FIX: SQL Server Optimizer May Underestimate the Cardinality of Range Queries

View products that this article applies to.

BUG #: 364245 (SQL Server 8.0)

SYMPTOMS

The SQL Server optimizer may not correctly estimate the cardinality of an expression if all the following conditions are true:

The query specifies two different range conditions, such as column BETWEEN x and y or column > x.
Both of the range predicates are qualified with an AND condition.
A histogram is available for each of the two columns, either from manual or auto create statistics or from an index that specifies the column as its leading column.
Multicolumn density is available for the combination of the two columns.

The following query is an example of a query that may be affected by this problem:

SELECT *
FROM    a  
WHERE	 a.[SALESORG] BETWEEN 'B001' AND 'B099'  AND     
	 a.[SOLD_TO] BETWEEN 'B000000001' AND 'B000010000'

In this example, histograms must exist for both SALESORG and SOLD_TO, and statistics must exist for the combination of SALESORG and SOLD_TO.

Because of this bug, the SQL Server optimizer typically underestimates the number of rows from such a predicate. The SQL Server optimizer may select a plan that is not efficient, such as using an index seek when an index scan is more appropriate, using an incorrect join order, or failing to use a matching indexed view.

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RESOLUTION

Service pack information

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

290211 (http://support.microsoft.com/kb/290211/ ) How to obtain the latest SQL Server 2000 service pack

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Hotfix information

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

Date         Time   Version            Size    File name
--------------------------------------------------------------
27-Mar-2003  02:47  2.4.1.0        11,172,351  Sql2000-kb810185-8.00.0794-enu.exe

Note Because of file dependencies, the most recent hotfix or feature that contains these files may also contain additional files.

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STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.This problem was first corrected in Microsoft SQL Server 2000 Service Pack 4.

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