Horton

Re: Removing unneeded self joins

Alexander Lakhin <exclusion@gmail.com>

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From: Alexander Lakhin <exclusion@gmail.com>
To: Andrei Lepikhov <a.lepikhov@postgrespro.ru>, Alexander Korotkov <aekorotkov@gmail.com>
Cc: "Gregory Stark (as CFM)" <stark.cfm@gmail.com>, Michał Kłeczek <michal@kleczek.org>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Richard Guo <guofenglinux@gmail.com>
Date: 2024-01-08T20:00:01Z
Lists: pgsql-hackers

Commits

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  1. Remove GUC_NOT_IN_SAMPLE from enable_self_join_elimination

  2. Put enable_self_join_elimination into postgresql.conf.sample

  3. Get rid of ojrelid local variable in remove_rel_from_query()

  4. Implement Self-Join Elimination

  5. Revert: Remove useless self-joins

  6. Replace lateral references to removed rels in subqueries

  7. Replace relids in lateral subquery parse tree during SJE

  8. Forbid SJE with result relation

  9. Fix misuse of RelOptInfo.unique_for_rels cache by SJE

  10. Replace the relid in some missing fields during SJE

  11. Revert 56-bit relfilenode change and follow-up commits.

  12. Stabilize timetz test across DST transitions.

  13. Speed up finding EquivalenceClasses for a given set of rels

  14. Fix mark-and-restore-skipping test case to not be a self-join.

Hello Andrei and Alexander,

Please look at the following query which produces an incorrect result since
d3d55ce57:
CREATE TABLE t(a int PRIMARY KEY, b int);
INSERT INTO t VALUES  (1, 1), (2, 1);
SELECT * FROM t WHERE EXISTS (SELECT * FROM t t2 WHERE t2.a = t.b AND t2.b > 0);

  a | b
---+---
  1 | 1
(1 row)

I think that the expected result is:
  a | b
---+---
  1 | 1
  2 | 1
(2 rows)

Best regards,
Alexander