Re: Re-Reason of Slowness of Query - Mailing list pgsql-performance

From tv@fuzzy.cz
Subject Re: Re-Reason of Slowness of Query
Date
Msg-id c054efdf315e1df9376b2646077ef805.squirrel@sq.gransy.com
Whole thread Raw
In response to Re: Re-Reason of Slowness of Query  (Adarsh Sharma <adarsh.sharma@orkash.com>)
Responses Re: Re-Reason of Slowness of Query  (Chetan Suttraway <chetan.suttraway@enterprisedb.com>)
List pgsql-performance
> I just want to retrieve that id 's from page_content which do not have
> any entry in clause2 table.

In that case the query probably does not work (at least the query you've
sent in the first post) as it will return even those IDs that have at
least one other row in 'clause2' (not matching the != condition). At least
that's how I understand it.

So instead of this

select distinct(p.crawled_page_id)
from page_content p, clause2 c where p.crawled_page_id != c.source_id ;

you should probably do this

select distinct(p.crawled_page_id)
from page_content p left join clause2 c on (p.crawled_page_id =
c.source_id) where (c.source_id is null);

I guess this will be much more efficient too.

regards
Tomas


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