Jay Levitt <jay.levitt@xxxxxxxxx> writes: > When I run the following query: > select questions.id > from questions > join ( > select u.id as user_id > from users as u > left join scores as s > on s.user_id = u.id > ) as subquery > on subquery.user_id = questions.user_id; > the subquery is scanning my entire user table, even though it's restricted > by the outer query. (My real subquery is much more complicated, of course, > but this is the minimal fail case.) > Is this just not a thing the optimizer can do? Every release since 8.2 has been able to reorder joins in a query written that way. Probably it just thinks it's cheaper than the alternatives. (Unless you've reduced the collapse_limit variables for some reason?) regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
