> Would return the row. Now with an upgrade to PostgreSQL 7.3 (yes, I know > there are many changes and we're working through them right now) the same > query returns nothing. Dropping the "AND parent_id = NULL" returns the row > as expected.
NULL is similar to UNKNOWN. So, NULL = NULL is the similar to UNKNOWN = UNKNOWN. Since you don't know it, how can you tell if they're equal or not? Syntax you're looking for is: AND parent_id IS NULL If you really really really need = NULL (due to some MS product which ignores SQL standards -- say MS Access) there is a toggle in the postgresql.conf file to allow automated conversion of = NULL to IS NULL within the server.
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