Re: Why would this slow the query down so much?

On Monday 15 October 2001 16:12 pm, Tom Lane wrote:
> Stuart Grimshaw <nospam@smgsystems.co.uk> writes:
> > SELECT a.category, b.headline, b.added, c.friendlyname
> > FROM caturljoin as a
> >         INNER JOIN stories as b ON (a.url = b.source)
> >         INNER JOIN urllist as c ON (a.url = d.urn)
> > WHERE a.category = 93 ORDER BY b.added DESC LIMIT 1;
>
> (I assume "d.urn" is a typo for "c.urn"...)
>
> The query plan you show looks pretty reasonable if the planner's row
> count estimates are in the right ballpark.  How many caturljoin rows
> have category = 93?  How many stories rows will match each caturljoin
> row?  How many urllist rows ditto?

There are 194 rows in caturljoin where url = 93, 29806 rows in stories will 
match those 194 rows and only 1 row in urllist will match.

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