> Hello,
>
> I am hoping someone can help explain why modifying the following
> query can effect such a huge change in speed. The query is:
>
> select * from articles
> where exists
> ( select 1 from article_categories
> where
> article_categories.article_id = articles.id and
> article_categories.category_id is null
> )
>
Can you test these two queries?select * from (select article_id from article_categories where category_id is null
groupby article_id) X join articles using (article_id);
select <fields> from article_categories join articles using (article_id) where category_id is null group by
<fields>
Above queries will need index on article_idI'm not sure if it helps, but they are the only solutions in mymind ;-)
Can you say anything about data statistics in your tables? Howmany rows are with category_id=null?
I looked into query definition once again. Your query doesn't makesense - article_categories have not null
category_id...What do you reallywant to do?
Regards,
Tomasz Myrta
