Re: [SQL] SubQuery speed

andreas(dot)fredriksson(at)pacer(dot)se wrote:
>
> BEGIN;
> DECLARE CURSOR curs FOR
> SELECT url,title FROM idx_files WHERE id IN (
> SELECT file_id FROM idx_ref WHERE word_id IN (
> SELECT id FROM idx_words WHERE word = 'search term 1' OR .. ) );
> FETCH FORWARD 10 IN curs;
> END;
>
> The idx_files table holds about 1.000 rows, the idx_words table holds
> about 50.000 words, and the idx_ref is a massive 250.000+
> row cross-reference (file_id, word_id) which links the words and
> pages together.
>
> A query like the above took several hours on my Pentium 200 at work before
> I killed the stuck daemon. This is kind of strange since the innermost
> subquery is only suppose to return a single id. :-(
>
> Are there any alternate methods of solving this? I don't think it's
> possible to write this kind of query using a multi-JOIN?

Try to rewrite query using EXISTS instead of IN and create
indices.

Vadim