On 20/11/2023 15:49, Richard Guo wrote:
> I'm wondering if we can relax this restriction because it seems to me
> that a PHV evaluated/needed at or below the self join should not have
> problem if we remove the self join.
>
>
> After some more thought, I think PHVs should not impose any constraints
> on removing self joins. If the removed rel is contained in the relids
> that a PHV is evaluated/needed at or laterally references, it can just
> be replaced with the rel that is kept.
>
> Attached is a patch to remove such constraints. Any comments or
> feedback are welcome.
Carrying out excavations, I found that it was Teodor Sigaev who added
this limitation in v.20 of the patch in an earlier stage of the development.
I also had analyzed this part of code and came to the conclusion that it
doesn't needed. Only a paranoid approach and the absence of an
alternative opinion are the reasons why this code is still exists.
Your patch is ok.
I think the comment, 'PHVs should not impose ...' looks redundant. It
may be enough to have it in the commit comment.
--
regards,
Andrei Lepikhov
Postgres Professional
