On 04/18/2002 12:41:15 PM tycho wrote:
> > Don't know if the optimizer takes this into consideration, but a query that 
> uses a primary and/or unique key in the where-clause, should always choose to 
> use
> > the related indices (assuming the table size is above a certain threshold). 
> Since a primary key/unique index always restricts the resultset to a single 
> row.....
> 
> I don't think so.
> 
> eg. table with primary key "pk", taking values from 1 to 1000000 (so
> 1000000 records)
> 
> select * from table where pk > 5
> 
> should probably not use the index ...

Oops, you're right of course. Rephrase the above as 'a query that uses a primary key to uniquely qualify a single row' (which pretty much restricts it to the = operator with a constant). Still, this is probably a fairly common case.....

Maarten

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Fri, 19 Apr 2002 13:27:05 +0400
Maarten.Boekhold@reuters.com
Re: Index Scans become Seq Scans after VACUUM ANALYSE