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Add support for deparsing semi-joins to contrib/postgres_fdw

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

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

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

Author: Alexander Pyhalov
Reviewed-by: Ashutosh Bapat, Ian Lawrence Barwick, Yuuki Fujii, Tomas Vondra
Discussion: https://postgr.es/m/c9e2a757cf3ac2333714eaf83a9cc184@postgrespro.ru
This commit is contained in:
Alexander Korotkov
2023-12-05 22:53:12 +02:00
parent 278eb13c48
commit 824dbea3e4
5 changed files with 699 additions and 83 deletions
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126
contrib/postgres_fdw/sql/postgres_fdw.sql
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@ -600,7 +600,7 @@ WITH t (c1_1, c1_3, c2_1) AS MATERIALIZED (SELECT t1.c1, t1.c3, t2.c1 FROM ft1 t
-- ctid with whole-row reference
EXPLAIN (VERBOSE, COSTS OFF)
SELECT t1.ctid, t1, t2, t1.c1 FROM ft1 t1 JOIN ft2 t2 ON (t1.c1 = t2.c1) ORDER BY t1.c3, t1.c1 OFFSET 100 LIMIT 10;
-- SEMI JOIN, not pushed down
-- SEMI JOIN
EXPLAIN (VERBOSE, COSTS OFF)
SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
SELECT t1.c1 FROM ft1 t1 WHERE EXISTS (SELECT 1 FROM ft2 t2 WHERE t1.c1 = t2.c1) ORDER BY t1.c1 OFFSET 100 LIMIT 10;
@ -1305,6 +1305,130 @@ explain (verbose, costs off) select * from ft3 where f2 = 'foo' COLLATE "C";
explain (verbose, costs off) select * from ft3 f, loct3 l
where f.f3 = l.f3 COLLATE "POSIX" and l.f1 = 'foo';
-- ===================================================================
-- test SEMI-JOIN pushdown
-- ===================================================================
EXPLAIN (verbose, costs off)
SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
WHERE ft2.c1 > 900
AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
ORDER BY ft2.c1;
SELECT ft2.*, ft4.* FROM ft2 INNER JOIN ft4 ON ft2.c2 = ft4.c1
WHERE ft2.c1 > 900
AND EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)
ORDER BY ft2.c1;
-- The same query, different join order
EXPLAIN (verbose, costs off)
SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
(SELECT * FROM ft4 WHERE
EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
ON ft2.c2 = ft4.c1
WHERE ft2.c1 > 900
ORDER BY ft2.c1;
SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
(SELECT * FROM ft4 WHERE
EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
ON ft2.c2 = ft4.c1
WHERE ft2.c1 > 900
ORDER BY ft2.c1;
-- Left join
EXPLAIN (verbose, costs off)
SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
(SELECT * FROM ft4 WHERE
EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
ON ft2.c2 = ft4.c1
WHERE ft2.c1 > 900
ORDER BY ft2.c1 LIMIT 10;
SELECT ft2.*, ft4.* FROM ft2 LEFT JOIN
(SELECT * FROM ft4 WHERE
EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
ON ft2.c2 = ft4.c1
WHERE ft2.c1 > 900
ORDER BY ft2.c1 LIMIT 10;
-- Several semi-joins per upper level join
EXPLAIN (verbose, costs off)
SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
(SELECT * FROM ft4 WHERE
EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
ON ft2.c2 = ft4.c1
INNER JOIN (SELECT * FROM ft5 WHERE
EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
ON ft2.c2 <= ft5.c1
WHERE ft2.c1 > 900
ORDER BY ft2.c1 LIMIT 10;
SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
(SELECT * FROM ft4 WHERE
EXISTS (SELECT 1 FROM ft5 WHERE ft4.c1 = ft5.c1)) ft4
ON ft2.c2 = ft4.c1
INNER JOIN (SELECT * FROM ft5 WHERE
EXISTS (SELECT 1 FROM ft4 WHERE ft4.c1 = ft5.c1)) ft5
ON ft2.c2 <= ft5.c1
WHERE ft2.c1 > 900
ORDER BY ft2.c1 LIMIT 10;
-- Semi-join below Semi-join
EXPLAIN (verbose, costs off)
SELECT ft2.* FROM ft2 WHERE
c1 = ANY (
SELECT c1 FROM ft2 WHERE
EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
AND ft2.c1 > 900
ORDER BY ft2.c1 LIMIT 10;
SELECT ft2.* FROM ft2 WHERE
c1 = ANY (
SELECT c1 FROM ft2 WHERE
EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2))
AND ft2.c1 > 900
ORDER BY ft2.c1 LIMIT 10;
-- Upper level relations shouldn't refer EXISTS() subqueries
EXPLAIN (verbose, costs off)
SELECT * FROM ft2 ftupper WHERE
EXISTS (
SELECT c1 FROM ft2 WHERE
EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
AND ftupper.c1 > 900
ORDER BY ftupper.c1 LIMIT 10;
SELECT * FROM ft2 ftupper WHERE
EXISTS (
SELECT c1 FROM ft2 WHERE
EXISTS (SELECT 1 FROM ft4 WHERE ft4.c2 = ft2.c2) AND c1 = ftupper.c1 )
AND ftupper.c1 > 900
ORDER BY ftupper.c1 LIMIT 10;
-- EXISTS should be propogated to the highest upper inner join
EXPLAIN (verbose, costs off)
SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
(SELECT * FROM ft4 WHERE EXISTS (
SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
ON ft2.c2 = ft4.c1
INNER JOIN
(SELECT * FROM ft2 WHERE EXISTS (
SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
ON ft2.c2 = ft21.c2
WHERE ft2.c1 > 900
ORDER BY ft2.c1 LIMIT 10;
SELECT ft2.*, ft4.* FROM ft2 INNER JOIN
(SELECT * FROM ft4 WHERE EXISTS (
SELECT 1 FROM ft2 WHERE ft2.c2 = ft4.c2)) ft4
ON ft2.c2 = ft4.c1
INNER JOIN
(SELECT * FROM ft2 WHERE EXISTS (
SELECT 1 FROM ft4 WHERE ft2.c2 = ft4.c2)) ft21
ON ft2.c2 = ft21.c2
WHERE ft2.c1 > 900
ORDER BY ft2.c1 LIMIT 10;
-- Can't push down semi-join with inner rel vars in targetlist
EXPLAIN (verbose, costs off)
SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
ft1.c1 IN (
SELECT ft2.c1 FROM ft2 JOIN ft4 ON ft2.c1 = ft4.c1)
ORDER BY ft1.c1 LIMIT 5;
-- ===================================================================
-- test writable foreign table stuff
-- ===================================================================