Microsoft KB Archive/254910

= FIX: Slow Performance with NOT NULL Comparison and Empty Table =

Article ID: 254910

Article Last Modified on 3/14/2006

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APPLIES TO


 * Microsoft SQL Server 7.0 Standard Edition

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This article was previously published under Q254910



BUG #: 56596 (SQLBUG_70)



SYMPTOMS
A query that contains an aggregate function, a GROUP BY clause, and an IS NOT NULL comparison on one table and a join with an empty table may run slowly. The optimizer picks a plan that uses the table with the IS NOT NULL comparison as the outer table in the join rather than the empty table. The following is the type of query that would exhibit this problem: SELECT count(TableRows.col1), TableEmpty.col1 FROM TableRows TR, TableEmpty TE WHERE TR.col1 = TE.col1 AND TR.col2 IS NOT NULL Group By TE.col1 For the preceding query, performance is slow under the following circumstances:
 * TableRows contains sufficient data where col2 is NOT NULL such that iterating through each qualifying row has a noticeable affect on performance.
 * TableEmpty contains no data.



WORKAROUND
If the table "TableEmpty" has at least one data row, the optimizer picks the correct plan.



STATUS
Microsoft has confirmed this to be a problem in SQL Server 7.0. This problem has been corrected in U.S. Service Pack 2 for Microsoft SQL Server 7.0. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

254561 INF: How to Obtain Service Pack 2 for Microsoft SQL Server 7.0 and Microsoft Data Engine (MSDE) 1.0

For more information, contact your primary support provider.

Keywords: kbbug kbfix KB254910

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