Re: Slow Queries with OR's?

On Fri, May 02, 2003 at 09:54:19AM +0100, Mr Mat psql-mail wrote:
> Tom - Thanks for your help - it's invaluable!
>
> I have now gone back to my original query shown below:
> I set EXPLAIN ANALYZE running on it over 12 hours ago and its still
> going! (Yesterdays EXPLAIN ANALYZE took tens of minutes)
> So I have included just the ouput from EXPLAIN.
>
>
> SELECT msg_id, from_line, col_date FROM news_messages WHERE msg_id IN(
> SELECT msg_id FROM news_msg_id_ng_id_link WHERE ng_id IN(
> SELECT ng_id FROM news_ng_genre_link WHERE genre_id in (3,6)
> )
> )

Question: How is that query different from:

SELECT a.msg_id, a.from_line, a.col_date
FROM news_messages a, news_msg_id_ng_id_link b, news_ng_genre_link c
WHERE c.genre_id in (3,6)
AND b.ng_id = c.ng_id
AND a.msg_id = b.msg_id;

(Maybe I'm missing something with NULLs ?)
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> "the West won the world not by the superiority of its ideas or values or
> religion but rather by its superiority in applying organized violence.
> Westerners often forget this fact, non-Westerners never do."
> - Samuel P. Huntington