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FIX: A small number of rows are sampled in SQL Server when table statistics are updated automatically or together with specified sampling rate

Assume that you have a table that has statistics on columns that correspond to a prefix of the key of the clustered or covering non-clustered index. There are some non-covering indexes for which this condition is not true. When the statistics of the table are updated automatically or manually with a specified sampling rate, a significantly smaller number of rows are sampledfrom the sampling rate than expected. This results in non-representative statistics, and inefficient query plans may be used for the queries that use the statistics.
The issue was first fixed in the following cumulative update of SQL Server. After you apply the fix, you have to enable trace flag 4199 to make the hotfix work.

Cumulative Update 1 for SQL Server 2014

Cumulative Update 8 for SQL Server 2012 SP1

Cumulative Update 10 for SQL Server 2008 R2 SP2

About cumulative updates for SQL Server

Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. Check out the latest cumulative updates for SQL Server:
To work around the issue, manually update the statistics together with the FULLSCAN or SAMPLE option as well as with a higher sampling rate.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

Article ID: 2904010 - Last Review: 04/21/2014 19:02:00 - Revision: 3.0

Microsoft SQL Server 2008 R2 Service Pack 2, Microsoft SQL Server 2012 Service Pack 1, Microsoft SQL Server 2014 Developer, Microsoft SQL Server 2014 Enterprise, Microsoft SQL Server 2014 Standard

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