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>
Subject: Re: UNION removes almost all rows (not duplicates) - in fresh build
 of pg17!
In-reply-to: <Zktzf926vslR35Fv@depesz.com>
References: <Zktzf926vslR35Fv@depesz.com>
Comments: In-reply-to hubert depesz lubaczewski <depesz@depesz.com>
	message dated "Mon, 20 May 2024 17:59:59 +0200"
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Date: Mon, 20 May 2024 13:11:24 -0400
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hubert depesz lubaczewski <depesz@depesz.com> writes:
> $ select count(*) from ( select * from pg_class where relkind =3D 'r' un=
ion select * from pg_class where relkind =3D 'i' );
>  count
> =E2=94=80=E2=94=80=E2=94=80=E2=94=80=E2=94=80=E2=94=80=E2=94=80
>      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