Re: BUG #19742: `INTERSECT` under a `UNION ALL` with an empty arm fails with "could not find pathkey item t"

PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
> Please see the repro. Seems like a regression; 19beta4 and the current main
> branch both have this error raised, but 18.6 works fine. I ran it with psql

> CREATE TABLE d (a int);
> INSERT INTO d VALUES (1), (1), (2), (NULL), (3);
> SELECT * FROM (SELECT a FROM d INTERSECT ALL SELECT a FROM d
> UNION ALL SELECT a FROM d WHERE false) s
> WHERE a = 1;
> -- ERROR: XX000: could not find pathkey item to sort

Bisecting shows this started with

fdda78e361f136ec2b8de579b366c1e66bba1199 is the first bad commit
commit fdda78e361f136ec2b8de579b366c1e66bba1199
Author: David Rowley <drowley(at)postgresql(dot)org>
Date: Wed Nov 5 11:48:09 2025 +1300

Fix possible usage of incorrect UPPERREL_SETOP RelOptInfo

03d40e4b5 allowed dummy UNION [ALL] children to be removed from the plan
by checking for is_dummy_rel(). That commit neglected to still account
for the relids from the dummy rel so that the correct UPPERREL_SETOP
RelOptInfo could be found and used for adding the Paths to.

I suspect that that commit just allowed reaching some pre-existing
mistake, but I've not dug into it.

regards, tom lane