Horton

Re: [BUG] Remove self joins causes 'variable not found in subplan target lists' error

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Richard Guo <guofenglinux@gmail.com>
Cc: Sergey Soloviev <sergey.soloviev@tantorlabs.ru>, Alexander Korotkov <aekorotkov@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2025-08-28T00:15:35Z
Lists: pgsql-hackers

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  1. Fix semijoin unique-ification for child relations

  2. Fix "variable not found in subplan target lists" in semijoin de-duplication.

  3. Recalculate where-needed data accurately after a join removal.

I wrote:
> This leaves us with some pretty unappetizing choices about what
> to do in v18:
> 1. Try to emulate the proposed HEAD fix.

Actually, a preliminary look suggests that we can approximate
that quite well, because v18's create_unique_path() is already
responsible for preparing the list of columns to be de-duplicated
by a UniquePath.  So we can stick the same logic about whether
make_pathkeys_for_sortclauses believes that each column adds something
into create_unique_path().  Unlike the case with HEAD, that doesn't
overlap with any useful work the function was already doing, but
I still think that the cost will be negligible in normal cases.

I'll try to have a patch along those lines by tomorrow.

			regards, tom lane