Re: Removing unneeded self joins - Mailing list pgsql-hackers

From Alexander Korotkov
Subject Re: Removing unneeded self joins
Date
Msg-id CAPpHfdtGBX+oATYRoMyxcyQeuKCeYT3J3kDs_MA9AwberJrUfA@mail.gmail.com
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In response to Re: Removing unneeded self joins  (Alena Rybakina <a.rybakina@postgrespro.ru>)
Responses Re: Removing unneeded self joins
List pgsql-hackers
Hi, Alena!

On Sun, Apr 6, 2025 at 12:02 AM Alena Rybakina
<a.rybakina@postgrespro.ru> wrote:
> Should we add more regression tests covering these cases?
>
> I experimented with some examples like this and noticed that it does affect cardinality estimation, though I'm not
surethe impact is significant. 
> I used the tables from the regression tests, so if they’re appropriate for reproducing this case, it should be
straightforwardto add them. 

Thank you for your feedback.  I've check the cases you've provided.  I
found that the differences here are related to the SJE itself, not to
changes regarding PHVs handling.  I think it generally OK that
estimates are somewhat changed due to such significant query
transformation.  Hopefully they should be improved in the majority of
cases.

I did some improvements to PHVs patch: revised comments and commit
message.  I'm going to push it if no objections.

------
Regards,
Alexander Korotkov
Supabase

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