"Dirschel, Steve" <steve.dirschel@xxxxxxxxxxxxxxxxxx> writes: > Is Postgres able to drive the query the same way with the NOT IN as the > NOT EXISTS is doing or is that only available if the query has a NOT > EXISTS? NOT IN is not optimized very well in PG, because of the strange semantics that the SQL spec demands when the sub-query produces any null values. There's been some interest in detecting cases where we can prove that the subquery produces no nulls and then optimizing it into NOT EXISTS, but it seems like a lot of work for not-great return, so nothing's happened (yet). Perhaps Oracle does something like that already, or perhaps they're just ignoring the semantics problem; they do not have a reputation for hewing closely to the spec on behavior regarding nulls. regards, tom lane
