Hash join

Can any one explain me this "Option [hash join]"...
what that Option [hash join] will effect in this query.
select * from [group] inner join patientgroup on PA_PatientID = PG_PatientID
Option [hash join]
Thanks
Noor
Noor wrote:
> Can any one explain me this "Option [hash join]"...
> what that Option [hash join] will effect in this query.
> select * from [group] inner join patientgroup on PA_PatientID =
> PG_PatientID Option [hash join]
>
> Thanks
> Noor
It will force SQL Server to use a hash join on the tables instead of a
nested loop join or a merge join. Generally, you want to let SQL Server
make up its own mind about what the best join operation is. Essentially,
a hash join forces SQL Server to create hash values on both tables in
order to determine the matching values.
To see how it affects your query test it in Query Analyzer with and
without the hint.
See Understanding Hash Joins in the BOL.
David G.