On Fri, 06 Aug 2004 13:17:42 -0400, Michael Stassen
<[EMAIL PROTECTED]> wrote:
> You need a LEFT JOIN:
>
> SELECT ticket_number
> FROM purchased_items LEFT JOIN purchases
> ON purchased_items.ticket_number = purchases.ticket_number
> WHERE purchases.ticket_number IS NULL;
No, actually he doesn't.
SELECT ticket_number
FROM purchased_items
WHERE ticket_number NOT IN
(SELECT ticket_number FROM purchases);
The above will most certainly be faster than any join, because it is
only a couple projections and a simple selection over ticket_number
(which is almost certainly indexed).
Although, I suppose if this is only a maintenance query (I suspect it
is), then it probably doesn't matter. But, the bottom line is: if you
can avoid join, do it. There's only so much the query optimizer can
do.
--
Matt Warden
Berry Neuroscience Lab
Department of Psychology
Miami University
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