On Mon, 19 Nov 2001, Arsalan Zaidi wrote:
> Hi.
>
> The following query takes absolutely *ages* to run. Even with just a 1000
> records in each table. It seems to me that the nested query is being run for
> *every* value in the dom_ns table.
>
> SELECT DISTINCT dom_ns.domname, dom_ns.tldtype FROM dom_ns WHERE
> dom_ns.domname NOT IN (SELECT domname FROM domains WHERE domname IS NOT
> NULL);
>
> Why should is this happening? I just want the nested query to run once!
See the FAQ. Short form: It'll be faster if you rewrite to use exists
rather than IN.