nested select query take too long

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!

Thanks in advance.

--Arsalan.

-------------------------------------------------------------------
People often hate those things which they do not know, or cannot understand.
--Ali Ibn Abi Talib (AS)