On Sun, 4 Oct 2026 at 14:00, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> and the reason it doesn't fail is that the AppendPath has nil pathkeys
> in this case. So (I speculate that) we never attached pathkeys to a
> UNION ALL AppendPath before, and the reason we're trying to now has
> something to do with having reduced the child list to a singleton.
It looks like a bug in add_setop_child_rel_equivalences(). It wrongly
assumes that setop_pathkeys will contain a PathKey for each tlist
entry. The problem query has a redundant PathKey due to the WHERE a =
1.
I think the fix needs to be either don't remove redundant pathkeys for
setop_pathkeys or use some other method to figure out which
expressions to add in add_child_eq_member().
David
