im puzzled

Hi , this is my query SELECT users.uid FROM users, picks WHERE users.uid = picks.user_id; this works correctly. The results are what they are supposed to be: However, when I change the = sign to a <> or !=, The results are completely incorrect. ---------------------------------- picks.user_id contains: 5, 1, 7, 8, 9, 12, 13, 15 users.uid contains: 1, 8, 9, 5, 7, 10, 11, 12, 13, 14, 15 the result for SELECT users.uid FROM users, picks WHERE users.uid = picks.user_id; is: 5, 1, 7, 8, 9, 12, 13, 15 and the result for SELECT users.uid FROM users, picks WHERE users.uid <> picks.user_id; is: 1, 7, 8, 9, 10, 11, 12, 13, 14, 15, 5, 7, 8, 9, 10, 11,12, 13, 14, 15, 1, 5, 8, 9, 10 ,11...etc it goes on for 80 rows with no particular pattern......H.E.L.P.!.