"Jozsef Szalay" <jszalay@storediq.com> writes:
> Execute the following query:
> SELECT *
> FROM (SELECT id, 0 AS value
> FROM test
> WHERE description = 'abc'
> ) t1
> FULL OUTER JOIN
> (SELECT id, 1 AS value
> FROM test
> WHERE description = 'def'
> ) t2 USING (id, value);
Hm. It's reducing the join condition to constant FALSE (since 0<>1) and
then deciding it doesn't know how to join in that case. While this is
certainly undesirable, I have to wonder about the purpose of the query.
It seems like this is just a remarkably inefficient way of performing
UNION ALL. Do you have a more real-world case where it happens?
regards, tom lane
