| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Richard Guo <guofenglinux(at)gmail(dot)com> |
| Cc: | Sergey Soloviev <sergey(dot)soloviev(at)tantorlabs(dot)ru>, Alexander Korotkov <aekorotkov(at)gmail(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Subject: | Re: [BUG] Remove self joins causes 'variable not found in subplan target lists' error |
| Date: | 2025-08-28 00:15:35 |
| Message-ID: | 1484250.1756340135@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
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
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