Article ID: 244230
Article Last Modified on 3/14/2006
APPLIES TO
- Microsoft SQL Server 7.0 Standard Edition
This article was previously published under Q244230
BUG #: 55001 (SQLBUG_70)
SYMPTOMS
A query that contains a correlated subquery with an OR EXISTS clause may perform slowly.
WORKAROUND
You can rewrite the query and include a redundant clause in the subquery as shown in the following code example:
select A.col1 from TableA A, TableB B
where
A.col1 = B.col1
and B.col2 = 'X'
and
(A.col2 = 'Y'
or exists (select * from tableC C
where A.col3 = C.col3
-- Add redundant clause from outer query
and B.col2 = 'X'
)
)
STATUS
Microsoft has confirmed this to be a problem in SQL Server 7.0. This problem has been corrected in U.S. Service Pack 1 for Microsoft SQL Server 7.0. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
232570INF: How to Obtain Service Pack 1 for Microsoft SQL Server 7.0 and Microsoft Data Engine (MSDE) 1.0
For more information, contact your primary support provider.
MORE INFORMATION
The following sample code demonstrates the problem:
select A.col1 from TableA A, TableB B
where
A.col1 = B.col1
and B.col2 = 'X'
and
(A.col2 = 'Y'
or exists (select * from tableC C
where A.col3 = C.col3
--and B.col2 = 'X'
)
)
The SHOWPLAN output for this query shows the optimizer is picking a hash match join strategy.
Keywords: kbbug kbfix kbqfe KB244230
