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From: Tender Wang <tndrwang@gmail.com>
Date: Sat, 11 Apr 2026 09:31:59 +0800
Message-ID: 
 <CAHewXNkBL9rh1SqVArtchK3mwq3BXyTk7sArZgQJBnqhQZ=TCw@mail.gmail.com>
Subject: Re: pg17: XX000: no relation entry for relid 0
To: Richard Guo <guofenglinux@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>, pgsql-hackers@lists.postgresql.org,
	Paul Jungwirth <pj@illuminatedcomputing.com>, Tom Lane <tgl@sss.pgh.pa.us>,
	Michael Paquier <michael@paquier.xyz>
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Richard Guo <guofenglinux@gmail.com> =E4=BA=8E2026=E5=B9=B44=E6=9C=8810=E6=
=97=A5=E5=91=A8=E4=BA=94 22:39=E5=86=99=E9=81=93=EF=BC=9A
>
> On Fri, Apr 10, 2026 at 9:49=E2=80=AFPM Tender Wang <tndrwang@gmail.com> =
wrote:
> > Justin Pryzby <pryzby@telsasoft.com> =E4=BA=8E2026=E5=B9=B44=E6=9C=8810=
=E6=97=A5=E5=91=A8=E4=BA=94 18:54=E5=86=99=E9=81=93=EF=BC=9A
> > > CREATE VIEW x AS SELECT NULL::int[]
> > > UNION ALL SELECT NULL::int[]
> > > UNION ALL SELECT ARRAY[NULL::bigint];
> > >
> > > SELECT FROM x;
> > > ERROR:  XX000: no relation entry for relid 0
>
> Nice catch.  It seems that we need at least three branches to
> reproduce this, so that there's a nested UNION ALL whose output type
> doesn't match the parent's expected type.  At the outer branch maybe
> we can use NULL::bigint[] instead to be a little simpler.
>
> SELECT NULL::int[] UNION ALL SELECT NULL::int[] UNION ALL SELECT NULL::bi=
gint[];
> ERROR:  no relation entry for relid 0

Yes, add it to the test case.

>
> > I didn't think too much at now, a quick fix as below:
> > diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/s=
elfuncs.c
> > index 4160d2d6e24..ff93fc3ac8a 100644
> > --- a/src/backend/utils/adt/selfuncs.c
> > +++ b/src/backend/utils/adt/selfuncs.c
> > @@ -2265,6 +2265,9 @@ estimate_array_length(PlannerInfo *root, Node *ar=
rayexpr)
> >                 AttStatsSlot sslot;
> >                 double          nelem =3D 0;
> >
> > +               if (IsA(arrayexpr, Var) && ((Var *) arrayexpr)->varno =
=3D=3D 0)
> > +                       return 10;
> > +
> >                 examine_variable(root, arrayexpr, 0, &vardata);
> >                 if (HeapTupleIsValid(vardata.statsTuple))
> >                 {
> >
> > Any thoughts?
>
> This looks like the right fix to me.  We can use some comment here.

comments added.
Please see the attached patch.

--=20
Thanks,
Tender Wang

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