Re: pg17: XX000: no relation entry for relid 0

On Fri, Apr 10, 2026 at 9:49 PM Tender Wang <tndrwang(at)gmail(dot)com> wrote:
> Justin Pryzby <pryzby(at)telsasoft(dot)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

> 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.

- Richard