Expression errors with "FOR UPDATE" and postgres_fdw with partition wise join enabled.

Hi,

I am getting "ERROR: unexpected expression in subquery output" and
"ERROR: variable not found in subplan target lists" errors, for "FOR
UPDATE" with postgres_fdw. (when set enable_partition_wise_join to true);

Attached patch have queries which are throwing mentioned error on running
make check in contrib/postgres_fdw folder.

An independent test case to reproduce this is given below.

SET enable_partition_wise_join TO true;

CREATE EXTENSION postgres_fdw;
CREATE SERVER fdw_server FOREIGN DATA WRAPPER postgres_fdw OPTIONS (dbname
'postgres', port '5432', use_remote_estimate 'true');
CREATE USER MAPPING FOR PUBLIC SERVER fdw_server;

CREATE TABLE pt1 ( c1 int NOT NULL, c2 int NOT NULL, c3 text)PARTITION BY
RANGE(c1);
CREATE TABLE pt1p1 (like pt1);
CREATE TABLE pt1p2 (like pt1);

CREATE TABLE pt2 (c1 int NOT NULL, c2 int NOT NULL, c3 text) PARTITION BY
RANGE(c1);
CREATE TABLE pt2p1 (like pt2);
CREATE TABLE pt2p2 (like pt2);

INSERT INTO pt1p1 SELECT id, id + 1,'AAA' || to_char(id, 'FM000') FROM
generate_series(-100, -1) id;
INSERT INTO pt1p2 SELECT id, id + 1,'AAA' || to_char(id, 'FM000') FROM
generate_series(1, 99) id;
INSERT INTO pt2p1 SELECT id, id + 1,'AAA' || to_char(id, 'FM000') FROM
generate_series(-100, -1) id;
INSERT INTO pt2p2 SELECT id, id + 1,'AAA' || to_char(id, 'FM000') FROM
generate_series(1, 99) id;

CREATE FOREIGN TABLE ft1p1 PARTITION OF pt1 FOR VALUES FROM (MINVALUE) TO
(0) SERVER fdw_server OPTIONS (table_name 'pt1p1');
CREATE FOREIGN TABLE ft1p2 PARTITION OF pt1 FOR VALUES FROM (0) TO
(MAXVALUE) SERVER fdw_server OPTIONS (table_name 'pt1p2');
CREATE FOREIGN TABLE ft2p1 PARTITION OF pt2 FOR VALUES FROM (MINVALUE) TO
(0) SERVER fdw_server OPTIONS (table_name 'pt2p1');
CREATE FOREIGN TABLE ft2p2 PARTITION OF pt2 FOR VALUES FROM (0) TO
(MAXVALUE) SERVER fdw_server OPTIONS (table_name 'pt2p2');

ANALYZE pt1;
ANALYZE pt2;
ANALYZE ft1p1;
ANALYZE ft1p2;
ANALYZE ft2p1;
ANALYZE ft2p2;

EXPLAIN (VERBOSE, COSTS OFF)
SELECT t1.c1, ss.a, ss.b FROM (SELECT c1 FROM pt1 WHERE c1 = 50) t1 INNER
JOIN (SELECT t2.c1, t3.c1 FROM (SELECT c1 FROM pt1 WHERE c1 between 50 and
60) t2 FULL JOIN (SELECT c1 FROM pt2 WHERE c1 between 50 and 60) t3 ON
(t2.c1 = t3.c1) WHERE t2.c1 IS NULL OR t2.c1 IS NOT NULL) ss(a, b) ON
(TRUE) ORDER BY t1.c1, ss.a, ss.b FOR UPDATE OF t1;
ERROR: unexpected expression in subquery output

EXPLAIN (VERBOSE, COSTS OFF)
SELECT t1.c1, ss.a, ss.b FROM (SELECT c1 FROM pt1) t1 INNER JOIN (SELECT
t2.c1, t3.c1 FROM (SELECT c1 FROM pt1) t2 FULL JOIN (SELECT c1 FROM pt1) t3
ON (t2.c1 = t3.c1)) ss(a, b) ON (TRUE) ORDER BY t1.c1, ss.a, ss.b FOR
UPDATE OF t1;
ERROR: variable not found in subplan target lists

Thanks & Regards,
Rajkumar Raghuwanshi
QMG, EnterpriseDB Corporation