Re: UNION removes almost all rows (not duplicates) - in fresh build of pg17!

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

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

To: depesz@depesz.com

Cc: pgsql-bugs mailing list <pgsql-bugs@postgresql.org>, David Rowley <dgrowleyml@gmail.com>

Date: 2024-05-20T17:11:24Z

Lists: pgsql-bugs

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Fix generate_union_paths for non-sortable types.
- c37267162e88 17.0 landed
Doc: remove 66c0185a3 from release notes.
- e1e83a71715f 17.0 landed
Revert commit 66c0185a3 and follow-on patches.
- 7204f35919b7 17.0 landed
doc PG 17 relnotes: adjust vacuum items
- d2a04470aa64 17.0 cited
Allow planner to use Merge Append to efficiently implement UNION
- 66c0185a3d14 17.0 cited

hubert depesz lubaczewski <depesz@depesz.com> writes:
> $ select count(*) from ( select * from pg_class where relkind = 'r' union select * from pg_class where relkind = 'i' );
>  count
> ───────
>      1
> (1 row)

Ugh, that is awful.  Bisecting shows it broke at

commit 66c0185a3d14bbbf51d0fc9d267093ffec735231
Author: David Rowley <drowley@postgresql.org>
Date:   Mon Mar 25 14:31:14 2024 +1300

    Allow planner to use Merge Append to efficiently implement UNION

I've not looked at the patch, but somehow it's totally forgetting
what it's supposed to be unique-ifying on.

			regards, tom lane