Re: Removing unneeded self joins

Alexander Korotkov <aekorotkov@gmail.com>

From: Alexander Korotkov <aekorotkov@gmail.com>

To: Alexander Lakhin <exclusion@gmail.com>

Cc: Andrei Lepikhov <a.lepikhov@postgrespro.ru>, "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: 2024-01-08T22:09:49Z

Lists: pgsql-hackers

Commits

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Remove GUC_NOT_IN_SAMPLE from enable_self_join_elimination
- 717d0e8dd945 18.0 landed
Put enable_self_join_elimination into postgresql.conf.sample
- c2d329260cd8 18.0 landed
Get rid of ojrelid local variable in remove_rel_from_query()
- e167191dc146 18.0 landed
Implement Self-Join Elimination
- fc069a3a6319 18.0 cited
Revert: Remove useless self-joins
- d1d286d83c0e 17.0 landed
Replace lateral references to removed rels in subqueries
- 466979ef031a 17.0 landed
Replace relids in lateral subquery parse tree during SJE
- 489072ab7a9e 17.0 landed
Forbid SJE with result relation
- 8c441c082797 17.0 landed
Fix misuse of RelOptInfo.unique_for_rels cache by SJE
- 30b4955a4668 17.0 landed
Replace the relid in some missing fields during SJE
- a7928a57b9f0 17.0 landed
Revert 56-bit relfilenode change and follow-up commits.
- a448e49bcbe4 16.0 cited
Stabilize timetz test across DST transitions.
- 4a071afbd056 14.0 cited
Speed up finding EquivalenceClasses for a given set of rels
- 3373c7155350 13.0 cited
Fix mark-and-restore-skipping test case to not be a self-join.
- 24d08f3c0a1f 12.0 landed

On Mon, Jan 8, 2024 at 10:20 PM Alexander Korotkov <aekorotkov@gmail.com> wrote:
> On Mon, Jan 8, 2024 at 10:00 PM Alexander Lakhin <exclusion@gmail.com> wrote:
> > 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)
>
> Thank you for your report.  I'm looking at this now.

Fixed in 30b4955a46.

------
Regards,
Alexander Korotkov