Stephane Bortzmeyer <bortzmeyer@xxxxxx> writes: > Yes, PostgreSQL is right and implement the standard. Now, what's the > rationale for the standard? I understand it for a single column but, > for several columns, it should be still possible to have different > tuples, such as (3, NULL) and (5, NULL) for instance. If that's what you want, declare it as UNIQUE not PRIMARY KEY. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://archives.postgresql.org