Michael Stassen wrote:
Bob Gailer wrote:
Peter Brawley wrote:
Grant,
>If I want to select all the products that are in the product_table,
>but not in the sale_table, how to make the query? The
product_table >has all the products, but the sale table is a subset
of the product_table.
SELECT * FROM product_table p
LEFT JOIN sale_table s USING (prod_id)
WHERE s.prod_id IS NULL;
I have not tested that but I don't think it will work. Try:
Why not? This is the classic LEFT JOIN solution. It will work in all
versions of mysql.
Oops. I'm red-faced. Good humbling for my first appearance on this list.
It can only get better? This is a good lesson in SQL for me. I did not
know that a where clause could apply to rows in the result.
I haver searched in vain to find a clear definition of WHERE that
explains this behavior. Any pointers?
SELECT item_name FROM product_table WHERE prod_id not in (select
prod_id from sale_table);
This will work only in mysql 4.1+, and will almost certainly be
slower, because mysql's optimizer tends to treat the subquery as
dependent, meaning it will be rerun for each and every row of the
product_table.
Michael
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