Bob,
There's some discussion of it at
http://dev.mysql.com/doc/refman/5.0/en/rewriting-subqueries.html.
PB
-----
Bob Gailer wrote:
> 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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