Re: Function scan FDW pushdown

Alexander Pyhalov Tue, 07 Jul 2026 03:25:39 -0700

Alexander Korotkov писал(а) 2026-07-06 17:11:

Hi, Alexander!


On Wed, May 20, 2026 at 1:17 PM Alexander Pyhalov
<[email protected]> wrote:

I've found another issue. The fact that in the new versions of thepatchRTE RelOptInfo misses fdw_private seems to be unfortunate. Forexample,

in the last version we haven't thought about classifying
baserestrictinfo. And if we do, we should pass fdw_private down to
foreign_expr_walker. Perhaps, we could attach it to RTE_FUNCTION rel
prior to calling classifyConditions(), but should we later set it back
to NULL? Another problem comes if we try to handle joins,  which can
crearte subqueries (like INNER/OUTER UNIQUE). In this case we should

somehow cook fpinfo for get_relation_column_alias_ids(). Attachingpatch

which tries to handle baserestrictinfos by passing fpinfo down to
foreign_expr_walker().


I think passing fpinfo down to foreign_expr_walker() is the right
approach, thank you.  Attaching it to RTE_FUNCTION rel, and reseting
it back to NULL would create excessive state and potential source of
bugs.  The only advantage is saving existing function signatures, but
it doesn't worth it.

Also, I don't think we need to care bout
get_relation_column_alias_ids().  As we currently pushdown function
only for inner joins, make_outerrel_subquery/make_innerrel_subquery
are always false, lower_subquery_rels also wouldn't contain
RTE_FUNCTION relid.
 Therefore:

 * In deparseFromExprForRel() for functional rel deparseRangeTblRef()
is always called with make_subquery=false.
 * is_subquery_var() returns false.


Well, at least current patch version classifies conditions correctly.

Other changes I made:

1. In foreign_join_ok(), the function side's baserestrictinfo was
classified against the joinrel fpinfo, whose
server/shippable_extensions aren't set until merge_fdw_options() runs
later — so extension-shippable quals would be misclassified as local
and silently kill the pushdown. Now it: (a) copies
shippable_extensions from the foreign side onto the stub, and (b)
classifies against the stub (fpinfo_i/fpinfo_o, which already has
server). Built-in quals like n > 3 were unaffected; this fixes the
extension case.  I've added the test case for this.

2. Dropped unused funcid. The per-RTE metadata was a 3-element list
(funcid, funcrettype, funccollation) but funcid was never read.
Reduced to list_make2(funcrettype, funccollation); updated the
consumer (linitial/lsecond) and both descriptive comments.


With funcid we could print actual function name in explain.
Now we print, for example,

Relations: ((public.distr1_part_3 d1_3) INNER JOIN (public.distr2_part_3d2_3)) INNER JOIN (Function n)

If funcid is preserved, we could output actual function name instead ofalias. This is more similar tohow we show relation names. Attaching updated patch, which preservesfunction names in explain.

After looking at it once more, I'm not convinced when we can getnot-FuncExpr in rtfunc->funcexpr.So added more checks to function_rte_pushdown_ok() to avoid dealing withsuch case.

--
Best regards,
Alexander Pyhalov,
Postgres Professional

From b850713b648ed985816c733552db40d613294005 Mon Sep 17 00:00:00 2001
From: Alexander Korotkov <[email protected]>
Date: Tue, 7 Jul 2026 09:57:19 +0300
Subject: [PATCH] postgres_fdw: push down FUNCTION RTE into foreign joins

A foreign join planning hook now considers a (foreign-table x function-RTE)
INNER join as a push-down candidate when the function expression is
IMMUTABLE and otherwise shippable.  The remote query absorbs the function
call as a FROM-list item (e.g. unnest(...) AS f<rti>(c1, c2, ...)), so the
foreign side returns only rows that match the function-produced set and the
join executes entirely on the remote.

An IMMUTABLE function gives the same result on any server, so the same
function RTE can be a push-down candidate for several distinct foreign
servers without semantic risk.  To keep the planner state consistent
across those independent attempts, the per-call stub fpinfo for the
function side lives on the joinrel's PgFdwRelationInfo (new
outer_func_fpinfo / inner_func_fpinfo), never on the function rel itself,
and the function side is detected via rtekind rather than fdw_private.

set_foreign_rel_properties() propagates fdwroutine onto a joinrel that
pairs a foreign rel with an RTE_FUNCTION rel so GetForeignJoinPaths gets
called; the FDW retains full control over whether to actually generate a
path.  deparseRangeTblRef and deparseColumnRef gain a FUNCTION-RTE branch
that emits the function expression and resolves Vars to the generated
---
 contrib/postgres_fdw/deparse.c                | 143 +++-
 .../postgres_fdw/expected/postgres_fdw.out    | 631 ++++++++++++++++++
 contrib/postgres_fdw/postgres_fdw.c           | 608 +++++++++++++++--
 contrib/postgres_fdw/postgres_fdw.h           |  12 +
 contrib/postgres_fdw/sql/postgres_fdw.sql     | 265 ++++++++
 src/backend/optimizer/util/relnode.c          |  24 +
 6 files changed, 1626 insertions(+), 57 deletions(-)

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index 2dcc6c8af1b..a2e9301fb65 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -68,6 +68,7 @@ typedef struct foreign_glob_cxt
 {
 	PlannerInfo *root;			/* global planner state */
 	RelOptInfo *foreignrel;		/* the foreign relation we are planning for */
+	PgFdwRelationInfo *fpinfo;	/* the foreign server info we should rely on */
 	Relids		relids;			/* relids of base relations in the underlying
 								 * scan */
 } foreign_glob_cxt;
@@ -112,6 +113,7 @@ typedef struct deparse_expr_cxt
 		appendStringInfo((buf), "%s%d.", REL_ALIAS_PREFIX, (varno))
 #define SUBQUERY_REL_ALIAS_PREFIX	"s"
 #define SUBQUERY_COL_ALIAS_PREFIX	"c"
+#define FUNCTION_REL_ALIAS_PREFIX	"f"
 
 /*
  * Functions to determine whether an expression can be evaluated safely on
@@ -217,6 +219,7 @@ static void get_relation_column_alias_ids(Var *node, RelOptInfo *foreignrel,
 void
 classifyConditions(PlannerInfo *root,
 				   RelOptInfo *baserel,
+				   PgFdwRelationInfo *fpinfo,
 				   List *input_conds,
 				   List **remote_conds,
 				   List **local_conds)
@@ -230,7 +233,7 @@ classifyConditions(PlannerInfo *root,
 	{
 		RestrictInfo *ri = lfirst_node(RestrictInfo, lc);
 
-		if (is_foreign_expr(root, baserel, ri->clause))
+		if (is_foreign_expr(root, baserel, fpinfo, ri->clause))
 			*remote_conds = lappend(*remote_conds, ri);
 		else
 			*local_conds = lappend(*local_conds, ri);
@@ -243,11 +246,11 @@ classifyConditions(PlannerInfo *root,
 bool
 is_foreign_expr(PlannerInfo *root,
 				RelOptInfo *baserel,
+				PgFdwRelationInfo *fpinfo,
 				Expr *expr)
 {
 	foreign_glob_cxt glob_cxt;
 	foreign_loc_cxt loc_cxt;
-	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) (baserel->fdw_private);
 
 	/*
 	 * Check that the expression consists of nodes that are safe to execute
@@ -255,6 +258,7 @@ is_foreign_expr(PlannerInfo *root,
 	 */
 	glob_cxt.root = root;
 	glob_cxt.foreignrel = baserel;
+	glob_cxt.fpinfo = fpinfo;
 
 	/*
 	 * For an upper relation, use relids from its underneath scan relation,
@@ -324,8 +328,8 @@ foreign_expr_walker(Node *node,
 	if (node == NULL)
 		return true;
 
-	/* May need server info from baserel's fdw_private struct */
-	fpinfo = (PgFdwRelationInfo *) (glob_cxt->foreignrel->fdw_private);
+	/* May need server info from global context */
+	fpinfo = glob_cxt->fpinfo;
 
 	/* Set up inner_cxt for possible recursion to child nodes */
 	inner_cxt.collation = InvalidOid;
@@ -2030,6 +2034,72 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 	}
 }
 
+/*
+ * Deparse a FUNCTION RTE absorbed into a foreign join.  The function call(s)
+ * are emitted as a FROM-list item:
+ *
+ *   <funcexpr> AS f<rti>(c1, c2, ..., cN)
+ *
+ * For multi-function RTEs (SQL ROWS FROM (f1(), f2(), ...)), each
+ * function call appears comma-separated inside ROWS FROM(...).  Column
+ * aliases c1..cN cover the union of every function's columns, in the
+ * order they appear; that matches the column ordering of the RTE.
+ */
+static void
+deparseFunctionRangeTblRef(StringInfo buf, PlannerInfo *root,
+						   RelOptInfo *foreignrel, RelOptInfo *scanrel,
+						   List **params_list)
+{
+	RangeTblEntry *rte = planner_rt_fetch(foreignrel->relid, root);
+	deparse_expr_cxt context;
+	ListCell   *lc;
+	bool		multi_func;
+	int			total_cols = 0;
+	int			i;
+
+	Assert(rte->rtekind == RTE_FUNCTION);
+	Assert(!rte->funcordinality);
+	Assert(list_length(rte->functions) >= 1);
+
+	multi_func = list_length(rte->functions) > 1;
+
+	context.buf = buf;
+	context.root = root;
+	context.foreignrel = scanrel;
+	context.scanrel = scanrel;
+	context.params_list = params_list;
+
+	if (multi_func)
+		appendStringInfoString(buf, "ROWS FROM (");
+
+	foreach(lc, rte->functions)
+	{
+		RangeTblFunction *rtfunc = (RangeTblFunction *) lfirst(lc);
+
+		if (foreach_current_index(lc) > 0)
+			appendStringInfoString(buf, ", ");
+		deparseExpr((Expr *) rtfunc->funcexpr, &context);
+		total_cols += rtfunc->funccolcount;
+	}
+
+	if (multi_func)
+		appendStringInfoChar(buf, ')');
+
+	/* Alias + generated column-name list. */
+	appendStringInfo(buf, " %s%d", FUNCTION_REL_ALIAS_PREFIX, foreignrel->relid);
+	if (total_cols > 0)
+	{
+		appendStringInfoChar(buf, '(');
+		for (i = 1; i <= total_cols; i++)
+		{
+			if (i > 1)
+				appendStringInfoString(buf, ", ");
+			appendStringInfo(buf, "%s%d", SUBQUERY_COL_ALIAS_PREFIX, i);
+		}
+		appendStringInfoChar(buf, ')');
+	}
+}
+
 /*
  * Append FROM clause entry for the given relation into buf.
  * Conditions from lower-level SEMI-JOINs are appended to additional_conds
@@ -2040,7 +2110,22 @@ deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
 				   bool make_subquery, Index ignore_rel, List **ignore_conds,
 				   List **additional_conds, List **params_list)
 {
-	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
+	PgFdwRelationInfo *fpinfo;
+
+	/*
+	 * For a function RTE absorbed into a foreign join, deparse the function
+	 * expression as a FROM-list item and return.  The stub fpinfo set up by
+	 * foreign_join_ok() may or may not be present here.
+	 */
+	if (foreignrel->rtekind == RTE_FUNCTION)
+	{
+		Assert(!make_subquery);
+		deparseFunctionRangeTblRef(buf, root, foreignrel, foreignrel,
+								   params_list);
+		return;
+	}
+
+	fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
 	/* Should only be called in these cases. */
 	Assert(IS_SIMPLE_REL(foreignrel) || IS_JOIN_REL(foreignrel));
@@ -2712,6 +2797,54 @@ static void
 deparseColumnRef(StringInfo buf, int varno, int varattno, RangeTblEntry *rte,
 				 bool qualify_col)
 {
+	/*
+	 * Function RTE columns: emit as f<varno>.c<varattno>, matching the
+	 * aliases generated by deparseFunctionRangeTblRef().  A whole-row Var
+	 * (varattno == 0) is rendered as ROW(f<varno>.c1, ..., f<varno>.c<N>)
+	 * where N is the total column count of the function RTE (including all
+	 * ROWS FROM (...) members).  System attributes such as ctid have no
+	 * meaning for function RTEs and are rejected.
+	 */
+	if (rte->rtekind == RTE_FUNCTION)
+	{
+		if (varattno == 0)
+		{
+			int			ncols = list_length(rte->eref->colnames);
+			int			i;
+
+			if (qualify_col)
+			{
+				appendStringInfoString(buf, "CASE WHEN (");
+				appendStringInfo(buf, "%s%d.", FUNCTION_REL_ALIAS_PREFIX, varno);
+				appendStringInfoString(buf, "*)::text IS NOT NULL THEN ");
+			}
+
+			appendStringInfoString(buf, "ROW(");
+			for (i = 1; i <= ncols; i++)
+			{
+				if (i > 1)
+					appendStringInfoString(buf, ", ");
+				appendStringInfo(buf, "%s%d.%s%d",
+								 FUNCTION_REL_ALIAS_PREFIX, varno,
+								 SUBQUERY_COL_ALIAS_PREFIX, i);
+			}
+			appendStringInfoChar(buf, ')');
+
+			if (qualify_col)
+				appendStringInfoString(buf, " END");
+			return;
+		}
+
+		if (varattno < 0)
+			elog(ERROR,
+				 "system attribute reference to a function RTE is not supported in foreign join pushdown");
+
+		if (qualify_col)
+			appendStringInfo(buf, "%s%d.", FUNCTION_REL_ALIAS_PREFIX, varno);
+		appendStringInfo(buf, "%s%d", SUBQUERY_COL_ALIAS_PREFIX, varattno);
+		return;
+	}
+
 	/* We support fetching the remote side's CTID and OID. */
 	if (varattno == SelfItemPointerAttributeNumber)
 	{
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index aaffcf31271..e3355aa8a86 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -2885,6 +2885,637 @@ SELECT t1.c1, t2.c2 FROM v4 t1 LEFT JOIN ft5 t2 ON (t1.c1 = t2.c1) ORDER BY t1.c
 (10 rows)
 
 ALTER VIEW v4 OWNER TO regress_view_owner;
+-- ===================================================================
+-- Foreign-join with FUNCTION RTE pushdown (IMMUTABLE functions only)
+-- ===================================================================
+-- IMMUTABLE function: unnest of constant array can be pushed down
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1, t1.c3 FROM ft1 t1, unnest(ARRAY[1, 5, 10, 100]::int[]) AS u(id)
+WHERE t1.c1 = u.id ORDER BY t1.c1;
+                                                                   QUERY PLAN                                                                   
+------------------------------------------------------------------------------------------------------------------------------------------------
+ Sort
+   Output: t1.c1, t1.c3
+   Sort Key: t1.c1
+   ->  Foreign Scan
+         Output: t1.c1, t1.c3
+         Relations: (public.ft1 t1) INNER JOIN (pg_catalog.unnest() u)
+         Remote SQL: SELECT r1."C 1", r1.c3 FROM ("S 1"."T 1" r1 INNER JOIN unnest('{1,5,10,100}'::integer[]) f2(c1) ON (((r1."C 1" = f2.c1))))
+(7 rows)
+
+SELECT t1.c1, t1.c3 FROM ft1 t1, unnest(ARRAY[1, 5, 10, 100]::int[]) AS u(id)
+WHERE t1.c1 = u.id ORDER BY t1.c1;
+ c1  |  c3   
+-----+-------
+   1 | 00001
+   5 | 00005
+  10 | 00010
+ 100 | 00100
+(4 rows)
+
+-- IMMUTABLE function: generate_series with constant args
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1 FROM ft1 t1, generate_series(1, 4) AS g(id)
+WHERE t1.c1 = g.id ORDER BY t1.c1;
+                                                         QUERY PLAN                                                          
+-----------------------------------------------------------------------------------------------------------------------------
+ Sort
+   Output: t1.c1
+   Sort Key: t1.c1
+   ->  Foreign Scan
+         Output: t1.c1
+         Relations: (public.ft1 t1) INNER JOIN (pg_catalog.generate_series() g)
+         Remote SQL: SELECT r1."C 1" FROM ("S 1"."T 1" r1 INNER JOIN generate_series(1, 4) f2(c1) ON (((r1."C 1" = f2.c1))))
+(7 rows)
+
+SELECT t1.c1 FROM ft1 t1, generate_series(1, 4) AS g(id)
+WHERE t1.c1 = g.id ORDER BY t1.c1;
+ c1 
+----
+  1
+  2
+  3
+  4
+(4 rows)
+
+-- VOLATILE function (random) must NOT be pushed down
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1 FROM ft1 t1, generate_series(1, 4 + (random() * 0)::int) AS g(id)
+WHERE t1.c1 = g.id;
+                                           QUERY PLAN                                           
+------------------------------------------------------------------------------------------------
+ Hash Join
+   Output: t1.c1
+   Hash Cond: (g.id = t1.c1)
+   ->  Function Scan on pg_catalog.generate_series g
+         Output: g.id
+         Function Call: generate_series(1, (4 + ((random() * '0'::double precision))::integer))
+   ->  Hash
+         Output: t1.c1
+         ->  Foreign Scan on public.ft1 t1
+               Output: t1.c1
+               Remote SQL: SELECT "C 1" FROM "S 1"."T 1"
+(11 rows)
+
+-- WITH ORDINALITY must NOT be pushed down (limitation of this implementation)
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1, u.ord
+FROM ft1 t1, unnest(ARRAY[1, 5, 10]::int[]) WITH ORDINALITY AS u(id, ord)
+WHERE t1.c1 = u.id;
+                         QUERY PLAN                         
+------------------------------------------------------------
+ Hash Join
+   Output: t1.c1, u.ord
+   Hash Cond: (t1.c1 = u.id)
+   ->  Foreign Scan on public.ft1 t1
+         Output: t1.c1
+         Remote SQL: SELECT "C 1" FROM "S 1"."T 1"
+   ->  Hash
+         Output: u.ord, u.id
+         ->  Function Scan on pg_catalog.unnest u
+               Output: u.ord, u.id
+               Function Call: unnest('{1,5,10}'::integer[])
+(11 rows)
+
+-- Same function RTE joined with two different foreign servers: planner picks
+-- one absorption + a local join with the second foreign server.  The fact
+-- that the function is IMMUTABLE makes this safe even if both sides chose to
+-- absorb it independently.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1, t2.c1
+FROM ft1 t1, ft6 t2, unnest(ARRAY[1, 5, 10, 100]::int[]) AS u(id)
+WHERE t1.c1 = u.id AND t2.c1 = u.id ORDER BY t1.c1;
+                                                                   QUERY PLAN                                                                   
+------------------------------------------------------------------------------------------------------------------------------------------------
+ Merge Join
+   Output: t1.c1, t2.c1
+   Merge Cond: (t1.c1 = u.id)
+   ->  Foreign Scan on public.ft1 t1
+         Output: t1.c1
+         Remote SQL: SELECT "C 1" FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
+   ->  Sort
+         Output: t2.c1, u.id
+         Sort Key: t2.c1
+         ->  Foreign Scan
+               Output: t2.c1, u.id
+               Relations: (public.ft6 t2) INNER JOIN (pg_catalog.unnest() u)
+               Remote SQL: SELECT r2.c1, f3.c1 FROM ("S 1"."T 4" r2 INNER JOIN unnest('{1,5,10,100}'::integer[]) f3(c1) ON (((r2.c1 = f3.c1))))
+(13 rows)
+
+-- Cost-based selection between two foreign servers: ft1 ("S 1"."T 1") has
+-- 1000 rows, ft6 ("S 1"."T 4") has ~33 rows.  The same query shape gets a
+-- different push-down target depending on a predicate that changes the
+-- effective cardinality of one side -- the function "jumps" to whichever
+-- foreign scan benefits more from being pre-filtered.
+ANALYZE ft1;
+ANALYZE ft6;
+-- No extra predicate: ft1 is the bigger side, function absorbed there.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1, t2.c1
+FROM ft1 t1, ft6 t2, unnest(ARRAY[3, 6, 9, 12, 15, 18]::int[]) AS u(id)
+WHERE t1.c1 = u.id AND t2.c1 = u.id;
+                                                                     QUERY PLAN                                                                     
+----------------------------------------------------------------------------------------------------------------------------------------------------
+ Hash Join
+   Output: t1.c1, t2.c1
+   Hash Cond: (t1.c1 = t2.c1)
+   ->  Foreign Scan
+         Output: t1.c1, u.id
+         Relations: (public.ft1 t1) INNER JOIN (pg_catalog.unnest() u)
+         Remote SQL: SELECT r1."C 1", f3.c1 FROM ("S 1"."T 1" r1 INNER JOIN unnest('{3,6,9,12,15,18}'::integer[]) f3(c1) ON (((r1."C 1" = f3.c1))))
+   ->  Hash
+         Output: t2.c1
+         ->  Foreign Scan on public.ft6 t2
+               Output: t2.c1
+               Remote SQL: SELECT c1 FROM "S 1"."T 4"
+(12 rows)
+
+-- Selective predicate on ft1.c3 (not in the eqclass) shrinks ft1 to a
+-- handful of remote rows; now ft6 is effectively the bigger side and the
+-- function is absorbed into ft6 instead.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1, t2.c1
+FROM ft1 t1, ft6 t2, unnest(ARRAY[3, 6, 9, 12, 15, 18]::int[]) AS u(id)
+WHERE t1.c1 = u.id AND t2.c1 = u.id AND t1.c3 < '00010';
+                                                                     QUERY PLAN                                                                     
+----------------------------------------------------------------------------------------------------------------------------------------------------
+ Nested Loop
+   Output: t1.c1, t2.c1
+   Join Filter: (t1.c1 = u.id)
+   ->  Foreign Scan on public.ft1 t1
+         Output: t1.c1
+         Remote SQL: SELECT "C 1" FROM "S 1"."T 1" WHERE ((c3 < '00010'))
+   ->  Materialize
+         Output: t2.c1, u.id
+         ->  Foreign Scan
+               Output: t2.c1, u.id
+               Relations: (public.ft6 t2) INNER JOIN (pg_catalog.unnest() u)
+               Remote SQL: SELECT r2.c1, f3.c1 FROM ("S 1"."T 4" r2 INNER JOIN unnest('{3,6,9,12,15,18}'::integer[]) f3(c1) ON (((r2.c1 = f3.c1))))
+(12 rows)
+
+-- The remaining scenarios reuse a dedicated foreign table to cover the
+-- corner cases of FUNCTION RTE push-down: function-first FROM, record
+-- return type rejection, whole-row reference, UPDATE...FROM..., and
+-- multi-function ROWS FROM.
+CREATE TABLE base_tbl_fn (a int, b int);
+INSERT INTO base_tbl_fn
+  SELECT g, g + 100 FROM generate_series(1, 30) g;
+CREATE FOREIGN TABLE remote_tbl (a int, b int)
+  SERVER loopback OPTIONS (table_name 'base_tbl_fn');
+-- The function RTE appears first in FROM; the foreign relation must be
+-- found by scanning fs_base_relids for an RTE_RELATION rather than
+-- using scan->fs_relid blindly.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r WHERE r.a = n;
+                                                                QUERY PLAN                                                                
+------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: n.n, r.a, r.b
+   Relations: (pg_catalog.unnest() n) INNER JOIN (public.remote_tbl r)
+   Remote SQL: SELECT f1.c1, r2.a, r2.b FROM (unnest('{2,3,4}'::integer[]) f1(c1) INNER JOIN public.base_tbl_fn r2 ON (((f1.c1 = r2.a))))
+(4 rows)
+
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r
+WHERE r.a = n ORDER BY r.a;
+ n | a |  b  
+---+---+-----
+ 2 | 2 | 102
+ 3 | 3 | 103
+ 4 | 4 | 104
+(3 rows)
+
+-- Function RTE is restricted, shippable conditions
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r WHERE r.a = n and n > 3;
+                                                                         QUERY PLAN                                                                         
+------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: n.n, r.a, r.b
+   Relations: (pg_catalog.unnest() n) INNER JOIN (public.remote_tbl r)
+   Remote SQL: SELECT f1.c1, r2.a, r2.b FROM (unnest('{2,3,4}'::integer[]) f1(c1) INNER JOIN public.base_tbl_fn r2 ON (((f1.c1 = r2.a)) AND ((f1.c1 > 3))))
+(4 rows)
+
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r
+WHERE r.a = n and n > 3 ORDER BY r.a;
+ n | a |  b  
+---+---+-----
+ 4 | 4 | 104
+(1 row)
+
+-- Function RTE is restricted, nonshippable conditions
+CREATE FUNCTION f_local(int) RETURNS int AS $$
+BEGIN
+RETURN $1;
+END
+$$ LANGUAGE plpgsql;
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r WHERE r.a = n and n > f_local(3);
+                        QUERY PLAN                         
+-----------------------------------------------------------
+ Hash Join
+   Output: n.n, r.a, r.b
+   Hash Cond: (r.a = n.n)
+   ->  Foreign Scan on public.remote_tbl r
+         Output: r.a, r.b
+         Remote SQL: SELECT a, b FROM public.base_tbl_fn
+   ->  Hash
+         Output: n.n
+         ->  Function Scan on pg_catalog.unnest n
+               Output: n.n
+               Function Call: unnest('{2,3,4}'::integer[])
+               Filter: (n.n > f_local(3))
+(12 rows)
+
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r
+WHERE r.a = n and n > f_local(3) ORDER BY r.a;
+ n | a |  b  
+---+---+-----
+ 4 | 4 | 104
+(1 row)
+
+DROP FUNCTION f_local(int);
+-- Check that a qual on the function RTE using a function from a shippable
+-- extension is pushed down.  plpgsql (not inlined) with the column as
+-- argument (not const-folded) keeps the function call in the qual.
+CREATE FUNCTION f_ext(int) RETURNS int AS $$
+BEGIN RETURN $1; END
+$$ LANGUAGE plpgsql IMMUTABLE;
+ALTER EXTENSION postgres_fdw ADD FUNCTION f_ext(int);
+-- Force pushdown so the fixed-code plan is deterministically a Foreign
+-- Scan; on the unfixed code the qual is classified local, the join is
+-- refused, and the plan falls back to a local join instead.
+SET enable_hashjoin = off;
+SET enable_mergejoin = off;
+SET enable_nestloop = off;
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r WHERE r.a = n and f_ext(n) > 3;
+                                                                                QUERY PLAN                                                                                
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: n.n, r.a, r.b
+   Relations: (pg_catalog.unnest() n) INNER JOIN (public.remote_tbl r)
+   Remote SQL: SELECT f1.c1, r2.a, r2.b FROM (unnest('{2,3,4}'::integer[]) f1(c1) INNER JOIN public.base_tbl_fn r2 ON (((f1.c1 = r2.a)) AND ((public.f_ext(f1.c1) > 3))))
+(4 rows)
+
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r
+WHERE r.a = n and f_ext(n) > 3 ORDER BY r.a;
+ n | a |  b  
+---+---+-----
+ 4 | 4 | 104
+(1 row)
+
+RESET enable_hashjoin;
+RESET enable_mergejoin;
+RESET enable_nestloop;
+ALTER EXTENSION postgres_fdw DROP FUNCTION f_ext(int);
+DROP FUNCTION f_ext(int);
+-- A function returning record (composite) is forbidden; pushing it
+-- would yield a remote "column definition list is required" error.
+-- function_rte_pushdown_ok() rejects it via TYPEFUNC_SCALAR.
+CREATE OR REPLACE FUNCTION f_ret_record() RETURNS record AS $$
+  SELECT (1, 2)::record
+$$ LANGUAGE SQL IMMUTABLE;
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT s FROM remote_tbl rt, f_ret_record() AS s(a int, b int)
+WHERE s.a = rt.a;
+                      QUERY PLAN                      
+------------------------------------------------------
+ Hash Join
+   Output: s.*
+   Hash Cond: (rt.a = s.a)
+   ->  Foreign Scan on public.remote_tbl rt
+         Output: rt.a, rt.b
+         Remote SQL: SELECT a FROM public.base_tbl_fn
+   ->  Hash
+         Output: s.*, s.a
+         ->  Function Scan on public.f_ret_record s
+               Output: s.*, s.a
+               Function Call: f_ret_record()
+(11 rows)
+
+DROP FUNCTION f_ret_record();
+-- UPDATE ... FROM unnest() with a complex element type; area(box)
+-- yields the value to match.  The locking machinery for the
+-- non-relation RTE generates a whole-row Var that deparseColumnRef
+-- emits as ROW(f<rti>.c1, ...).
+UPDATE remote_tbl r SET b = 999
+FROM unnest(array[box '((2,3),(-2,-3))']) AS t(bx)
+WHERE r.a = area(t.bx);
+SELECT * FROM remote_tbl WHERE a IN (23, 24, 25) ORDER BY a;
+ a  |  b  
+----+-----
+ 23 | 123
+ 24 | 999
+ 25 | 125
+(3 rows)
+
+-- The same shape with CASE and RETURNING; exercises the DirectModify
+-- path and the executor's tuple-desc reconstruction.
+UPDATE remote_tbl r
+   SET b = CASE WHEN random() >= 0 THEN 5 ELSE 0 END
+  FROM unnest(array[box '((2,3),(-2,-3))']) AS t(bx)
+ WHERE r.a = area(t.bx) RETURNING a, b;
+ a  | b 
+----+---
+ 24 | 5
+(1 row)
+
+-- RETURNING a whole-row reference to the function RTE.  Without the
+-- per-RTE function metadata being preserved on the DirectModify path
+-- (FdwDirectModifyPrivateFunctions / FdwDirectModifyPrivateMinRTIndex),
+-- this would fail with "input of anonymous composite types is not
+-- implemented".
+UPDATE remote_tbl r SET b = 7
+  FROM unnest(array[box '((2,3),(-2,-3))'],
+              array[int '1']) AS t(bx, i)
+ WHERE r.a = area(t.bx) RETURNING a, b, t;
+ a  | b |          t          
+----+---+---------------------
+ 24 | 7 | ("(2,3),(-2,-3)",1)
+(1 row)
+
+-- ROWS FROM (...) with several functions.  Force pushdown because the
+-- cost model otherwise picks a local plan.
+SET enable_hashjoin = off;
+SET enable_mergejoin = off;
+SET enable_nestloop = off;
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT r.a, t.n, t.s
+  FROM remote_tbl r, ROWS FROM (unnest(array[3, 6, 9]),
+                                generate_series(11, 13)) AS t(n, s)
+ WHERE r.a = t.n ORDER BY r.a;
+                                                                                        QUERY PLAN                                                                                        
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Sort
+   Output: r.a, t.n, t.s
+   Sort Key: r.a
+   ->  Foreign Scan
+         Output: r.a, t.n, t.s
+         Relations: (public.remote_tbl r) INNER JOIN (ROWS FROM (pg_catalog.unnest(), pg_catalog.generate_series()) t)
+         Remote SQL: SELECT r1.a, f2.c1, f2.c2 FROM (public.base_tbl_fn r1 INNER JOIN ROWS FROM (unnest('{3,6,9}'::integer[]), generate_series(11, 13)) f2(c1, c2) ON (((r1.a = f2.c1))))
+(7 rows)
+
+SELECT r.a, t.n, t.s
+  FROM remote_tbl r, ROWS FROM (unnest(array[3, 6, 9]),
+                                generate_series(11, 13)) AS t(n, s)
+ WHERE r.a = t.n ORDER BY r.a;
+ a | n | s  
+---+---+----
+ 3 | 3 | 11
+ 6 | 6 | 12
+ 9 | 9 | 13
+(3 rows)
+
+-- Whole-row Var on the absorbed function side (e.g. via a cast to
+-- text).  Exercises both deparseColumnRef whole-row branch and the
+-- get_tupdesc_for_join_scan_tuples() RTE_FUNCTION metadata path.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t::text, r.a
+  FROM remote_tbl r, ROWS FROM (unnest(array[3, 6, 9]),
+                                generate_series(11, 13)) AS t(n, s)
+ WHERE r.a = t.n ORDER BY r.a;
+                                                                                                                QUERY PLAN                                                                                                                 
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Sort
+   Output: ((t.*)::text), r.a
+   Sort Key: r.a
+   ->  Foreign Scan
+         Output: (t.*)::text, r.a
+         Relations: (public.remote_tbl r) INNER JOIN (ROWS FROM (pg_catalog.unnest(), pg_catalog.generate_series()) t)
+         Remote SQL: SELECT CASE WHEN (f2.*)::text IS NOT NULL THEN ROW(f2.c1, f2.c2) END, r1.a FROM (public.base_tbl_fn r1 INNER JOIN ROWS FROM (unnest('{3,6,9}'::integer[]), generate_series(11, 13)) f2(c1, c2) ON (((r1.a = f2.c1))))
+(7 rows)
+
+SELECT t::text, r.a
+  FROM remote_tbl r, ROWS FROM (unnest(array[3, 6, 9]),
+                                generate_series(11, 13)) AS t(n, s)
+ WHERE r.a = t.n ORDER BY r.a;
+   t    | a 
+--------+---
+ (3,11) | 3
+ (6,12) | 6
+ (9,13) | 9
+(3 rows)
+
+-- Check whole-row Var represented by function on the nullable
+-- left join side
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT u, ft5.c1, ft5.c2, ft4.c1, ft4.c2 FROM ft5 LEFT JOIN
+(ft4 JOIN unnest(array[1,2], array[3,4]) as u (u1, u2) ON ft4.c1=u1)
+ON ft5.c1 = ft4.c1 WHERE ft5.c1 < 10 ORDER BY ft5.c1;
+                                                                                                                                                                        QUERY PLAN                                                                                                                                                                         
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: u.*, ft5.c1, ft5.c2, ft4.c1, ft4.c2
+   Relations: (public.ft5) LEFT JOIN ((public.ft4) INNER JOIN (ROWS FROM (pg_catalog.unnest(), pg_catalog.unnest()) u))
+   Remote SQL: SELECT CASE WHEN (f3.*)::text IS NOT NULL THEN ROW(f3.c1, f3.c2) END, r1.c1, r1.c2, r2.c1, r2.c2 FROM ("S 1"."T 4" r1 LEFT JOIN ("S 1"."T 3" r2 INNER JOIN ROWS FROM (unnest('{1,2}'::integer[]), unnest('{3,4}'::integer[])) f3(c1, c2) ON (((r2.c1 = f3.c1)))) ON (((r1.c1 = r2.c1)))) WHERE ((r1.c1 < 10)) ORDER BY r1.c1 ASC NULLS LAST
+(4 rows)
+
+SELECT u, ft5.c1, ft5.c2, ft4.c1, ft4.c2 FROM ft5 LEFT JOIN
+(ft4 JOIN unnest(array[1,2], array[3,4]) as u (u1, u2) ON ft4.c1=u1)
+ON ft5.c1 = ft4.c1 WHERE ft5.c1 < 10 ORDER BY ft5.c1;
+ u | c1 | c2 | c1 | c2 
+---+----+----+----+----
+   |  3 |  4 |    |   
+   |  6 |  7 |    |   
+   |  9 | 10 |    |   
+(3 rows)
+
+-- Same nullable-side whole-row Var, but with outer rows that both match
+-- and miss the (foreign x function) inner join.  A multi-column function
+-- RTE is used so that the reference is a genuine whole-row Var (a single
+-- scalar-returning function would collapse to its lone column).  This
+-- exercises the THEN ROW(...) side of deparseColumnRef()'s whole-row CASE
+-- (matched rows reconstruct the composite) as well as the NULL side
+-- (missed rows), confirming the executor rebuilds the anonymous composite
+-- correctly.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT l.a, t FROM remote_tbl l
+  LEFT JOIN (remote_tbl r JOIN unnest(array[2, 4], array[20, 40]) AS t(x, y)
+             ON r.a = t.x)
+  ON l.a = r.a
+ WHERE l.a < 6 ORDER BY l.a;
+                                                                                                                                                                  QUERY PLAN                                                                                                                                                                   
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Foreign Scan
+   Output: l.a, t.*
+   Relations: (public.remote_tbl l) LEFT JOIN ((public.remote_tbl r) INNER JOIN (ROWS FROM (pg_catalog.unnest(), pg_catalog.unnest()) t))
+   Remote SQL: SELECT r1.a, CASE WHEN (f3.*)::text IS NOT NULL THEN ROW(f3.c1, f3.c2) END FROM (public.base_tbl_fn r1 LEFT JOIN (public.base_tbl_fn r2 INNER JOIN ROWS FROM (unnest('{2,4}'::integer[]), unnest('{20,40}'::integer[])) f3(c1, c2) ON (((r2.a = f3.c1)))) ON (((r1.a = r2.a)))) WHERE ((r1.a < 6)) ORDER BY r1.a ASC NULLS LAST
+(4 rows)
+
+SELECT l.a, t FROM remote_tbl l
+  LEFT JOIN (remote_tbl r JOIN unnest(array[2, 4], array[20, 40]) AS t(x, y)
+             ON r.a = t.x)
+  ON l.a = r.a
+ WHERE l.a < 6 ORDER BY l.a;
+ a |   t    
+---+--------
+ 1 | 
+ 2 | (2,20)
+ 3 | 
+ 4 | (4,40)
+ 5 | 
+(5 rows)
+
+RESET enable_hashjoin;
+RESET enable_mergejoin;
+RESET enable_nestloop;
+-- Check foreign join with parameterized function
+CREATE OR REPLACE FUNCTION f(int) RETURNS SETOF int LANGUAGE plpgsql ROWS 10 AS 'BEGIN RETURN QUERY SELECT generate_series(1,$1) ; END' IMMUTABLE;
+ALTER EXTENSION postgres_fdw ADD FUNCTION f(INTEGER);
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH s AS MATERIALIZED (SELECT r1.* FROM remote_tbl r1
+JOIN LATERAL
+(SELECT r2.a FROM remote_tbl r2, f(r1.a) LIMIT 1) s
+ON true)
+SELECT * FROM s ORDER BY 1;
+                                                               QUERY PLAN                                                               
+----------------------------------------------------------------------------------------------------------------------------------------
+ Sort
+   Output: s.a, s.b
+   Sort Key: s.a
+   CTE s
+     ->  Nested Loop
+           Output: r1.a, r1.b
+           ->  Foreign Scan on public.remote_tbl r1
+                 Output: r1.a, r1.b
+                 Remote SQL: SELECT a, b FROM public.base_tbl_fn
+           ->  Foreign Scan
+                 Output: NULL::integer
+                 Relations: (public.remote_tbl r2) INNER JOIN (public.f())
+                 Remote SQL: SELECT NULL FROM (public.base_tbl_fn r1 INNER JOIN public.f($1::integer) f2(c1) ON (TRUE)) LIMIT 1::bigint
+   ->  CTE Scan on s
+         Output: s.a, s.b
+(15 rows)
+
+WITH s AS MATERIALIZED (SELECT r1.* FROM remote_tbl r1
+JOIN LATERAL
+(SELECT r2.a FROM remote_tbl r2, f(r1.a) LIMIT 1) s
+ON true)
+SELECT * FROM s ORDER BY 1;
+ a  |  b  
+----+-----
+  1 | 101
+  2 | 102
+  3 | 103
+  4 | 104
+  5 | 105
+  6 | 106
+  7 | 107
+  8 | 108
+  9 | 109
+ 10 | 110
+ 11 | 111
+ 12 | 112
+ 13 | 113
+ 14 | 114
+ 15 | 115
+ 16 | 116
+ 17 | 117
+ 18 | 118
+ 19 | 119
+ 20 | 120
+ 21 | 121
+ 22 | 122
+ 23 | 123
+ 24 |   7
+ 25 | 125
+ 26 | 126
+ 27 | 127
+ 28 | 128
+ 29 | 129
+ 30 | 130
+(30 rows)
+
+ALTER EXTENSION postgres_fdw DROP FUNCTION f(INTEGER);
+DROP FUNCTION f(INTEGER);
+-- Volatile function in ROWS FROM disqualifies the whole RTE.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT r.a FROM remote_tbl r,
+                ROWS FROM (unnest(array[3, 6, 9]),
+                           generate_series(1, 4 + (random() * 0)::int)) AS t(n, s)
+ WHERE r.a = t.n;
+                                                             QUERY PLAN                                                             
+------------------------------------------------------------------------------------------------------------------------------------
+ Merge Join
+   Output: r.a
+   Merge Cond: (t.n = r.a)
+   ->  Sort
+         Output: t.n
+         Sort Key: t.n
+         ->  Function Scan on t
+               Output: t.n
+               Function Call: unnest('{3,6,9}'::integer[]), generate_series(1, (4 + ((random() * '0'::double precision))::integer))
+   ->  Sort
+         Output: r.a
+         Sort Key: r.a
+         ->  Foreign Scan on public.remote_tbl r
+               Output: r.a
+               Remote SQL: SELECT a FROM public.base_tbl_fn
+(15 rows)
+
+-- LATERAL function referencing a foreign Var: postgres_fdw's
+-- foreign-join pushdown rejects this via the joinrel->lateral_relids
+-- check; the plan is therefore a local NestLoop + FunctionScan.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT r.a, t.x FROM remote_tbl r, LATERAL unnest(array[r.a]) AS t(x)
+WHERE r.a <= 3 ORDER BY r.a;
+                                           QUERY PLAN                                            
+-------------------------------------------------------------------------------------------------
+ Nested Loop
+   Output: r.a, t.x
+   ->  Foreign Scan on public.remote_tbl r
+         Output: r.a, r.b
+         Remote SQL: SELECT a FROM public.base_tbl_fn WHERE ((a <= 3)) ORDER BY a ASC NULLS LAST
+   ->  Function Scan on pg_catalog.unnest t
+         Output: t.x
+         Function Call: unnest(ARRAY[r.a])
+(8 rows)
+
+-- Outer joins with the function RTE are not pushed down (only INNER
+-- joins are supported by function_rte_pushdown_ok()).
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT r.a, t.n FROM remote_tbl r
+     LEFT JOIN unnest(array[1, 2, 3]) AS t(n) ON r.a = t.n
+ WHERE r.a <= 5 ORDER BY r.a;
+                                           QUERY PLAN                                            
+-------------------------------------------------------------------------------------------------
+ Merge Left Join
+   Output: r.a, t.n
+   Merge Cond: (r.a = t.n)
+   ->  Foreign Scan on public.remote_tbl r
+         Output: r.a, r.b
+         Remote SQL: SELECT a FROM public.base_tbl_fn WHERE ((a <= 5)) ORDER BY a ASC NULLS LAST
+   ->  Sort
+         Output: t.n
+         Sort Key: t.n
+         ->  Function Scan on pg_catalog.unnest t
+               Output: t.n
+               Function Call: unnest('{1,2,3}'::integer[])
+(12 rows)
+
+-- SEMI join (EXISTS) with a function RTE is also not pushed down.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT r.a FROM remote_tbl r
+ WHERE EXISTS (SELECT 1 FROM unnest(array[3, 6, 9]) AS t(n) WHERE t.n = r.a)
+ ORDER BY r.a;
+                                   QUERY PLAN                                   
+--------------------------------------------------------------------------------
+ Merge Semi Join
+   Output: r.a
+   Merge Cond: (r.a = t.n)
+   ->  Foreign Scan on public.remote_tbl r
+         Output: r.a, r.b
+         Remote SQL: SELECT a FROM public.base_tbl_fn ORDER BY a ASC NULLS LAST
+   ->  Sort
+         Output: t.n
+         Sort Key: t.n
+         ->  Function Scan on pg_catalog.unnest t
+               Output: t.n
+               Function Call: unnest('{3,6,9}'::integer[])
+(12 rows)
+
+DROP FOREIGN TABLE remote_tbl;
+DROP TABLE base_tbl_fn;
 -- ====================================================================
 -- Check that userid to use when querying the remote table is correctly
 -- propagated into foreign rels present in subqueries under an UNION ALL
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 0ff4ec23164..59af46f6942 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -31,6 +31,7 @@
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
 #include "optimizer/appendinfo.h"
+#include "optimizer/clauses.h"
 #include "optimizer/cost.h"
 #include "optimizer/inherit.h"
 #include "optimizer/optimizer.h"
@@ -88,6 +89,22 @@ enum FdwScanPrivateIndex
 	 * of join, added when the scan is join
 	 */
 	FdwScanPrivateRelations,
+
+	/*
+	 * List of per-RTE function metadata, indexed by base RTI offset.  Each
+	 * element is either NULL (for non-RTE_FUNCTION rels in this scan) or a
+	 * list of three-element lists (funcid, funcrettype, funccollation) -- one
+	 * inner list per function in the RTE.  Allows the executor to rebuild
+	 * TupleDesc entries for whole-row references to function RTEs.
+	 */
+	FdwScanPrivateFunctions,
+
+	/*
+	 * Integer node: minimum base RT index covered by the scan, used to
+	 * translate scan-local indexes to estate-rtable indexes after setrefs.c
+	 * flattens rtables.
+	 */
+	FdwScanPrivateMinRTIndex,
 };
 
 /*
@@ -124,6 +141,11 @@ enum FdwModifyPrivateIndex
  * 2) Boolean flag showing if the remote query has a RETURNING clause
  * 3) Integer list of attribute numbers retrieved by RETURNING, if any
  * 4) Boolean flag showing if we set the command es_processed
+ * 5) Per-RTE function metadata (mirrors FdwScanPrivateFunctions; lets
+ *    the executor rebuild TupleDesc entries for whole-row Vars over
+ *    function RTEs absorbed into a foreign join)
+ * 6) Integer node: minimum base RT index of the scan (mirrors
+ *    FdwScanPrivateMinRTIndex)
  */
 enum FdwDirectModifyPrivateIndex
 {
@@ -135,6 +157,10 @@ enum FdwDirectModifyPrivateIndex
 	FdwDirectModifyPrivateRetrievedAttrs,
 	/* set-processed flag (as a Boolean node) */
 	FdwDirectModifyPrivateSetProcessed,
+	/* Per-RTE function metadata, indexed by base RTI offset */
+	FdwDirectModifyPrivateFunctions,
+	/* Integer node: minimum base RT index in the scan */
+	FdwDirectModifyPrivateMinRTIndex,
 };
 
 /*
@@ -740,6 +766,9 @@ static bool foreign_grouping_ok(PlannerInfo *root, RelOptInfo *grouped_rel,
 static List *get_useful_pathkeys_for_relation(PlannerInfo *root,
 											  RelOptInfo *rel);
 static List *get_useful_ecs_for_relation(PlannerInfo *root, RelOptInfo *rel);
+static Relids get_base_relids(PlannerInfo *root, RelOptInfo *rel);
+static int	get_min_base_rti(PlannerInfo *root, RelOptInfo *rel);
+static List *get_functions_data(PlannerInfo *root, RelOptInfo *rel);
 static void add_paths_with_pathkeys_for_rel(PlannerInfo *root, RelOptInfo *rel,
 											Path *epq_path, List *restrictlist);
 static void add_foreign_grouping_paths(PlannerInfo *root,
@@ -893,7 +922,7 @@ postgresGetForeignRelSize(PlannerInfo *root,
 	 * Identify which baserestrictinfo clauses can be sent to the remote
 	 * server and which can't.
 	 */
-	classifyConditions(root, baserel, baserel->baserestrictinfo,
+	classifyConditions(root, baserel, fpinfo, baserel->baserestrictinfo,
 					   &fpinfo->remote_conds, &fpinfo->local_conds);
 
 	/*
@@ -1297,7 +1326,7 @@ postgresGetForeignPaths(PlannerInfo *root,
 			continue;
 
 		/* See if it is safe to send to remote */
-		if (!is_foreign_expr(root, baserel, rinfo->clause))
+		if (!is_foreign_expr(root, baserel, fpinfo, rinfo->clause))
 			continue;
 
 		/* Calculate required outer rels for the resulting path */
@@ -1373,7 +1402,7 @@ postgresGetForeignPaths(PlannerInfo *root,
 					continue;
 
 				/* See if it is safe to send to remote */
-				if (!is_foreign_expr(root, baserel, rinfo->clause))
+				if (!is_foreign_expr(root, baserel, fpinfo, rinfo->clause))
 					continue;
 
 				/* Calculate required outer rels for the resulting path */
@@ -1513,7 +1542,7 @@ postgresGetForeignPlan(PlannerInfo *root,
 				remote_exprs = lappend(remote_exprs, rinfo->clause);
 			else if (list_member_ptr(fpinfo->local_conds, rinfo))
 				local_exprs = lappend(local_exprs, rinfo->clause);
-			else if (is_foreign_expr(root, foreignrel, rinfo->clause))
+			else if (is_foreign_expr(root, foreignrel, fpinfo, rinfo->clause))
 				remote_exprs = lappend(remote_exprs, rinfo->clause);
 			else
 				local_exprs = lappend(local_exprs, rinfo->clause);
@@ -1634,9 +1663,26 @@ postgresGetForeignPlan(PlannerInfo *root,
 	fdw_private = list_make3(makeString(sql.data),
 							 retrieved_attrs,
 							 makeInteger(fpinfo->fetch_size));
+
+	/*
+	 * Position FdwScanPrivateRelations: either the EXPLAIN relation string
+	 * (joins/upper rels) or a NULL placeholder, so that subsequent indexes
+	 * stay valid for the base-rel scan case.
+	 */
 	if (IS_JOIN_REL(foreignrel) || IS_UPPER_REL(foreignrel))
 		fdw_private = lappend(fdw_private,
 							  makeString(fpinfo->relation_name));
+	else
+		fdw_private = lappend(fdw_private, NULL);
+
+	/*
+	 * FdwScanPrivateFunctions / FdwScanPrivateMinRTIndex carry the metadata
+	 * the executor needs to rebuild TupleDesc entries for whole-row Vars
+	 * pointing at RTE_FUNCTION rels absorbed into the foreign scan.
+	 */
+	fdw_private = lappend(fdw_private, get_functions_data(root, foreignrel));
+	fdw_private = lappend(fdw_private,
+						  makeInteger(get_min_base_rti(root, foreignrel)));
 
 	/*
 	 * Create the ForeignScan node for the given relation.
@@ -1657,9 +1703,15 @@ postgresGetForeignPlan(PlannerInfo *root,
 
 /*
  * Construct a tuple descriptor for the scan tuples handled by a foreign join.
+ *
+ * 'rtfuncdata' is the FdwScanPrivateFunctions list saved at plan time, and
+ * 'rtoffset' is the difference between the executor's RT indexes and the
+ * scan-local RT indexes captured in that list.  Both may be 0/NIL when the
+ * scan has no RTE_FUNCTION dependents.
  */
 static TupleDesc
-get_tupdesc_for_join_scan_tuples(ForeignScanState *node)
+get_tupdesc_for_join_scan_tuples(ForeignScanState *node,
+								 List *rtfuncdata, int rtoffset)
 {
 	ForeignScan *fsplan = (ForeignScan *) node->ss.ps.plan;
 	EState	   *estate = node->ss.ps.state;
@@ -1695,13 +1747,67 @@ get_tupdesc_for_join_scan_tuples(ForeignScanState *node)
 		if (!IsA(var, Var) || var->varattno != 0)
 			continue;
 		rte = list_nth(estate->es_range_table, var->varno - 1);
-		if (rte->rtekind != RTE_RELATION)
-			continue;
-		reltype = get_rel_type_id(rte->relid);
-		if (!OidIsValid(reltype))
-			continue;
-		att->atttypid = reltype;
-		/* shouldn't need to change anything else */
+
+		if (rte->rtekind == RTE_RELATION)
+		{
+			reltype = get_rel_type_id(rte->relid);
+			if (!OidIsValid(reltype))
+				continue;
+			att->atttypid = reltype;
+			/* shouldn't need to change anything else */
+		}
+		else if (rte->rtekind == RTE_FUNCTION)
+		{
+			/*
+			 * A whole-row Var points at a FUNCTION RTE absorbed into the
+			 * foreign join.  Synthesize an anonymous composite TupleDesc from
+			 * the per-function return-type metadata we saved at plan time;
+			 * the deparser emits these as ROW(f<rti>.c1, f<rti>.c2, ...).
+			 *
+			 * For an upperrel scan (the only path that reaches here)
+			 * postgresGetForeignPlan always builds rtfuncdata via
+			 * get_functions_data(), so it is never NIL; the per-RTE slot for
+			 * the function RTE referenced by this Var must likewise be
+			 * populated.
+			 */
+			List	   *funcdata;
+			TupleDesc	rte_tupdesc;
+			int			num_funcs;
+			int			attnum;
+			ListCell   *lc1,
+					   *lc2;
+
+			Assert(rtfuncdata != NIL);
+			funcdata = list_nth(rtfuncdata, var->varno - rtoffset);
+			Assert(funcdata != NIL);
+			num_funcs = list_length(funcdata);
+			Assert(num_funcs == list_length(rte->eref->colnames));
+			rte_tupdesc = CreateTemplateTupleDesc(num_funcs);
+
+			attnum = 1;
+			forboth(lc1, funcdata, lc2, rte->eref->colnames)
+			{
+				List	   *fdata = lfirst_node(List, lc1);
+				char	   *colname = strVal(lfirst(lc2));
+				Oid			funcrettype;
+				Oid			funccollation;
+
+				funcrettype = lsecond_node(Integer, fdata)->ival;
+				funccollation = lthird_node(Integer, fdata)->ival;
+
+				/* get_functions_data() already validated the return type. */
+				Assert(OidIsValid(funcrettype) && funcrettype != RECORDOID);
+
+				TupleDescInitEntry(rte_tupdesc, (AttrNumber) attnum, colname,
+								   funcrettype, -1, 0);
+				TupleDescInitEntryCollation(rte_tupdesc, (AttrNumber) attnum,
+											funccollation);
+				attnum++;
+			}
+
+			assign_record_type_typmod(rte_tupdesc);
+			att->atttypmod = rte_tupdesc->tdtypmod;
+		}
 	}
 	return tupdesc;
 }
@@ -1737,14 +1843,30 @@ postgresBeginForeignScan(ForeignScanState *node, int eflags)
 
 	/*
 	 * Identify which user to do the remote access as.  This should match what
-	 * ExecCheckPermissions() does.
+	 * ExecCheckPermissions() does.  For a join, scan the base relids until we
+	 * find an RTE_RELATION (the foreign-table side); ignore any RTE_FUNCTION
+	 * absorbed into the join, which contributes no relation OID to look up.
 	 */
 	userid = OidIsValid(fsplan->checkAsUser) ? fsplan->checkAsUser : GetUserId();
+	rte = NULL;
 	if (fsplan->scan.scanrelid > 0)
+	{
 		rtindex = fsplan->scan.scanrelid;
+		rte = exec_rt_fetch(rtindex, estate);
+	}
 	else
-		rtindex = bms_next_member(fsplan->fs_base_relids, -1);
-	rte = exec_rt_fetch(rtindex, estate);
+	{
+		rtindex = -1;
+		while ((rtindex = bms_next_member(fsplan->fs_base_relids, rtindex)) >= 0)
+		{
+			rte = exec_rt_fetch(rtindex, estate);
+			if (rte != NULL && rte->rtekind == RTE_RELATION)
+				break;
+			rte = NULL;
+		}
+		if (rte == NULL)
+			elog(ERROR, "could not locate a foreign relation RTE in foreign scan");
+	}
 
 	/* Get info about foreign table. */
 	table = GetForeignTable(rte->relid);
@@ -1787,8 +1909,19 @@ postgresBeginForeignScan(ForeignScanState *node, int eflags)
 	}
 	else
 	{
+		List	   *rtfuncdata = (List *) list_nth(fsplan->fdw_private,
+												   FdwScanPrivateFunctions);
+		int			min_base_rti = intVal(list_nth(fsplan->fdw_private,
+												   FdwScanPrivateMinRTIndex));
+		int			rtoffset = bms_next_member(fsplan->fs_base_relids, -1) -
+			min_base_rti;
+
+		Assert(min_base_rti > 0);
+		Assert(rtoffset >= 0);
+
 		fsstate->rel = NULL;
-		fsstate->tupdesc = get_tupdesc_for_join_scan_tuples(node);
+		fsstate->tupdesc = get_tupdesc_for_join_scan_tuples(node, rtfuncdata,
+															rtoffset);
 	}
 
 	fsstate->attinmeta = TupleDescGetAttInMetadata(fsstate->tupdesc);
@@ -2741,7 +2874,7 @@ postgresPlanDirectModify(PlannerInfo *root,
 			if (attno <= InvalidAttrNumber) /* shouldn't happen */
 				elog(ERROR, "system-column update is not supported");
 
-			if (!is_foreign_expr(root, foreignrel, (Expr *) tle->expr))
+			if (!is_foreign_expr(root, foreignrel, fpinfo, (Expr *) tle->expr))
 				return false;
 		}
 	}
@@ -2828,6 +2961,10 @@ postgresPlanDirectModify(PlannerInfo *root,
 									makeBoolean((retrieved_attrs != NIL)),
 									retrieved_attrs,
 									makeBoolean(plan->canSetTag));
+	fscan->fdw_private = lappend(fscan->fdw_private,
+								 get_functions_data(root, foreignrel));
+	fscan->fdw_private = lappend(fscan->fdw_private,
+								 makeInteger(get_min_base_rti(root, foreignrel)));
 
 	/*
 	 * Update the foreign-join-related fields.
@@ -2941,7 +3078,26 @@ postgresBeginDirectModify(ForeignScanState *node, int eflags)
 		TupleDesc	tupdesc;
 
 		if (fsplan->scan.scanrelid == 0)
-			tupdesc = get_tupdesc_for_join_scan_tuples(node);
+		{
+			/*
+			 * DirectModify on a foreign join: use the per-RTE function
+			 * metadata saved at plan time so a whole-row Var pointing at a
+			 * function RTE absorbed into the join can be rebuilt into a
+			 * usable TupleDesc (e.g. RETURNING t for a join with UNNEST(...,
+			 * ...) AS t(bx, i)).
+			 */
+			List	   *rtfuncdata = (List *) list_nth(fsplan->fdw_private,
+													   FdwDirectModifyPrivateFunctions);
+			int			min_base_rti = intVal(list_nth(fsplan->fdw_private,
+													   FdwDirectModifyPrivateMinRTIndex));
+			int			rtoffset = bms_next_member(fsplan->fs_base_relids, -1) -
+				min_base_rti;
+
+			Assert(min_base_rti > 0);
+			Assert(rtoffset >= 0);
+
+			tupdesc = get_tupdesc_for_join_scan_tuples(node, rtfuncdata, rtoffset);
+		}
 		else
 			tupdesc = RelationGetDescr(dmstate->rel);
 
@@ -3054,7 +3210,8 @@ postgresExplainForeignScan(ForeignScanState *node, ExplainState *es)
 	 * We do that here, not when the plan is created, because we can't know
 	 * what aliases ruleutils.c will assign at plan creation time.
 	 */
-	if (list_length(fdw_private) > FdwScanPrivateRelations)
+	if (list_length(fdw_private) > FdwScanPrivateRelations &&
+		list_nth(fdw_private, FdwScanPrivateRelations) != NULL)
 	{
 		StringInfoData relations;
 		char	   *rawrelations;
@@ -3104,25 +3261,90 @@ postgresExplainForeignScan(ForeignScanState *node, ExplainState *es)
 				rti += rtoffset;
 				Assert(bms_is_member(rti, plan->fs_base_relids));
 				rte = rt_fetch(rti, es->rtable);
-				Assert(rte->rtekind == RTE_RELATION);
-				/* This logic should agree with explain.c's ExplainTargetRel */
-				relname = get_rel_name(rte->relid);
-				if (es->verbose)
-				{
-					char	   *namespace;
 
-					namespace = get_namespace_name_or_temp(get_rel_namespace(rte->relid));
-					appendStringInfo(&relations, "%s.%s",
-									 quote_identifier(namespace),
-									 quote_identifier(relname));
+				if (rte->rtekind == RTE_FUNCTION)
+				{
+					List	   *rtfuncdata = list_nth(fdw_private, FdwScanPrivateFunctions);
+					List	   *funcdata;
+					bool		multi_func;
+					bool		first = true;
+					ListCell   *lc;
+
+					funcdata = list_nth(rtfuncdata, rti - rtoffset);
+
+					multi_func = list_length(funcdata) > 1;
+
+					if (multi_func)
+						appendStringInfoString(&relations, "ROWS FROM (");
+
+					foreach(lc, funcdata)
+					{
+						List	   *funcinfo;
+						Oid			funcid;
+
+
+						if (!first)
+							appendStringInfoString(&relations, ", ");
+
+						funcinfo = (List *) lfirst(lc);
+
+						funcid = linitial_node(Integer, funcinfo)->ival;
+						/* Checked by function_rte_pushdown_ok() */
+						Assert(OidIsValid(funcid));
+
+						/* Match RTE_RELATION behavior */
+						relname = get_func_name(funcid);
+						if (relname == NULL)
+							elog(ERROR, "cache lookup failed for function %u", funcid);
+						if (es->verbose)
+						{
+							char	   *namespace;
+							Oid			nsoid = get_func_namespace(funcid);
+
+							namespace = get_namespace_name(nsoid);
+							if (namespace == NULL)
+								elog(ERROR, "cache lookup failed for namespace %u", nsoid);
+
+							appendStringInfo(&relations, "%s.%s()",
+											 quote_identifier(namespace),
+											 quote_identifier(relname));
+						}
+						else
+							appendStringInfo(&relations, "%s()", quote_identifier(relname));
+
+						first = false;
+					}
+					/* Close ROWS FROM */
+					if (multi_func)
+						appendStringInfoChar(&relations, ')');
 				}
 				else
-					appendStringInfoString(&relations,
-										   quote_identifier(relname));
+				{
+					Assert(rte->rtekind == RTE_RELATION);
+
+					/*
+					 * This logic should agree with explain.c's
+					 * ExplainTargetRel
+					 */
+					relname = get_rel_name(rte->relid);
+					if (es->verbose)
+					{
+						char	   *namespace;
+
+						namespace = get_namespace_name_or_temp(get_rel_namespace(rte->relid));
+						appendStringInfo(&relations, "%s.%s",
+										 quote_identifier(namespace),
+										 quote_identifier(relname));
+					}
+					else
+						appendStringInfoString(&relations,
+											   quote_identifier(relname));
+				}
+
 				refname = (char *) list_nth(es->rtable_names, rti - 1);
 				if (refname == NULL)
 					refname = rte->eref->aliasname;
-				if (strcmp(refname, relname) != 0)
+				if (relname == NULL || strcmp(refname, relname) != 0)
 					appendStringInfo(&relations, " %s",
 									 quote_identifier(refname));
 			}
@@ -3346,7 +3568,7 @@ estimate_path_cost_size(PlannerInfo *root,
 		 * param_join_conds might contain both clauses that are safe to send
 		 * across, and clauses that aren't.
 		 */
-		classifyConditions(root, foreignrel, param_join_conds,
+		classifyConditions(root, foreignrel, fpinfo, param_join_conds,
 						   &remote_param_join_conds, &local_param_join_conds);
 
 		/* Build the list of columns to be fetched from the foreign server. */
@@ -3479,8 +3701,17 @@ estimate_path_cost_size(PlannerInfo *root,
 			/* For join we expect inner and outer relations set */
 			Assert(fpinfo->innerrel && fpinfo->outerrel);
 
-			fpinfo_i = (PgFdwRelationInfo *) fpinfo->innerrel->fdw_private;
-			fpinfo_o = (PgFdwRelationInfo *) fpinfo->outerrel->fdw_private;
+			/*
+			 * For a FUNCTION RTE absorbed into the join, use the stub fpinfo
+			 * we built in foreign_join_ok(), since the function rel itself
+			 * has no fdw_private.
+			 */
+			fpinfo_i = fpinfo->inner_func_fpinfo ?
+				fpinfo->inner_func_fpinfo :
+				(PgFdwRelationInfo *) fpinfo->innerrel->fdw_private;
+			fpinfo_o = fpinfo->outer_func_fpinfo ?
+				fpinfo->outer_func_fpinfo :
+				(PgFdwRelationInfo *) fpinfo->outerrel->fdw_private;
 
 			/* Estimate of number of rows in cross product */
 			nrows = fpinfo_i->rows * fpinfo_o->rows;
@@ -6619,6 +6850,205 @@ semijoin_target_ok(PlannerInfo *root, RelOptInfo *joinrel, RelOptInfo *outerrel,
 	return ok;
 }
 
+/*
+ * get_base_relids
+ *		Return the set of base relids referenced by a foreign scan rel.
+ *
+ * For an upper rel we use the all-query relids minus the outer joins;
+ * otherwise the rel's own relids minus the outer joins.  The result matches
+ * the relids that create_foreignscan_plan() ultimately uses for
+ * ForeignScan.fs_base_relids, so it is suitable for any tagging we want to
+ * store via plan-private state.
+ */
+static Relids
+get_base_relids(PlannerInfo *root, RelOptInfo *rel)
+{
+	Relids		relids;
+
+	if (rel->reloptkind == RELOPT_UPPER_REL)
+		relids = root->all_query_rels;
+	else
+		relids = rel->relids;
+
+	return bms_difference(relids, root->outer_join_rels);
+}
+
+/*
+ * get_min_base_rti
+ *		Lowest base RT index in the foreign scan rel.
+ *
+ * After setrefs.c flattens the rtable, the scan-local indexes saved in
+ * plan-private data can be translated to estate indexes by adding
+ * (ForeignScan.fs_base_relids min - this value).  Captured at plan time
+ * because create_foreignscan_plan() computes the same value internally.
+ */
+static int
+get_min_base_rti(PlannerInfo *root, RelOptInfo *rel)
+{
+	Relids		relids = get_base_relids(root, rel);
+
+	return bms_next_member(relids, -1);
+}
+
+/*
+ * get_functions_data
+ *		Build the per-RTE function metadata list saved as
+ *		FdwScanPrivateFunctions.
+ *
+ * The result list is indexed by base RT index relative to the lowest base
+ * RT index of the scan.  Each element is either NULL (for non-RTE_FUNCTION
+ * base rels in this scan) or a List of List of two Integer nodes:
+ * (funcrettype, funccollation) -- one inner list per RangeTblFunction.
+ *
+ * Only RTE_FUNCTION relids actually appearing in the foreign scan's
+ * fs_base_relids contribute; others are placeholders so that the consumer
+ * can index into the result by RTI offset.
+ */
+static List *
+get_functions_data(PlannerInfo *root, RelOptInfo *rel)
+{
+	List	   *rtfuncdata = NIL;
+	Relids		fscan_relids = get_base_relids(root, rel);
+	int			i;
+
+	for (i = 0; i < root->simple_rel_array_size; i++)
+	{
+		RangeTblEntry *rte = root->simple_rte_array[i];
+		List	   *funcdata = NIL;
+		ListCell   *lc;
+
+		if (rte == NULL || i == 0 ||
+			!bms_is_member(i, fscan_relids) ||
+			rte->rtekind != RTE_FUNCTION)
+		{
+			rtfuncdata = lappend(rtfuncdata, NULL);
+			continue;
+		}
+
+		foreach(lc, rte->functions)
+		{
+			RangeTblFunction *rtfunc = (RangeTblFunction *) lfirst(lc);
+			Oid			funcrettype;
+			Oid			funccollation;
+			TupleDesc	tupdesc;
+			Oid			funcid;
+
+			get_expr_result_type(rtfunc->funcexpr, &funcrettype, &tupdesc);
+
+			/*
+			 * function_rte_pushdown_ok() already rejected any function that
+			 * doesn't return a well-defined scalar type, so this is a mere
+			 * cross-check.
+			 */
+			Assert(OidIsValid(funcrettype) && funcrettype != RECORDOID);
+
+			funccollation = exprCollation(rtfunc->funcexpr);
+
+			funcid = ((FuncExpr *) rtfunc->funcexpr)->funcid;
+
+			funcdata = lappend(funcdata,
+							   list_make3(makeInteger(funcid),
+										  makeInteger(funcrettype),
+										  makeInteger(funccollation)));
+		}
+
+		rtfuncdata = lappend(rtfuncdata, funcdata);
+	}
+
+	return rtfuncdata;
+}
+
+/*
+ * Check if a relation is a FUNCTION RTE that can be absorbed into a remote
+ * join.  Every function in the RTE must
+ *
+ *   - return a well-defined scalar type -- we don't ship records/composite
+ *     since the remote server cannot reconstruct a column definition list
+ *     and our deparser does not emit one;
+ *   - have a shippable expression with no mutable subnodes -- is_foreign_expr()
+ *     rejects volatile/stable functions through contain_mutable_functions(),
+ *     so the IMMUTABLE-only restriction is implicit;
+ *   - not contain SubPlans -- we'd otherwise need to ship sub-results to
+ *     the remote, which we do not implement.
+ *
+ * WITH ORDINALITY is not supported yet.
+ */
+static bool
+function_rte_pushdown_ok(PlannerInfo *root, RelOptInfo *rel,
+						 RelOptInfo *fdwrel)
+{
+	RangeTblEntry *rte;
+	ListCell   *lc;
+
+	if (rel->rtekind != RTE_FUNCTION)
+		return false;
+	rte = planner_rt_fetch(rel->relid, root);
+
+	/*
+	 * build_simple_rel() copies rtekind straight from the RTE, so for a base
+	 * rel rel->rtekind always matches the RTE's; the check above is therefore
+	 * sufficient.
+	 */
+	Assert(rte->rtekind == RTE_FUNCTION);
+
+	if (rte->funcordinality)
+		return false;
+
+	/*
+	 * Reject up-front any function RTE that lateral-references another
+	 * relation: foreign-join push-down would need to parameterise the remote
+	 * query per outer row, which we don't support, and even considering the
+	 * path is expensive on the planner side.  The surrounding lateral_relids
+	 * check in postgresGetForeignJoinPaths() would normally bail out for the
+	 * joinrel, but doing the check here avoids walking the function
+	 * expression entirely.
+	 *
+	 * Note this rejects only lateral references to another relation at the
+	 * same query level.  A function argument referencing an outer query level
+	 * (e.g. f(outer.col) inside a subquery) is a different case: it becomes a
+	 * PARAM_EXEC Param, the function rel's lateral_relids is empty, and
+	 * foreign_expr_walker() intentionally treats PARAM_EXEC as shippable. The
+	 * remote query then carries a parameter placeholder, and postgres_fdw's
+	 * ordinary parameter machinery re-sends it on each rescan -- i.e. it
+	 * works as a normal parameterized foreign scan, which is fine.
+	 */
+	if (!bms_is_empty(rel->lateral_relids))
+		return false;
+
+	Assert(list_length(rte->functions) >= 1);
+
+	foreach(lc, rte->functions)
+	{
+		RangeTblFunction *rtfunc = (RangeTblFunction *) lfirst(lc);
+		TypeFuncClass functypclass;
+		Oid			funcrettype;
+		TupleDesc	tupdesc;
+
+		/* Refuse to deal with strange funcexprs */
+		if (!IsA(rtfunc->funcexpr, FuncExpr))
+			return false;
+
+		if (!OidIsValid(((FuncExpr *) rtfunc->funcexpr)->funcid))
+			return false;
+
+		functypclass = get_expr_result_type(rtfunc->funcexpr,
+											&funcrettype, &tupdesc);
+		if (functypclass != TYPEFUNC_SCALAR)
+			return false;
+		if (!OidIsValid(funcrettype) ||
+			funcrettype == RECORDOID ||
+			funcrettype == VOIDOID)
+			return false;
+
+		if (contain_subplans(rtfunc->funcexpr))
+			return false;
+		if (!is_foreign_expr(root, fdwrel, fdwrel->fdw_private, (Expr *) rtfunc->funcexpr))
+			return false;
+	}
+
+	return true;
+}
+
 /*
  * Assess whether the join between inner and outer relations can be pushed down
  * to the foreign server. As a side effect, save information we obtain in this
@@ -6634,6 +7064,8 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	PgFdwRelationInfo *fpinfo_i;
 	ListCell   *lc;
 	List	   *joinclauses;
+	bool		outer_is_function = false;
+	bool		inner_is_function = false;
 
 	/*
 	 * We support pushing down INNER, LEFT, RIGHT, FULL OUTER and SEMI joins.
@@ -6652,15 +7084,86 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 		return false;
 
 	/*
-	 * If either of the joining relations is marked as unsafe to pushdown, the
-	 * join can not be pushed down.
+	 * Detect mixed (foreign x function-RTE) cases.  Only INNER joins are
+	 * supported initially.  We dispatch on rtekind here so that the same
+	 * function RTE can be absorbed into joins on multiple foreign servers
+	 * (each call gets its own stub fpinfo and rechecks shippability for the
+	 * specific server).
 	 */
 	fpinfo = (PgFdwRelationInfo *) joinrel->fdw_private;
-	fpinfo_o = (PgFdwRelationInfo *) outerrel->fdw_private;
-	fpinfo_i = (PgFdwRelationInfo *) innerrel->fdw_private;
-	if (!fpinfo_o || !fpinfo_o->pushdown_safe ||
-		!fpinfo_i || !fpinfo_i->pushdown_safe)
-		return false;
+	if (jointype == JOIN_INNER && innerrel->rtekind == RTE_FUNCTION &&
+		(fpinfo_o = (PgFdwRelationInfo *) outerrel->fdw_private) &&
+		fpinfo_o->pushdown_safe &&
+		function_rte_pushdown_ok(root, innerrel, outerrel))
+	{
+		inner_is_function = true;
+	}
+	else if (jointype == JOIN_INNER && outerrel->rtekind == RTE_FUNCTION &&
+			 (fpinfo_i = (PgFdwRelationInfo *) innerrel->fdw_private) &&
+			 fpinfo_i->pushdown_safe &&
+			 function_rte_pushdown_ok(root, outerrel, innerrel))
+	{
+		outer_is_function = true;
+	}
+	else
+	{
+		fpinfo_o = (PgFdwRelationInfo *) outerrel->fdw_private;
+		fpinfo_i = (PgFdwRelationInfo *) innerrel->fdw_private;
+		if (!fpinfo_o || !fpinfo_o->pushdown_safe ||
+			!fpinfo_i || !fpinfo_i->pushdown_safe)
+			return false;
+	}
+
+	/*
+	 * If one side is a function RTE, allocate a stub fpinfo so the rest of
+	 * this function and the cost estimator can treat it uniformly.  We hand
+	 * the stub to the joinrel's deparser via the same path the foreign side
+	 * uses, but we never permanently attach it to the function rel's
+	 * fdw_private (different joinrels may pair the same function RTE with
+	 * different foreign servers).
+	 */
+	if (inner_is_function)
+	{
+		fpinfo_i = palloc0_object(PgFdwRelationInfo);
+		fpinfo_i->pushdown_safe = true;
+		fpinfo_i->server = fpinfo_o->server;
+		fpinfo_i->shippable_extensions = fpinfo_o->shippable_extensions;
+		fpinfo_i->relation_name = psprintf("%u", innerrel->relid);
+		fpinfo_i->rows = innerrel->rows;
+		fpinfo_i->width = innerrel->reltarget->width;
+		fpinfo_i->retrieved_rows = innerrel->rows;
+		fpinfo_i->rel_startup_cost = 0;
+		fpinfo_i->rel_total_cost = 0;
+
+		/*
+		 * Classify the function rel's own baserestrictinfo now, so that the
+		 * local_conds check below can bail out if any of it is unshippable.
+		 * We classify against the stub, not the joinrel's fpinfo, because the
+		 * latter's server/shippable_extensions aren't populated until
+		 * merge_fdw_options() runs further down.
+		 */
+		classifyConditions(root, innerrel, fpinfo_i, innerrel->baserestrictinfo,
+						   &fpinfo_i->remote_conds, &fpinfo_i->local_conds);
+		fpinfo->inner_func_fpinfo = fpinfo_i;
+	}
+	else if (outer_is_function)
+	{
+		fpinfo_o = palloc0_object(PgFdwRelationInfo);
+		fpinfo_o->pushdown_safe = true;
+		fpinfo_o->server = fpinfo_i->server;
+		fpinfo_o->shippable_extensions = fpinfo_i->shippable_extensions;
+		fpinfo_o->relation_name = psprintf("%u", outerrel->relid);
+		fpinfo_o->rows = outerrel->rows;
+		fpinfo_o->width = outerrel->reltarget->width;
+		fpinfo_o->retrieved_rows = outerrel->rows;
+		fpinfo_o->rel_startup_cost = 0;
+		fpinfo_o->rel_total_cost = 0;
+
+		/* See the comment in the inner_is_function branch above. */
+		classifyConditions(root, outerrel, fpinfo_o, outerrel->baserestrictinfo,
+						   &fpinfo_o->remote_conds, &fpinfo_o->local_conds);
+		fpinfo->outer_func_fpinfo = fpinfo_o;
+	}
 
 	/*
 	 * If joining relations have local conditions, those conditions are
@@ -6698,7 +7201,7 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	foreach(lc, extra->restrictlist)
 	{
 		RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);
-		bool		is_remote_clause = is_foreign_expr(root, joinrel,
+		bool		is_remote_clause = is_foreign_expr(root, joinrel, fpinfo,
 													   rinfo->clause);
 
 		if (IS_OUTER_JOIN(jointype) &&
@@ -7396,7 +7899,7 @@ foreign_grouping_ok(PlannerInfo *root, RelOptInfo *grouped_rel,
 			 * If any GROUP BY expression is not shippable, then we cannot
 			 * push down aggregation to the foreign server.
 			 */
-			if (!is_foreign_expr(root, grouped_rel, expr))
+			if (!is_foreign_expr(root, grouped_rel, fpinfo, expr))
 				return false;
 
 			/*
@@ -7424,7 +7927,7 @@ foreign_grouping_ok(PlannerInfo *root, RelOptInfo *grouped_rel,
 			 * Non-grouping expression we need to compute.  Can we ship it
 			 * as-is to the foreign server?
 			 */
-			if (is_foreign_expr(root, grouped_rel, expr) &&
+			if (is_foreign_expr(root, grouped_rel, fpinfo, expr) &&
 				!is_foreign_param(root, grouped_rel, expr))
 			{
 				/* Yes, so add to tlist as-is; OK to suppress duplicates */
@@ -7444,7 +7947,7 @@ foreign_grouping_ok(PlannerInfo *root, RelOptInfo *grouped_rel,
 				 * don't have to check is_foreign_param, since that certainly
 				 * won't return true for any such expression.)
 				 */
-				if (!is_foreign_expr(root, grouped_rel, (Expr *) aggvars))
+				if (!is_foreign_expr(root, grouped_rel, fpinfo, (Expr *) aggvars))
 					return false;
 
 				/*
@@ -7496,7 +7999,7 @@ foreign_grouping_ok(PlannerInfo *root, RelOptInfo *grouped_rel,
 									  grouped_rel->relids,
 									  NULL,
 									  NULL);
-			if (is_foreign_expr(root, grouped_rel, expr))
+			if (is_foreign_expr(root, grouped_rel, fpinfo, expr))
 				fpinfo->remote_conds = lappend(fpinfo->remote_conds, rinfo);
 			else
 				fpinfo->local_conds = lappend(fpinfo->local_conds, rinfo);
@@ -7533,7 +8036,7 @@ foreign_grouping_ok(PlannerInfo *root, RelOptInfo *grouped_rel,
 			 */
 			if (IsA(expr, Aggref))
 			{
-				if (!is_foreign_expr(root, grouped_rel, expr))
+				if (!is_foreign_expr(root, grouped_rel, fpinfo, expr))
 					return false;
 
 				tlist = add_to_flat_tlist(tlist, list_make1(expr));
@@ -8046,8 +8549,8 @@ add_foreign_final_paths(PlannerInfo *root, RelOptInfo *input_rel,
 	 * Also, the LIMIT/OFFSET cannot be pushed down, if their expressions are
 	 * not safe to remote.
 	 */
-	if (!is_foreign_expr(root, input_rel, (Expr *) parse->limitOffset) ||
-		!is_foreign_expr(root, input_rel, (Expr *) parse->limitCount))
+	if (!is_foreign_expr(root, input_rel, ifpinfo, (Expr *) parse->limitOffset) ||
+		!is_foreign_expr(root, input_rel, ifpinfo, (Expr *) parse->limitCount))
 		return;
 
 	/* Safe to push down */
@@ -8693,7 +9196,7 @@ find_em_for_rel(PlannerInfo *root, EquivalenceClass *ec, RelOptInfo *rel)
 		if (bms_is_subset(em->em_relids, rel->relids) &&
 			!bms_is_empty(em->em_relids) &&
 			bms_is_empty(bms_intersect(em->em_relids, fpinfo->hidden_subquery_rels)) &&
-			is_foreign_expr(root, rel, em->em_expr))
+			is_foreign_expr(root, rel, fpinfo, em->em_expr))
 			return em;
 	}
 
@@ -8715,6 +9218,7 @@ EquivalenceMember *
 find_em_for_rel_target(PlannerInfo *root, EquivalenceClass *ec,
 					   RelOptInfo *rel)
 {
+	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
 	PathTarget *target = rel->reltarget;
 	ListCell   *lc1;
 	int			i;
@@ -8764,7 +9268,7 @@ find_em_for_rel_target(PlannerInfo *root, EquivalenceClass *ec,
 				continue;
 
 			/* Check that expression (including relabels!) is shippable */
-			if (is_foreign_expr(root, rel, em->em_expr))
+			if (is_foreign_expr(root, rel, fpinfo, em->em_expr))
 				return em;
 		}
 
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index a2bb1ff352c..da7da1c2ea9 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -106,6 +106,16 @@ typedef struct PgFdwRelationInfo
 	/* joinclauses contains only JOIN/ON conditions for an outer join */
 	List	   *joinclauses;	/* List of RestrictInfo */
 
+	/*
+	 * If a FUNCTION RTE was absorbed into this join, these point at the stub
+	 * PgFdwRelationInfo for the function side (paired with the
+	 * outerrel/innerrel), so the cost estimator and deparser can find it
+	 * without consulting the function rel's fdw_private.  At most one of
+	 * outer_func_fpinfo/inner_func_fpinfo is set.
+	 */
+	struct PgFdwRelationInfo *outer_func_fpinfo;
+	struct PgFdwRelationInfo *inner_func_fpinfo;
+
 	/* Upper relation information */
 	UpperRelationKind stage;
 
@@ -183,11 +193,13 @@ extern char *pgfdw_application_name;
 /* in deparse.c */
 extern void classifyConditions(PlannerInfo *root,
 							   RelOptInfo *baserel,
+							   PgFdwRelationInfo *fpinfo,
 							   List *input_conds,
 							   List **remote_conds,
 							   List **local_conds);
 extern bool is_foreign_expr(PlannerInfo *root,
 							RelOptInfo *baserel,
+							PgFdwRelationInfo *fpinfo,
 							Expr *expr);
 extern bool is_foreign_param(PlannerInfo *root,
 							 RelOptInfo *baserel,
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 267d3c1a7e7..2e63281ce2d 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -790,6 +790,271 @@ SELECT t1.c1, t2.c2 FROM v4 t1 LEFT JOIN ft5 t2 ON (t1.c1 = t2.c1) ORDER BY t1.c
 SELECT t1.c1, t2.c2 FROM v4 t1 LEFT JOIN ft5 t2 ON (t1.c1 = t2.c1) ORDER BY t1.c1, t2.c1 OFFSET 10 LIMIT 10;
 ALTER VIEW v4 OWNER TO regress_view_owner;
 
+-- ===================================================================
+-- Foreign-join with FUNCTION RTE pushdown (IMMUTABLE functions only)
+-- ===================================================================
+-- IMMUTABLE function: unnest of constant array can be pushed down
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1, t1.c3 FROM ft1 t1, unnest(ARRAY[1, 5, 10, 100]::int[]) AS u(id)
+WHERE t1.c1 = u.id ORDER BY t1.c1;
+SELECT t1.c1, t1.c3 FROM ft1 t1, unnest(ARRAY[1, 5, 10, 100]::int[]) AS u(id)
+WHERE t1.c1 = u.id ORDER BY t1.c1;
+
+-- IMMUTABLE function: generate_series with constant args
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1 FROM ft1 t1, generate_series(1, 4) AS g(id)
+WHERE t1.c1 = g.id ORDER BY t1.c1;
+SELECT t1.c1 FROM ft1 t1, generate_series(1, 4) AS g(id)
+WHERE t1.c1 = g.id ORDER BY t1.c1;
+
+-- VOLATILE function (random) must NOT be pushed down
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1 FROM ft1 t1, generate_series(1, 4 + (random() * 0)::int) AS g(id)
+WHERE t1.c1 = g.id;
+
+-- WITH ORDINALITY must NOT be pushed down (limitation of this implementation)
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1, u.ord
+FROM ft1 t1, unnest(ARRAY[1, 5, 10]::int[]) WITH ORDINALITY AS u(id, ord)
+WHERE t1.c1 = u.id;
+
+-- Same function RTE joined with two different foreign servers: planner picks
+-- one absorption + a local join with the second foreign server.  The fact
+-- that the function is IMMUTABLE makes this safe even if both sides chose to
+-- absorb it independently.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1, t2.c1
+FROM ft1 t1, ft6 t2, unnest(ARRAY[1, 5, 10, 100]::int[]) AS u(id)
+WHERE t1.c1 = u.id AND t2.c1 = u.id ORDER BY t1.c1;
+
+-- Cost-based selection between two foreign servers: ft1 ("S 1"."T 1") has
+-- 1000 rows, ft6 ("S 1"."T 4") has ~33 rows.  The same query shape gets a
+-- different push-down target depending on a predicate that changes the
+-- effective cardinality of one side -- the function "jumps" to whichever
+-- foreign scan benefits more from being pre-filtered.
+ANALYZE ft1;
+ANALYZE ft6;
+-- No extra predicate: ft1 is the bigger side, function absorbed there.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1, t2.c1
+FROM ft1 t1, ft6 t2, unnest(ARRAY[3, 6, 9, 12, 15, 18]::int[]) AS u(id)
+WHERE t1.c1 = u.id AND t2.c1 = u.id;
+-- Selective predicate on ft1.c3 (not in the eqclass) shrinks ft1 to a
+-- handful of remote rows; now ft6 is effectively the bigger side and the
+-- function is absorbed into ft6 instead.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1, t2.c1
+FROM ft1 t1, ft6 t2, unnest(ARRAY[3, 6, 9, 12, 15, 18]::int[]) AS u(id)
+WHERE t1.c1 = u.id AND t2.c1 = u.id AND t1.c3 < '00010';
+
+-- The remaining scenarios reuse a dedicated foreign table to cover the
+-- corner cases of FUNCTION RTE push-down: function-first FROM, record
+-- return type rejection, whole-row reference, UPDATE...FROM..., and
+-- multi-function ROWS FROM.
+CREATE TABLE base_tbl_fn (a int, b int);
+INSERT INTO base_tbl_fn
+  SELECT g, g + 100 FROM generate_series(1, 30) g;
+CREATE FOREIGN TABLE remote_tbl (a int, b int)
+  SERVER loopback OPTIONS (table_name 'base_tbl_fn');
+
+-- The function RTE appears first in FROM; the foreign relation must be
+-- found by scanning fs_base_relids for an RTE_RELATION rather than
+-- using scan->fs_relid blindly.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r WHERE r.a = n;
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r
+WHERE r.a = n ORDER BY r.a;
+
+-- Function RTE is restricted, shippable conditions
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r WHERE r.a = n and n > 3;
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r
+WHERE r.a = n and n > 3 ORDER BY r.a;
+
+-- Function RTE is restricted, nonshippable conditions
+CREATE FUNCTION f_local(int) RETURNS int AS $$
+BEGIN
+RETURN $1;
+END
+$$ LANGUAGE plpgsql;
+
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r WHERE r.a = n and n > f_local(3);
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r
+WHERE r.a = n and n > f_local(3) ORDER BY r.a;
+
+DROP FUNCTION f_local(int);
+
+-- Check that a qual on the function RTE using a function from a shippable
+-- extension is pushed down.  plpgsql (not inlined) with the column as
+-- argument (not const-folded) keeps the function call in the qual.
+CREATE FUNCTION f_ext(int) RETURNS int AS $$
+BEGIN RETURN $1; END
+$$ LANGUAGE plpgsql IMMUTABLE;
+ALTER EXTENSION postgres_fdw ADD FUNCTION f_ext(int);
+-- Force pushdown so the fixed-code plan is deterministically a Foreign
+-- Scan; on the unfixed code the qual is classified local, the join is
+-- refused, and the plan falls back to a local join instead.
+SET enable_hashjoin = off;
+SET enable_mergejoin = off;
+SET enable_nestloop = off;
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r WHERE r.a = n and f_ext(n) > 3;
+SELECT * FROM unnest(array[2, 3, 4]) n, remote_tbl r
+WHERE r.a = n and f_ext(n) > 3 ORDER BY r.a;
+RESET enable_hashjoin;
+RESET enable_mergejoin;
+RESET enable_nestloop;
+ALTER EXTENSION postgres_fdw DROP FUNCTION f_ext(int);
+DROP FUNCTION f_ext(int);
+
+-- A function returning record (composite) is forbidden; pushing it
+-- would yield a remote "column definition list is required" error.
+-- function_rte_pushdown_ok() rejects it via TYPEFUNC_SCALAR.
+CREATE OR REPLACE FUNCTION f_ret_record() RETURNS record AS $$
+  SELECT (1, 2)::record
+$$ LANGUAGE SQL IMMUTABLE;
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT s FROM remote_tbl rt, f_ret_record() AS s(a int, b int)
+WHERE s.a = rt.a;
+DROP FUNCTION f_ret_record();
+
+-- UPDATE ... FROM unnest() with a complex element type; area(box)
+-- yields the value to match.  The locking machinery for the
+-- non-relation RTE generates a whole-row Var that deparseColumnRef
+-- emits as ROW(f<rti>.c1, ...).
+UPDATE remote_tbl r SET b = 999
+FROM unnest(array[box '((2,3),(-2,-3))']) AS t(bx)
+WHERE r.a = area(t.bx);
+SELECT * FROM remote_tbl WHERE a IN (23, 24, 25) ORDER BY a;
+
+-- The same shape with CASE and RETURNING; exercises the DirectModify
+-- path and the executor's tuple-desc reconstruction.
+UPDATE remote_tbl r
+   SET b = CASE WHEN random() >= 0 THEN 5 ELSE 0 END
+  FROM unnest(array[box '((2,3),(-2,-3))']) AS t(bx)
+ WHERE r.a = area(t.bx) RETURNING a, b;
+
+-- RETURNING a whole-row reference to the function RTE.  Without the
+-- per-RTE function metadata being preserved on the DirectModify path
+-- (FdwDirectModifyPrivateFunctions / FdwDirectModifyPrivateMinRTIndex),
+-- this would fail with "input of anonymous composite types is not
+-- implemented".
+UPDATE remote_tbl r SET b = 7
+  FROM unnest(array[box '((2,3),(-2,-3))'],
+              array[int '1']) AS t(bx, i)
+ WHERE r.a = area(t.bx) RETURNING a, b, t;
+
+-- ROWS FROM (...) with several functions.  Force pushdown because the
+-- cost model otherwise picks a local plan.
+SET enable_hashjoin = off;
+SET enable_mergejoin = off;
+SET enable_nestloop = off;
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT r.a, t.n, t.s
+  FROM remote_tbl r, ROWS FROM (unnest(array[3, 6, 9]),
+                                generate_series(11, 13)) AS t(n, s)
+ WHERE r.a = t.n ORDER BY r.a;
+SELECT r.a, t.n, t.s
+  FROM remote_tbl r, ROWS FROM (unnest(array[3, 6, 9]),
+                                generate_series(11, 13)) AS t(n, s)
+ WHERE r.a = t.n ORDER BY r.a;
+
+-- Whole-row Var on the absorbed function side (e.g. via a cast to
+-- text).  Exercises both deparseColumnRef whole-row branch and the
+-- get_tupdesc_for_join_scan_tuples() RTE_FUNCTION metadata path.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t::text, r.a
+  FROM remote_tbl r, ROWS FROM (unnest(array[3, 6, 9]),
+                                generate_series(11, 13)) AS t(n, s)
+ WHERE r.a = t.n ORDER BY r.a;
+SELECT t::text, r.a
+  FROM remote_tbl r, ROWS FROM (unnest(array[3, 6, 9]),
+                                generate_series(11, 13)) AS t(n, s)
+ WHERE r.a = t.n ORDER BY r.a;
+
+-- Check whole-row Var represented by function on the nullable
+-- left join side
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT u, ft5.c1, ft5.c2, ft4.c1, ft4.c2 FROM ft5 LEFT JOIN
+(ft4 JOIN unnest(array[1,2], array[3,4]) as u (u1, u2) ON ft4.c1=u1)
+ON ft5.c1 = ft4.c1 WHERE ft5.c1 < 10 ORDER BY ft5.c1;
+SELECT u, ft5.c1, ft5.c2, ft4.c1, ft4.c2 FROM ft5 LEFT JOIN
+(ft4 JOIN unnest(array[1,2], array[3,4]) as u (u1, u2) ON ft4.c1=u1)
+ON ft5.c1 = ft4.c1 WHERE ft5.c1 < 10 ORDER BY ft5.c1;
+
+-- Same nullable-side whole-row Var, but with outer rows that both match
+-- and miss the (foreign x function) inner join.  A multi-column function
+-- RTE is used so that the reference is a genuine whole-row Var (a single
+-- scalar-returning function would collapse to its lone column).  This
+-- exercises the THEN ROW(...) side of deparseColumnRef()'s whole-row CASE
+-- (matched rows reconstruct the composite) as well as the NULL side
+-- (missed rows), confirming the executor rebuilds the anonymous composite
+-- correctly.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT l.a, t FROM remote_tbl l
+  LEFT JOIN (remote_tbl r JOIN unnest(array[2, 4], array[20, 40]) AS t(x, y)
+             ON r.a = t.x)
+  ON l.a = r.a
+ WHERE l.a < 6 ORDER BY l.a;
+SELECT l.a, t FROM remote_tbl l
+  LEFT JOIN (remote_tbl r JOIN unnest(array[2, 4], array[20, 40]) AS t(x, y)
+             ON r.a = t.x)
+  ON l.a = r.a
+ WHERE l.a < 6 ORDER BY l.a;
+RESET enable_hashjoin;
+RESET enable_mergejoin;
+RESET enable_nestloop;
+
+-- Check foreign join with parameterized function
+CREATE OR REPLACE FUNCTION f(int) RETURNS SETOF int LANGUAGE plpgsql ROWS 10 AS 'BEGIN RETURN QUERY SELECT generate_series(1,$1) ; END' IMMUTABLE;
+ALTER EXTENSION postgres_fdw ADD FUNCTION f(INTEGER);
+
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH s AS MATERIALIZED (SELECT r1.* FROM remote_tbl r1
+JOIN LATERAL
+(SELECT r2.a FROM remote_tbl r2, f(r1.a) LIMIT 1) s
+ON true)
+SELECT * FROM s ORDER BY 1;
+WITH s AS MATERIALIZED (SELECT r1.* FROM remote_tbl r1
+JOIN LATERAL
+(SELECT r2.a FROM remote_tbl r2, f(r1.a) LIMIT 1) s
+ON true)
+SELECT * FROM s ORDER BY 1;
+
+ALTER EXTENSION postgres_fdw DROP FUNCTION f(INTEGER);
+DROP FUNCTION f(INTEGER);
+
+-- Volatile function in ROWS FROM disqualifies the whole RTE.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT r.a FROM remote_tbl r,
+                ROWS FROM (unnest(array[3, 6, 9]),
+                           generate_series(1, 4 + (random() * 0)::int)) AS t(n, s)
+ WHERE r.a = t.n;
+
+-- LATERAL function referencing a foreign Var: postgres_fdw's
+-- foreign-join pushdown rejects this via the joinrel->lateral_relids
+-- check; the plan is therefore a local NestLoop + FunctionScan.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT r.a, t.x FROM remote_tbl r, LATERAL unnest(array[r.a]) AS t(x)
+WHERE r.a <= 3 ORDER BY r.a;
+
+-- Outer joins with the function RTE are not pushed down (only INNER
+-- joins are supported by function_rte_pushdown_ok()).
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT r.a, t.n FROM remote_tbl r
+     LEFT JOIN unnest(array[1, 2, 3]) AS t(n) ON r.a = t.n
+ WHERE r.a <= 5 ORDER BY r.a;
+
+-- SEMI join (EXISTS) with a function RTE is also not pushed down.
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT r.a FROM remote_tbl r
+ WHERE EXISTS (SELECT 1 FROM unnest(array[3, 6, 9]) AS t(n) WHERE t.n = r.a)
+ ORDER BY r.a;
+
+DROP FOREIGN TABLE remote_tbl;
+DROP TABLE base_tbl_fn;
+
 -- ====================================================================
 -- Check that userid to use when querying the remote table is correctly
 -- propagated into foreign rels present in subqueries under an UNION ALL
diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index 3fc2c2f71d0..f21ae1baeb2 100644
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -746,6 +746,30 @@ set_foreign_rel_properties(RelOptInfo *joinrel, RelOptInfo *outer_rel,
 			joinrel->fdwroutine = outer_rel->fdwroutine;
 		}
 	}
+	else if (OidIsValid(outer_rel->serverid) &&
+			 inner_rel->rtekind == RTE_FUNCTION)
+	{
+		/*
+		 * One side is a foreign relation, the other side is a function RTE.
+		 * If the function is IMMUTABLE, the FDW can absorb the function call
+		 * into the remote query (the result is identical regardless of which
+		 * server evaluates it).  Let the FDW decide whether the join is
+		 * actually shippable; here we just propagate the FDW routine so the
+		 * FDW gets a chance.
+		 */
+		joinrel->serverid = outer_rel->serverid;
+		joinrel->userid = outer_rel->userid;
+		joinrel->useridiscurrent = outer_rel->useridiscurrent;
+		joinrel->fdwroutine = outer_rel->fdwroutine;
+	}
+	else if (OidIsValid(inner_rel->serverid) &&
+			 outer_rel->rtekind == RTE_FUNCTION)
+	{
+		joinrel->serverid = inner_rel->serverid;
+		joinrel->userid = inner_rel->userid;
+		joinrel->useridiscurrent = inner_rel->useridiscurrent;
+		joinrel->fdwroutine = inner_rel->fdwroutine;
+	}
 }
 
 /*
-- 
2.43.0

Re: Function scan FDW pushdown

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