On Wed, Feb 14, 2007 at 10:01:58AM +0100, Steven Lambert wrote: > You are right, the index has more columns and one of them have most of the > time the value NULL. > It is the date when the record has been "deleted"
See "Unique Constraints" in the documentation, in particular the last paragraph: http://www.postgresql.org/docs/8.1/interactive/ddl-constraints.html#AEN2016 "However, null values are not considered equal in this comparison. That means even in the presence of a unique constraint it is possible to store duplicate rows that contain a null value in at least one of the constrained columns." This has been discussed before; search the archives for words like "null", "unique", and "comparison" or "compare". -- Michael Fuhr ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org
