Shawn Tayler <stay...@washoecounty.us> writes: > I run the following:
> select sfd.lid as sflid,sd.lid as slid,sfd.serial from sfd,shawns_data > sd where sfd.serial = sd.serial_number order by sfd.lid; > the lid columns in both tables should be identical, but as you see in > this sample, they do differ: > sflid | slid | serial > -------+-------+---------- > 14056 | 14056 | 9614583 > 14057 | | 9614984 > 14058 | 14058 | 9614737 > 14059 | 14059 | 9614579 > 14060 | | 9614827 > 14061 | 14061 | 9614726 > 14062 | 14062 | 9614966 > 14063 | 14063 | 9615079 > So running this query: > select count(*) from sfd,shawns_data sd where sfd.serial = sd.serial_number > and sfd.lid != sd.lid; > I should show some rows that do not match, at least 2 (there are more than > shown). > But instead I get this: > count > ------- > 0 > (1 row) Probably those "blank" values of slid are really NULLs. A NULL isn't "equal to" something else, but it isn't "unequal" either. You could use IS DISTINCT FROM instead of != in your second query. regards, tom lane -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql