In response to Robert Edwards : > A. Kretschmer wrote: > >In response to Robert Edwards : > >>Can anyone suggest a way that I can impose uniqueness on a and b when > >>c is NULL? > > > >Sure, use a functional index: > > > >test=# create table bobtest (a int, b int, c int); > >CREATE TABLE > >test=*# create unique index idx_bobtest on > >bobtest(a,b,coalesce(c::text,'NULL')); > >CREATE INDEX > >test=*# insert into bobtest (a, b) values (1, 4); > >INSERT 0 1 > >test=*# insert into bobtest (a, b, c) values (1, 4, NULL); > >ERROR: duplicate key value violates unique constraint "idx_bobtest" > >test=!# > > > > > >Regards, Andreas > > Beautiful!
Btw: if your data doesn't contains 0 or negative, you can use coalesce(c,0) or coalesce(c,-1). It would be better for searching. Andreas -- Andreas Kretschmer Kontakt: Heynitz: 035242/47150, D1: 0160/7141639 (mehr: -> Header) GnuPG-ID: 0x3FFF606C, privat 0x7F4584DA http://wwwkeys.de.pgp.net -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql
