The problem is that the special optimization that was proposed for the case
where the subquery has no WHERE clause isn't valid when the subquery returns
no rows. That additional optimization needs to be removed, and preferably
replaced with some sort of efficient run-time test.
-----
Jim Finnerty, AWS, Amazon Aurora PostgreSQL
--
Sent from: http://www.postgresql-archive.org/PostgreSQL-hackers-f1928748.html
