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
>
>
