| From: | Peter Eisentraut <peter(at)eisentraut(dot)org> |
|---|---|
| To: | David Rowley <dgrowleyml(at)gmail(dot)com>, Zhang Mingli <zmlpostgres(at)gmail(dot)com> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Remove useless GROUP BY columns considering unique index |
| Date: | 2024-09-18 07:28:30 |
| Message-ID: | bdd253fc-22c6-4d29-8f0e-79bf47961e67@eisentraut.org |
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| Lists: | pgsql-hackers |
On 12.09.24 03:43, David Rowley wrote:
> On Sat, 30 Dec 2023 at 04:05, Zhang Mingli <zmlpostgres(at)gmail(dot)com> wrote:
>> So my patch make it easy: check unique index’s columns, it’s a valid candidate if all of that have NOT NULL constraint.
>> And we choose a best one who has the least column numbers in get_min_unique_not_null_attnos(), as the reason: less columns mean that more group by columns could be removed.
>
> This patch no longer applies. We no longer catalogue NOT NULL
> constraints, which this patch is coded to rely upon.
Work is ongoing to revive the patch that catalogs not-null constraints:
<https://commitfest.postgresql.org/49/5224/>. This patch should
probably wait for that patch at the moment.
> (Likely it could just look at pg_attribute.attnotnull instead)
That won't work because you can't record dependencies on that. (This is
one of the reasons for cataloging not-null constraints as real constraints.)
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