From: Andrey Lepikhov <a.lepikhov@postgrespro.ru>
To: PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>
Subject: Clause accidentally pushed down ( Possible bug in Making Vars outer-join aware)
Date: Wed, 22 Feb 2023 12:48:45 +0600
Message-ID: <0b819232-4b50-f245-1c7d-c8c61bf41827@postgrespro.ru> (raw)
Hi,
sqlancer benchmark raised an issue with pushing down clauses in LEFT
JOINs. Example:
DROP TABLE IF EXISTS t1,t2,t3,t4 CASCADE;
CREATE TABLE t1 AS SELECT true AS x FROM generate_series(0,1) x;
CREATE TABLE t2 AS SELECT true AS x FROM generate_series(0,1) x;
CREATE TABLE t3 AS SELECT true AS x FROM generate_series(0,1) x;
CREATE TABLE t4 AS SELECT true AS x FROM generate_series(0,1) x;
ANALYZE;
EXPLAIN (ANALYZE, COSTS OFF)
SELECT ALL t1.x FROM t1, t2
LEFT OUTER JOIN t3
ON t3.x
LEFT OUTER JOIN t4
ON t3.x
WHERE t4.x ISNULL;
We should get zero tuples, right? But we have the explain:
Nested Loop (actual time=0.024..0.028 rows=4 loops=1)
...
REL_15_STABLE works correctly. As I remember, it could be induces by new
machinery, introduced by the 'Making Vars outer-join aware' patch.
Sorry for flood, if you are working on that issue.
--
regards,
Andrey Lepikhov
Postgres Professional
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To: pgsql-bugs@postgresql.org
Cc: a.lepikhov@postgrespro.ru, pgsql-bugs@lists.postgresql.org
Subject: Re: Clause accidentally pushed down ( Possible bug in Making Vars outer-join aware)
In-Reply-To: <0b819232-4b50-f245-1c7d-c8c61bf41827@postgrespro.ru>
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