2010/11/10 Bjørn T Johansen <btj@xxxxxxxxxx>: > select * from table where field is null > > And when I run explain, it tells me that it uses seq scan... Is this because pg thinks that seq scan is as fast as using indexes or because using index on "is null" queries does > not work? > Does the table have *lots* of NULLs in that column? If the index is not very selective, it may choose to use a seq scan since it will result in fewer I/O ops. This decision will be based on the relative values of random_page_cost and seq_page_cost, and probably the effective_cache_size as well. -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
