Re: Teaching planner to short-circuit empty UNION/EXCEPT/INTERSECT inputs

I finally decided that it was a bit too obscure a scenario to test to
verify that the same silly mistake didn't reappear.

Thanks again for the report and the simple recreation steps.

Thank you for the fix!

But while playing around, I've just discovered another interesting error:

SET enable_seqscan = 'off';
SELECT * FROM t EXCEPT SELECT * FROM t
UNION SELECT * FROM pt;

leads to:
ERROR:  XX000: no relation entry for relid 0
LOCATION:  find_base_rel, relnode.c:541

Best regards,
Alexander