Re: Remove useless GROUP BY columns considering unique index
От | Zhang Mingli |
---|---|
Тема | Re: Remove useless GROUP BY columns considering unique index |
Дата | |
Msg-id | 1f16fc31-0946-4b9d-8d21-f7d23155872c@Spark обсуждение исходный текст |
Ответ на | Re: Remove useless GROUP BY columns considering unique index (David Rowley <dgrowleyml@gmail.com>) |
Список | pgsql-hackers |
Hi, all
I haven't paid attention to this topic in a long time, thanks all for the advices, I will study them then update.
Thanks again.
www.hashdata.xyz
On Sep 18, 2024 at 15:50 +0800, David Rowley <dgrowleyml@gmail.com>, wrote:
On Wed, 18 Sept 2024 at 19:28, Peter Eisentraut <peter@eisentraut.org> wrote:
On 12.09.24 03:43, David Rowley wrote:(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.)
I'm not seeing any need to record constraint dependencies for this
optimisation. It would be different for detecting functional
dependencies in a view using a unique constraint+not null constraints
for ungrouped columns, but that's not what this is. This is just a
planner optimisation. The plan can be invalidated by a relcache
invalidation, which will happen if someone does ALTER TABLE DROP NOT
NULL.
For reference, see 5b736e9cf.
David
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