David Newall wrote:
PostgreSQL version: 7.4.3 (RPMs from ftp.au.postgresql.org)
Operating Sysem: Fedora Core 1
CREATE TABLE t(i integer UNIQUE); INSERT INTO t VALUES (null); INSERT INTO t VALUES (null); SELECT coalesce(i,-999) FROM t; coalesce ---------- -999 -999 (2 rows)
As someone says NULL = NULL is false so that two rows are different. If you want enforce only one null value for that column you have to write you own trigger.
Regards Gaetano Mendola
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