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From: Tender Wang <tndrwang@gmail.com>
Date: Fri, 10 Apr 2026 20:49:24 +0800
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 <CAHewXN=_C3apEh4nDndgbOiYnFAYDDuMWAozPP0G3iL=7zQbJg@mail.gmail.com>
Subject: Re: pg17: XX000: no relation entry for relid 0
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: pgsql-hackers@lists.postgresql.org,
	Paul Jungwirth <pj@illuminatedcomputing.com>, Tom Lane <tgl@sss.pgh.pa.us>
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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
>
> Since 9391f7152.
The varno =3D 0 is from below code:

*pTargetList =3D generate_setop_tlist(colTypes, colCollations,
                                                0,
                                                false,
                                                *pTargetList,
                                                refnames_tlist,
                                                &trivial_tlist);
            *istrivial_tlist =3D trivial_tlist;
            target =3D create_pathtarget(root, *pTargetList);

in recurse_set_operations().
When calling set_pathtarget_cost_width(), we estimate the length of
the array that would enter estimate_array_length().
Before 9391f7152, we returned 10 directly.  But now, we see if we can
find any statistics about it.
In examine_variable(), try to find base_rel in find_base_rel(), error
reported. Because the varno of the Var is 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/selfu=
ncs.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 *arraye=
xpr)
                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?

--=20
Thanks,
Tender Wang