git a/src/backend/parser/parse_func.c b/src/backend/parser/parse_func.c
index 07d0013e84..ee2e7eceae 100644
--- a/src/backend/parser/parse_func.c
+++ b/src/backend/parser/parse_func.c
@@ -97,6 +97,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 	bool		agg_distinct = (fn ? fn->agg_distinct : false);
 	bool		func_variadic = (fn ? fn->func_variadic : false);
 	CoercionForm funcformat = (fn ? fn->funcformat : COERCE_EXPLICIT_CALL);
+	NullTreatment	win_null_treatment = (fn ? fn->win_null_treatment : NULL_TREATMENT_NONE);
 	bool		could_be_projection;
 	Oid			rettype;
 	Oid			funcid;
@@ -108,6 +109,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 	Oid		   *declared_arg_types;
 	List	   *argnames;
 	List	   *argdefaults;
+	bool		null_treatment;
 	Node	   *retval;
 	bool		retset;
 	int			nvargs;
@@ -267,7 +269,8 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 							   !func_variadic, true,
 							   &funcid, &rettype, &retset,
 							   &nvargs, &vatype,
-							   &declared_arg_types, &argdefaults);
+							   &declared_arg_types, &argdefaults,
+							   &null_treatment);
 
 	cancel_parser_errposition_callback(&pcbstate);
 
@@ -507,6 +510,13 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 						 errmsg("%s is not an ordered-set aggregate, so it cannot have WITHIN GROUP",
 								NameListToString(funcname)),
 						 parser_errposition(pstate, location)));
+
+			/* It also can't treat nulls as a window function */
+			if (over && win_null_treatment != NULL_TREATMENT_NONE)
+				ereport(ERROR,
+						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+						 errmsg("aggregate functions do not accept RESPECT/IGNORE NULLS"),
+						 parser_errposition(pstate, location)));
 		}
 	}
 	else if (fdresult == FUNCDETAIL_WINDOWFUNC)
@@ -527,6 +537,13 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 					 errmsg("window function %s cannot have WITHIN GROUP",
 							NameListToString(funcname)),
 					 parser_errposition(pstate, location)));
+
+		if (!null_treatment && win_null_treatment != NULL_TREATMENT_NONE)
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("window function %s does not accept RESPECT/IGNORE NULLS",
+							NameListToString(funcname)),
+					 parser_errposition(pstate, location)));
 	}
 	else if (fdresult == FUNCDETAIL_COERCION)
 	{
@@ -826,6 +843,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 		wfunc->winstar = agg_star;
 		wfunc->winagg = (fdresult == FUNCDETAIL_AGGREGATE);
 		wfunc->aggfilter = agg_filter;
+		wfunc->winnulltreatment = win_null_treatment;
 		wfunc->location = location;
 
 		/*
@@ -1396,7 +1414,8 @@ func_get_detail(List *funcname,
 				int *nvargs,	/* return value */
 				Oid *vatype,	/* return value */
 				Oid **true_typeids, /* return value */
-				List **argdefaults) /* optional return value */
+				List **argdefaults, /* optional return value */
+				bool *null_treatment) /* optional return value */
 {
 	FuncCandidateList raw_candidates;
 	FuncCandidateList best_candidate;
@@ -1410,6 +1429,8 @@ func_get_detail(List *funcname,
 	*true_typeids = NULL;
 	if (argdefaults)
 		*argdefaults = NIL;
+	if (null_treatment)
+		*null_treatment = NULL_TREATMENT_NONE;
 
 	/* Get list of possible candidates from namespace search */
 	raw_candidates = FuncnameGetCandidates(funcname, nargs, fargnames,
@@ -1687,6 +1708,8 @@ func_get_detail(List *funcname,
 				*argdefaults = defaults;
 			}
 		}
+		if (null_treatment)
+			*null_treatment = pform->pronulltreatment;
 
 		switch (pform->prokind)
 		{
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index db803b4388..aa31fb0cfb 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -2660,6 +2660,9 @@ pg_get_functiondef(PG_FUNCTION_ARGS)
 
 	if (proc->prokind == PROKIND_WINDOW)
 		appendStringInfoString(&buf, " WINDOW");
+	if (proc->pronulltreatment)
+		appendStringInfoString(&buf, " TREAT NULLS");
+
 	switch (proc->provolatile)
 	{
 		case PROVOLATILE_IMMUTABLE:
@@ -9474,7 +9477,12 @@ get_windowfunc_expr(WindowFunc *wfunc, deparse_context *context)
 		get_rule_expr((Node *) wfunc->aggfilter, context, false);
 	}
 
-	appendStringInfoString(buf, ") OVER ");
+	if (wfunc->winnulltreatment == NULL_TREATMENT_IGNORE)
+		appendStringInfoString(buf, ") IGNORE NULLS OVER ");
+	else if (wfunc->winnulltreatment == NULL_TREATMENT_RESPECT)
+		appendStringInfoString(buf, ") RESPECT NULLS OVER ");
+	else
+		appendStringInfoString(buf, ") OVER ");
 
 	foreach(l, context->windowClause)
 	{
@@ -11227,7 +11235,7 @@ generate_function_name(Oid funcid, int nargs, List *argnames, Oid *argtypes,
 								   !use_variadic, true,
 								   &p_funcid, &p_rettype,
 								   &p_retset, &p_nvargs, &p_vatype,
-								   &p_true_typeids, NULL);
+								   &p_true_typeids, NULL, NULL);
 	else
 	{
 		p_result = FUNCDETAIL_NOTFOUND;
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index d7b55f57ea..77345a4b89 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -9770,33 +9770,42 @@
   proargtypes => 'int4', prosrc => 'window_ntile' },
 { oid => '3106', descr => 'fetch the preceding row value',
   proname => 'lag', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_lag' },
+  proargtypes => 'anyelement', prosrc => 'window_lag',
+  pronulltreatment => 't' },
 { oid => '3107', descr => 'fetch the Nth preceding row value',
   proname => 'lag', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_lag_with_offset' },
+  proargtypes => 'anyelement int4', prosrc => 'window_lag_with_offset',
+  pronulltreatment => 't' },
 { oid => '3108', descr => 'fetch the Nth preceding row value with default',
   proname => 'lag', prokind => 'w', prorettype => 'anycompatible',
   proargtypes => 'anycompatible int4 anycompatible',
-  prosrc => 'window_lag_with_offset_and_default' },
+  prosrc => 'window_lag_with_offset_and_default',
+  pronulltreatment => 't' },
 { oid => '3109', descr => 'fetch the following row value',
   proname => 'lead', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_lead' },
+  proargtypes => 'anyelement', prosrc => 'window_lead',
+  pronulltreatment => 't' },
 { oid => '3110', descr => 'fetch the Nth following row value',
   proname => 'lead', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_lead_with_offset' },
+  proargtypes => 'anyelement int4', prosrc => 'window_lead_with_offset',
+  pronulltreatment => 't' },
 { oid => '3111', descr => 'fetch the Nth following row value with default',
   proname => 'lead', prokind => 'w', prorettype => 'anycompatible',
   proargtypes => 'anycompatible int4 anycompatible',
-  prosrc => 'window_lead_with_offset_and_default' },
+  prosrc => 'window_lead_with_offset_and_default',
+  pronulltreatment => 't' },
 { oid => '3112', descr => 'fetch the first row value',
   proname => 'first_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_first_value' },
+  proargtypes => 'anyelement', prosrc => 'window_first_value',
+  pronulltreatment => 't' },
 { oid => '3113', descr => 'fetch the last row value',
   proname => 'last_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement', prosrc => 'window_last_value' },
+  proargtypes => 'anyelement', prosrc => 'window_last_value',
+  pronulltreatment => 't' },
 { oid => '3114', descr => 'fetch the Nth row value',
   proname => 'nth_value', prokind => 'w', prorettype => 'anyelement',
-  proargtypes => 'anyelement int4', prosrc => 'window_nth_value' },
+  proargtypes => 'anyelement int4', prosrc => 'window_nth_value',
+  pronulltreatment => 't' },
 
 # functions for range types
 { oid => '3832', descr => 'I/O',
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index 1c2551c932..4f05db91ff 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -67,6 +67,9 @@ CATALOG(pg_proc,1255,ProcedureRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(81,Proce
 	/* strict with respect to NULLs? */
 	bool		proisstrict BKI_DEFAULT(t);
 
+	/* can handle IGNORE/RESPECT NULLS? (must be window function) */
+	bool		pronulltreatment BKI_DEFAULT(f);
+
 	/* returns a set? */
 	bool		proretset BKI_DEFAULT(f);
 
@@ -198,6 +201,7 @@ extern ObjectAddress ProcedureCreate(const char *procedureName,
 									 bool security_definer,
 									 bool isLeakProof,
 									 bool isStrict,
+									 bool null_treatment,
 									 char volatility,
 									 char parallel,
 									 oidvector *parameterTypes,
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index dc2bb40926..1cad850c26 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -357,6 +357,7 @@ typedef struct FuncCall
 	bool		agg_distinct;	/* arguments were labeled DISTINCT */
 	bool		func_variadic;	/* last argument was labeled VARIADIC */
 	CoercionForm funcformat;	/* how to display this node */
+	NullTreatment	win_null_treatment;	/* IGNORE NULLS or RESPECT NULLS? */
 	int			location;		/* token location, or -1 if unknown */
 } FuncCall;
 
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index d4ce037088..a7e4c1ee78 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -52,6 +52,13 @@ typedef enum OnCommitAction
 	ONCOMMIT_DROP				/* ON COMMIT DROP */
 } OnCommitAction;
 
+typedef enum NullTreatment
+{
+	NULL_TREATMENT_NONE = 0,
+	NULL_TREATMENT_RESPECT,
+	NULL_TREATMENT_IGNORE
+} NullTreatment;
+
 /*
  * RangeVar - range variable, used in FROM clauses
  *
@@ -387,6 +394,7 @@ typedef struct WindowFunc
 	Index		winref;			/* index of associated WindowClause */
 	bool		winstar;		/* true if argument list was really '*' */
 	bool		winagg;			/* is function a simple aggregate? */
+	NullTreatment	winnulltreatment;	/* can accept RESPECT/IGNORE NULLS? */
 	int			location;		/* token location, or -1 if unknown */
 } WindowFunc;
 
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 8c554e1f69..e8c902b81f 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -190,6 +190,7 @@ PG_KEYWORD("hold", HOLD, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("hour", HOUR_P, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("identity", IDENTITY_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("if", IF_P, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("ignore", IGNORE_P, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("ilike", ILIKE, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("immediate", IMMEDIATE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("immutable", IMMUTABLE, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -342,6 +343,7 @@ PG_KEYWORD("repeatable", REPEATABLE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("replace", REPLACE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("replica", REPLICA, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("reset", RESET, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("respect", RESPECT, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("restart", RESTART, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("restrict", RESTRICT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("returning", RETURNING, RESERVED_KEYWORD, AS_LABEL)
diff --git a/src/include/parser/parse_func.h b/src/include/parser/parse_func.h
index aaf07f8f73..c4704695ce 100644
--- a/src/include/parser/parse_func.h
+++ b/src/include/parser/parse_func.h
@@ -41,7 +41,8 @@ extern FuncDetailCode func_get_detail(List *funcname,
 									  bool expand_variadic, bool expand_defaults,
 									  Oid *funcid, Oid *rettype,
 									  bool *retset, int *nvargs, Oid *vatype,
-									  Oid **true_typeids, List **argdefaults);
+									  Oid **true_typeids, List **argdefaults,
+									  bool *null_treatment);
 
 extern int	func_match_argtypes(int nargs,
 								Oid *input_typeids,
diff --git a/src/test/regress/expected/create_function_3.out b/src/test/regress/expected/create_function_3.out
index ce508ae1dc..0311f8ecc9 100644
--- a/src/test/regress/expected/create_function_3.out
+++ b/src/test/regress/expected/create_function_3.out
@@ -122,6 +122,12 @@ SELECT proname, prosecdef FROM pg_proc
  functest_c_3 | t
 (3 rows)
 
+--
+-- TREAT NULLS
+--
+CREATE FUNCTION functest_D_1(integer) RETURNS integer LANGUAGE 'sql'
+       TREAT NULLS AS 'SELECT $1';
+ERROR:  cannot set null treatment on a non-window function
 --
 -- LEAKPROOF
 --
@@ -298,6 +304,8 @@ CREATE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL AS 'SELECT $1';
 CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL WINDOW AS 'SELECT $1';
 ERROR:  cannot change routine kind
 DETAIL:  "functest1" is a function.
+CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL TREAT NULLS AS 'SELECT $1';
+ERROR:  cannot set null treatment on a non-window function
 CREATE OR REPLACE PROCEDURE functest1(a int) LANGUAGE SQL AS 'SELECT $1';
 ERROR:  cannot change routine kind
 DETAIL:  "functest1" is a function.
diff --git a/src/test/regress/expected/create_procedure.out b/src/test/regress/expected/create_procedure.out
index 3838fa2324..f81f9b79cc 100644
--- a/src/test/regress/expected/create_procedure.out
+++ b/src/test/regress/expected/create_procedure.out
@@ -174,6 +174,10 @@ CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT INTO cp_test VALUES (
 ERROR:  invalid attribute in procedure definition
 LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT I...
                                                ^
+CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
+ERROR:  invalid attribute in procedure definition
+LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INS...
+                                               ^
 CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 ERROR:  invalid attribute in procedure definition
 LINE 1: CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT I...
diff --git a/src/test/regress/expected/misc_sanity.out b/src/test/regress/expected/misc_sanity.out
index d40afeef78..8615d78075 100644
--- a/src/test/regress/expected/misc_sanity.out
+++ b/src/test/regress/expected/misc_sanity.out
@@ -109,3 +109,13 @@ ORDER BY 1, 2;
  pg_largeobject_metadata | lomacl        | aclitem[]
 (11 rows)
 
+-- **************** pg_class ****************
+-- Look for non-window functions with null treatment (there should be none)
+SELECT proname, prokind, pronulltreatment
+FROM pg_proc
+WHERE pronulltreatment AND prokind <> 'w'
+ORDER BY oid;
+ proname | prokind | pronulltreatment 
+---------+---------+------------------
+(0 rows)
+
diff --git a/src/test/regress/expected/window.out b/src/test/regress/expected/window.out
index 19e2ac518a..3bd9584c6c 100644
--- a/src/test/regress/expected/window.out
+++ b/src/test/regress/expected/window.out
@@ -4063,3 +4063,214 @@ SELECT * FROM pg_temp.f(2);
  {5}
 (5 rows)
 
+-- IGNORE NULLS tests
+CREATE TEMPORARY TABLE planets (
+    name text,
+    orbit integer
+);
+INSERT INTO planets VALUES
+  ('mercury', 88),
+  ('venus', 224),
+  ('earth', NULL),
+  ('mars', NULL),
+  ('jupiter', 4332),
+  ('saturn', 24491),
+  ('uranus', NULL),
+  ('neptune', 60182),
+  ('pluto', 90560),
+  ('xyzzy', NULL);
+-- test ruleutils
+CREATE VIEW planets_view AS
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+NOTICE:  view "planets_view" will be a temporary view
+SELECT pg_get_viewdef('planets_view');
+                       pg_get_viewdef                        
+-------------------------------------------------------------
+  SELECT planets.name,                                      +
+     planets.orbit,                                         +
+     lag(planets.orbit) OVER w AS lag,                      +
+     lag(planets.orbit) RESPECT NULLS OVER w AS lag_respect,+
+     lag(planets.orbit) IGNORE NULLS OVER w AS lag_ignore   +
+    FROM planets                                            +
+   WINDOW w AS (ORDER BY planets.name);
+(1 row)
+
+-- lag
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+  name   | orbit |  lag  | lag_respect | lag_ignore 
+---------+-------+-------+-------------+------------
+ earth   |       |       |             |           
+ jupiter |  4332 |       |             |           
+ mars    |       |  4332 |        4332 |       4332
+ mercury |    88 |       |             |       4332
+ neptune | 60182 |    88 |          88 |         88
+ pluto   | 90560 | 60182 |       60182 |      60182
+ saturn  | 24491 | 90560 |       90560 |      90560
+ uranus  |       | 24491 |       24491 |      24491
+ venus   |   224 |       |             |      24491
+ xyzzy   |       |   224 |         224 |        224
+(10 rows)
+
+-- lead
+SELECT name,
+       orbit,
+       lead(orbit) OVER w AS lead,
+       lead(orbit) RESPECT NULLS OVER w AS lead_respect,
+       lead(orbit) IGNORE NULLS OVER w AS lead_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+  name   | orbit | lead  | lead_respect | lead_ignore 
+---------+-------+-------+--------------+-------------
+ earth   |       |  4332 |         4332 |        4332
+ jupiter |  4332 |       |              |          88
+ mars    |       |    88 |           88 |          88
+ mercury |    88 | 60182 |        60182 |       60182
+ neptune | 60182 | 90560 |        90560 |       90560
+ pluto   | 90560 | 24491 |        24491 |       24491
+ saturn  | 24491 |       |              |         224
+ uranus  |       |   224 |          224 |         224
+ venus   |   224 |       |              |            
+ xyzzy   |       |       |              |            
+(10 rows)
+
+-- first_value
+SELECT name,
+       orbit,
+       first_value(orbit) RESPECT NULLS OVER w1,
+       first_value(orbit) IGNORE NULLS OVER w1,
+       first_value(orbit) RESPECT NULLS OVER w2,
+       first_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | first_value | first_value | first_value | first_value 
+---------+-------+-------------+-------------+-------------+-------------
+ earth   |       |             |        4332 |             |        4332
+ jupiter |  4332 |             |        4332 |             |        4332
+ mars    |       |             |        4332 |             |        4332
+ mercury |    88 |             |        4332 |        4332 |        4332
+ neptune | 60182 |             |        4332 |             |          88
+ pluto   | 90560 |             |        4332 |          88 |          88
+ saturn  | 24491 |             |        4332 |       60182 |       60182
+ uranus  |       |             |        4332 |       90560 |       90560
+ venus   |   224 |             |        4332 |       24491 |       24491
+ xyzzy   |       |             |        4332 |             |         224
+(10 rows)
+
+-- nth_value
+SELECT name,
+       orbit,
+       nth_value(orbit, 2) RESPECT NULLS OVER w1,
+       nth_value(orbit, 2) IGNORE NULLS OVER w1,
+       nth_value(orbit, 2) RESPECT NULLS OVER w2,
+       nth_value(orbit, 2) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | nth_value | nth_value | nth_value | nth_value 
+---------+-------+-----------+-----------+-----------+-----------
+ earth   |       |      4332 |        88 |      4332 |          
+ jupiter |  4332 |      4332 |        88 |      4332 |        88
+ mars    |       |      4332 |        88 |      4332 |        88
+ mercury |    88 |      4332 |        88 |           |        88
+ neptune | 60182 |      4332 |        88 |        88 |     60182
+ pluto   | 90560 |      4332 |        88 |     60182 |     60182
+ saturn  | 24491 |      4332 |        88 |     90560 |     90560
+ uranus  |       |      4332 |        88 |     24491 |     24491
+ venus   |   224 |      4332 |        88 |           |       224
+ xyzzy   |       |      4332 |        88 |       224 |          
+(10 rows)
+
+-- last_value
+SELECT name,
+       orbit,
+       last_value(orbit) RESPECT NULLS OVER w1,
+       last_value(orbit) IGNORE NULLS OVER w1,
+       last_value(orbit) RESPECT NULLS OVER w2,
+       last_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+  name   | orbit | last_value | last_value | last_value | last_value 
+---------+-------+------------+------------+------------+------------
+ earth   |       |            |        224 |            |       4332
+ jupiter |  4332 |            |        224 |         88 |         88
+ mars    |       |            |        224 |      60182 |      60182
+ mercury |    88 |            |        224 |      90560 |      90560
+ neptune | 60182 |            |        224 |      24491 |      24491
+ pluto   | 90560 |            |        224 |            |      24491
+ saturn  | 24491 |            |        224 |        224 |        224
+ uranus  |       |            |        224 |            |        224
+ venus   |   224 |            |        224 |            |        224
+ xyzzy   |       |            |        224 |            |        224
+(10 rows)
+
+-- window function without null treatment
+SELECT row_number() OVER (ORDER BY name) FROM planets;
+ row_number 
+------------
+          1
+          2
+          3
+          4
+          5
+          6
+          7
+          8
+          9
+         10
+(10 rows)
+
+SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM planets; -- fails
+ERROR:  window function row_number does not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM ...
+               ^
+SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM planets; -- fails
+ERROR:  window function row_number does not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM p...
+               ^
+-- regular aggregate
+SELECT sum(orbit) OVER () FROM planets;
+  sum   
+--------
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+ 179877
+(10 rows)
+
+SELECT sum(orbit) RESPECT NULLS OVER () FROM planets; -- fails
+ERROR:  aggregate functions do not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT sum(orbit) RESPECT NULLS OVER () FROM planets;
+               ^
+SELECT sum(orbit) IGNORE NULLS OVER () FROM planets; -- fails
+ERROR:  aggregate functions do not accept RESPECT/IGNORE NULLS
+LINE 1: SELECT sum(orbit) IGNORE NULLS OVER () FROM planets;
+               ^
+--cleanup
+DROP TABLE planets CASCADE;
+NOTICE:  drop cascades to view planets_view
diff --git a/src/test/regress/sql/create_function_3.sql b/src/test/regress/sql/create_function_3.sql
index bd108a918f..f7fe984e58 100644
--- a/src/test/regress/sql/create_function_3.sql
+++ b/src/test/regress/sql/create_function_3.sql
@@ -82,6 +82,12 @@ SELECT proname, prosecdef FROM pg_proc
                      'functest_C_2'::regproc,
                      'functest_C_3'::regproc) ORDER BY proname;
 
+--
+-- TREAT NULLS
+--
+CREATE FUNCTION functest_D_1(integer) RETURNS integer LANGUAGE 'sql'
+       TREAT NULLS AS 'SELECT $1';
+
 --
 -- LEAKPROOF
 --
@@ -190,6 +196,7 @@ DROP FUNCTION functest_b_2;  -- error, ambiguous
 
 CREATE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL AS 'SELECT $1';
 CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL WINDOW AS 'SELECT $1';
+CREATE OR REPLACE FUNCTION functest1(a int) RETURNS int LANGUAGE SQL TREAT NULLS AS 'SELECT $1';
 CREATE OR REPLACE PROCEDURE functest1(a int) LANGUAGE SQL AS 'SELECT $1';
 DROP FUNCTION functest1(a int);
 
diff --git a/src/test/regress/sql/create_procedure.sql b/src/test/regress/sql/create_procedure.sql
index 2ef1c82cea..188f5f85a9 100644
--- a/src/test/regress/sql/create_procedure.sql
+++ b/src/test/regress/sql/create_procedure.sql
@@ -130,6 +130,7 @@ CALL version();  -- error: not a procedure
 CALL sum(1);  -- error: not a procedure
 
 CREATE PROCEDURE ptestx() LANGUAGE SQL WINDOW AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
+CREATE PROCEDURE ptestx() LANGUAGE SQL TREAT NULLS AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 CREATE PROCEDURE ptestx() LANGUAGE SQL STRICT AS $$ INSERT INTO cp_test VALUES (1, 'a') $$;
 
 ALTER PROCEDURE ptest1(text) STRICT;
diff --git a/src/test/regress/sql/misc_sanity.sql b/src/test/regress/sql/misc_sanity.sql
index 3ce32e4725..ccb4f008d9 100644
--- a/src/test/regress/sql/misc_sanity.sql
+++ b/src/test/regress/sql/misc_sanity.sql
@@ -94,3 +94,12 @@ WHERE c.oid < 16384 AND
       relkind = 'r' AND
       attstorage != 'p'
 ORDER BY 1, 2;
+
+-- **************** pg_class ****************
+
+-- Look for non-window functions with null treatment (there should be none)
+
+SELECT proname, prokind, pronulltreatment
+FROM pg_proc
+WHERE pronulltreatment AND prokind <> 'w'
+ORDER BY oid;
diff --git a/src/test/regress/sql/window.sql b/src/test/regress/sql/window.sql
index eae5fa6017..a021ed3544 100644
--- a/src/test/regress/sql/window.sql
+++ b/src/test/regress/sql/window.sql
@@ -1328,3 +1328,104 @@ $$ LANGUAGE SQL STABLE;
 
 EXPLAIN (costs off) SELECT * FROM pg_temp.f(2);
 SELECT * FROM pg_temp.f(2);
+
+
+-- IGNORE NULLS tests
+
+CREATE TEMPORARY TABLE planets (
+    name text,
+    orbit integer
+);
+
+INSERT INTO planets VALUES
+  ('mercury', 88),
+  ('venus', 224),
+  ('earth', NULL),
+  ('mars', NULL),
+  ('jupiter', 4332),
+  ('saturn', 24491),
+  ('uranus', NULL),
+  ('neptune', 60182),
+  ('pluto', 90560),
+  ('xyzzy', NULL);
+
+-- test ruleutils
+CREATE VIEW planets_view AS
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+SELECT pg_get_viewdef('planets_view');
+
+-- lag
+SELECT name,
+       orbit,
+       lag(orbit) OVER w AS lag,
+       lag(orbit) RESPECT NULLS OVER w AS lag_respect,
+       lag(orbit) IGNORE NULLS OVER w AS lag_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+
+-- lead
+SELECT name,
+       orbit,
+       lead(orbit) OVER w AS lead,
+       lead(orbit) RESPECT NULLS OVER w AS lead_respect,
+       lead(orbit) IGNORE NULLS OVER w AS lead_ignore
+FROM planets
+WINDOW w AS (ORDER BY name)
+;
+
+-- first_value
+SELECT name,
+       orbit,
+       first_value(orbit) RESPECT NULLS OVER w1,
+       first_value(orbit) IGNORE NULLS OVER w1,
+       first_value(orbit) RESPECT NULLS OVER w2,
+       first_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- nth_value
+SELECT name,
+       orbit,
+       nth_value(orbit, 2) RESPECT NULLS OVER w1,
+       nth_value(orbit, 2) IGNORE NULLS OVER w1,
+       nth_value(orbit, 2) RESPECT NULLS OVER w2,
+       nth_value(orbit, 2) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- last_value
+SELECT name,
+       orbit,
+       last_value(orbit) RESPECT NULLS OVER w1,
+       last_value(orbit) IGNORE NULLS OVER w1,
+       last_value(orbit) RESPECT NULLS OVER w2,
+       last_value(orbit) IGNORE NULLS OVER w2
+FROM planets
+WINDOW w1 AS (ORDER BY name ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING),
+       w2 AS (ORDER BY name ROWS BETWEEN 2 PRECEDING AND 2 FOLLOWING)
+;
+
+-- window function without null treatment
+SELECT row_number() OVER (ORDER BY name) FROM planets;
+SELECT row_number() RESPECT NULLS OVER (ORDER BY name) FROM planets; -- fails
+SELECT row_number() IGNORE NULLS OVER (ORDER BY name) FROM planets; -- fails
+
+-- regular aggregate
+SELECT sum(orbit) OVER () FROM planets;
+SELECT sum(orbit) RESPECT NULLS OVER () FROM planets; -- fails
+SELECT sum(orbit) IGNORE NULLS OVER () FROM planets; -- fails
+
+--cleanup
+DROP TABLE planets CASCADE;