FIX: Combination of Multiple EXIST, OR, and Subquery Clauses May Give a Sub-Optimal Plan (294874)


The information in this article applies to:

  • Microsoft SQL Server 2000 (all editions)
This article was previously published under Q294874
BUG #: 352700 (SHILOH_BUGS)

SYMPTOMS

You may see performance degradation when both of the following conditions are met:
  • OR is used on multiple EXISTS subqueries in the WHERE clause.

  • The subqueries also have EXISTS.

CAUSE

Under a very narrow set of circumstances that involve multiple OR, EXIST, and subquery clauses, the estimated I/O for the various steps may be incorrectly combined, which results in a sub-optimal plan choice.

RESOLUTION

To resolve this problem, obtain the latest service pack for SQL Server 2000. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

290211 INF: How to Obtain the Latest SQL Server 2000 Service Pack

WORKAROUND

Rewrite the query to use joins rather than subqueries.

STATUS

Microsoft has confirmed that this is a problem in SQL Server 2000. This problem was first corrected in SQL Server 2000 Service Pack 1.
Modification Type:MajorLast Reviewed:11/6/2003
Keywords:kbBug kbfix kbSQLServ2000sp1fix KB294874
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