On Thu, 18 Apr 2002 Maarten.Boekhold@reuters.com wrote:
>
> On 04/17/2002 01:44:46 PM Michael Loftis wrote:
> > In many of the cases where it is a primary key it is also there to
> > ensure fast lookups when referenced as a foreign key. Or for joins.
>
> 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
restrictsthe 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 ...
Cheers
Tycho
--
Tycho Fruru tycho.fruru@conostix.com
"Prediction is extremely difficult. Especially about the future." - Niels Bohr
