From: | Andrei Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru> |
---|---|
To: | Richard Guo <guofenglinux(at)gmail(dot)com>, Alexander Korotkov <aekorotkov(at)gmail(dot)com> |
Cc: | zuming(dot)jiang(at)inf(dot)ethz(dot)ch, pgsql-bugs(at)lists(dot)postgresql(dot)org, PG Bug reporting form <noreply(at)postgresql(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Subject: | Re: BUG #18187: Unexpected error: "variable not found in subplan target lists" triggered by JOIN |
Date: | 2023-11-22 02:32:06 |
Message-ID: | e6cecb71-1b3c-4fba-826a-f176bc3639be@postgrespro.ru |
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Lists: | pgsql-bugs |
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
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