Adam Rich wrote: > -- Query A > select count(*) from customers c > where not exists ( select 1 from orders o > where o.customer_id = c.customer_id ) > > -- Query B > select count(*) from customers c > where customer_id not in ( select customer_id from orders) > > -- Query C > select count(*) from customers c > left join orders o on c.customer_id = o.customer_id > where o.order_id is null > > I believe they all achieve the same thing.
I think not. When using INSERT INTO customers VALUES (1); INSERT INTO customers VALUES (2); INSERT INTO customers VALUES (NULL); and INSERT INTO orders VALUES (1); INSERT INTO orders VALUES (3); INSERT INTO orders VALUES (NULL); I get Query A: 2 Query B: 0 Query C: 3 -- Peter Eisentraut http://developer.postgresql.org/~petere/ ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org/
