Re: pg17: XX000: no relation entry for relid 0 - Mailing list pgsql-hackers

Richard Guo <guofenglinux@gmail.com> 于2026年4月10日周五 22:39写道：
>
> On Fri, Apr 10, 2026 at 9:49 PM Tender Wang <tndrwang@gmail.com> wrote:
> > Justin Pryzby <pryzby@telsasoft.com> 于2026年4月10日周五 18:54写道：
> > > 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::bigint[];
> 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/selfuncs.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 *arrayexpr)
> >                 AttStatsSlot sslot;
> >                 double          nelem = 0;
> >
> > +               if (IsA(arrayexpr, Var) && ((Var *) arrayexpr)->varno == 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.

--
Thanks,
Tender Wang