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From: =?UTF-8?Q?Fran=C3=A7ois_Jehl?= <francois.jehl@pigment.com>
Date: Tue, 21 Apr 2026 09:40:47 +0200
Message-ID: <CABZtAYZwSQfMgvQXKPiQ5v23UWms_y4hwxXtbxbUWYjwsou5Lw@mail.gmail.com>
Subject: Re: BUG #19460: FULL JOIN rewriting issue on empty queries
To: Richard Guo <guofenglinux@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-bugs@lists.postgresql.org, 
	Robert Haas <robertmhaas@gmail.com>
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Thanks Tom and Richard for the quick diagnosis and fix, I should be the one
saying thanks here!

Fran=C3=A7ois

On Tue, Apr 21, 2026 at 1:04=E2=80=AFAM Richard Guo <guofenglinux@gmail.com=
> wrote:

> On Tue, Apr 21, 2026 at 7:40=E2=80=AFAM Tom Lane <tgl@sss.pgh.pa.us> wrot=
e:
> > Ah: equivclass.c doesn't mind letting em->em_relids be an alias
> > for the left_relids or right_relids of some source RestrictInfo.
> > That's not problematic as long as those are all constants after
> > construction of the EquivalenceClass, but when remove_rel_from_eclass
> > is trying to change things, it's a big problem.
>
> ha, I just came to the same conclusion.
>
> > This seems to do the trick to fix it, although I'm going to wait
> > for a valgrind regression run to finish before deciding this
> > is enough:
>
> This seems safe enough to me.  LGTM.
>
> - Richard
>

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<div dir=3D"ltr">Thanks Tom and Richard for the quick diagnosis and fix, I =
should be the one saying thanks here!<div><br></div><div>Fran=C3=A7ois</div=
></div><br><div class=3D"gmail_quote gmail_quote_container"><div dir=3D"ltr=
" class=3D"gmail_attr">On Tue, Apr 21, 2026 at 1:04=E2=80=AFAM Richard Guo =
&lt;<a href=3D"mailto:guofenglinux@gmail.com">guofenglinux@gmail.com</a>&gt=
; wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px=
 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">On Tue,=
 Apr 21, 2026 at 7:40=E2=80=AFAM Tom Lane &lt;<a href=3D"mailto:tgl@sss.pgh=
.pa.us" target=3D"_blank">tgl@sss.pgh.pa.us</a>&gt; wrote:<br>
&gt; Ah: equivclass.c doesn&#39;t mind letting em-&gt;em_relids be an alias=
<br>
&gt; for the left_relids or right_relids of some source RestrictInfo.<br>
&gt; That&#39;s not problematic as long as those are all constants after<br=
>
&gt; construction of the EquivalenceClass, but when remove_rel_from_eclass<=
br>
&gt; is trying to change things, it&#39;s a big problem.<br>
<br>
ha, I just came to the same conclusion.<br>
<br>
&gt; This seems to do the trick to fix it, although I&#39;m going to wait<b=
r>
&gt; for a valgrind regression run to finish before deciding this<br>
&gt; is enough:<br>
<br>
This seems safe enough to me.=C2=A0 LGTM.<br>
<br>
- Richard<br>
</blockquote></div>

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