Right.... So, how are these different: SELECT * FROM t1 WHERE id EXISTS (SELECT id FROM t2)
If there are *any* results for the subselect, the exists returns true. It's the equivalent of: select * from t1 where id is true; ie select * from t1; If there are no results for the subselect, the exists returns false, ie: select * from t1 where false; which will return nothing.
to SELECT * FROM t1 WHERE id IN (SELECT id FROM t2)
this returns specific id's that match.
According to my understanding of the documentation, these would have the same result.
No, they aren't. create table t1(id int, name varchar(5)); insert into t1(id, name) values (1, 'one'); insert into t1(id, name) values (2, 'two'); insert into t1(id, name) values (3, 'three'); insert into t1(id, name) values (4, 'four'); insert into t1(id, name) values (5, 'five'); create table t2(id int, other_name varchar(5)); insert into t2(id, other_name) values (1, 'one'); insert into t2(id, other_name) values (2, 'two'); this returns everything from t1: SELECT * FROM t1 WHERE EXISTS (SELECT id FROM t2); this returns 2 rows that match: SELECT * FROM t1 WHERE id IN (SELECT id FROM t2); -- Postgresql & php tutorials http://www.designmagick.com/ -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
