Re: Re-Reason of Slowness of Query

On Wed, Mar 23, 2011 at 4:08 PM, <tv(at)fuzzy(dot)cz> wrote:

> > 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.
>
> true.

> 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.
>
>
This looks like to give expected results. Also note that the where clause
"is null" is really required and is not an
optional predicate.

> regards
> Tomas
>
>
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--
Regards,
Chetan Suttraway
EnterpriseDB <http://www.enterprisedb.com/>, The Enterprise
PostgreSQL<http://www.enterprisedb.com/>
company.