Kevin Traster <kevin@xxxxxxxxxx> writes: > Regarding the previous posts about the same issues of PERFORMENCE between > NOT IN versus EXCEPT. There has not been any answer to explain it - just > talk about the differenences between the two results. > > Yes, I can still get the results using EXCEPT but it would be nice to no why > I can't get NOT IN to complete the simple query. There are two answers here. One you've already been given, that NOT IN has to handle NULLs specially and that makes these plans not equivalent. The NOT IN is decidedly harder to solve. The other answer is that EXCEPT is a set operation which in Postgres uses a completely different set of logic. Even if you used NOT EXISTS which really is equivalent to EXCEPT the resulting plans would be different. Which one would be better would depend on the circumstances. In an ideal world every equivalent query would generate identical plans. We don't live in an ideal world and Postgres isn't perfect. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com Ask me about EnterpriseDB's Slony Replication support! -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
