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postgres_fdw: Avoid pulling up restrict infos from subqueries

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

Reported-by: Robins Tharakan <tharakan@gmail.com>
Bug: #18852
Discussion: https://postgr.es/m/CAEP4nAzryLd3gwcUpFBAG9MWyDfMRX8ZjuyY2XXjyC_C6k%2B_Zw%40mail.gmail.com
Author: Alexander Pyhalov <a.pyhalov@postgrespro.ru>
Reviewed-by: Alexander Korotkov <aekorotkov@gmail.com>
Backpatch-through: 17
This commit is contained in:
Alexander Korotkov 2025-03-25 05:49:47 +02:00
parent adb5f85fa5
commit 023fb51275
3 changed files with 79 additions and 8 deletions
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38
contrib/postgres_fdw/expected/postgres_fdw.out
View File

@ -4936,6 +4936,44 @@ SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
----+----+----+----+----+----+----+----+----+----+----
(0 rows)
-- Semi-join conditions shouldn't pop up as left/right join clauses.
SET enable_material TO off;
EXPLAIN (verbose, costs off)
SELECT x1.c1 FROM
(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x1
RIGHT JOIN
(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x2
ON (x1.c1 = x2.c1)
ORDER BY x1.c1 LIMIT 10;
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Foreign Scan
Output: ft2.c1
Relations: ((public.ft2 ft2_1) LEFT JOIN ((public.ft2) SEMI JOIN (public.ft4))) SEMI JOIN (public.ft4 ft4_1)
Remote SQL: SELECT s9.c1 FROM ("S 1"."T 1" r6 LEFT JOIN (SELECT r4."C 1" FROM "S 1"."T 1" r4 WHERE ((r4.c2 < 10)) AND EXISTS (SELECT NULL FROM "S 1"."T 3" r5 WHERE ((r4."C 1" = r5.c1)))) s9(c1) ON (((s9.c1 = r6."C 1")))) WHERE ((r6.c2 < 10)) AND EXISTS (SELECT NULL FROM "S 1"."T 3" r7 WHERE ((r6."C 1" = r7.c1))) ORDER BY s9.c1 ASC NULLS LAST LIMIT 10::bigint
(4 rows)
SELECT x1.c1 FROM
(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x1
RIGHT JOIN
(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x2
ON (x1.c1 = x2.c1)
ORDER BY x1.c1 LIMIT 10;
c1
----
2
4
6
8
10
12
14
16
18
20
(10 rows)
RESET enable_material;
-- Can't push down semi-join with inner rel vars in targetlist
EXPLAIN (verbose, costs off)
SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE

16
contrib/postgres_fdw/postgres_fdw.c
View File

@ -5963,15 +5963,31 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
break;
case JOIN_LEFT:
/*
* When semi-join is involved in the inner or outer part of the
* left join, it's deparsed as a subquery, and we can't refer to
* its vars on the upper level.
*/
if (bms_is_empty(fpinfo_i->hidden_subquery_rels))
fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
fpinfo_i->remote_conds);
if (bms_is_empty(fpinfo_o->hidden_subquery_rels))
fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
fpinfo_o->remote_conds);
break;
case JOIN_RIGHT:
/*
* When semi-join is involved in the inner or outer part of the
* right join, it's deparsed as a subquery, and we can't refer to
* its vars on the upper level.
*/
if (bms_is_empty(fpinfo_o->hidden_subquery_rels))
fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
fpinfo_o->remote_conds);
if (bms_is_empty(fpinfo_i->hidden_subquery_rels))
fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
fpinfo_i->remote_conds);
break;

17
contrib/postgres_fdw/sql/postgres_fdw.sql
View File

@ -1455,6 +1455,23 @@ SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
WHERE ft2.c1 > 900
ORDER BY ft2.c1 LIMIT 10;
-- Semi-join conditions shouldn't pop up as left/right join clauses.
SET enable_material TO off;
EXPLAIN (verbose, costs off)
SELECT x1.c1 FROM
(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x1
RIGHT JOIN
(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x2
ON (x1.c1 = x2.c1)
ORDER BY x1.c1 LIMIT 10;
SELECT x1.c1 FROM
(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x1
RIGHT JOIN
(SELECT * FROM ft2 WHERE EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft2.c1 AND ft2.c2 < 10)) x2
ON (x1.c1 = x2.c1)
ORDER BY x1.c1 LIMIT 10;
RESET enable_material;
-- Can't push down semi-join with inner rel vars in targetlist
EXPLAIN (verbose, costs off)
SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE