Microsoft distributes Microsoft SQL Server 2008 R2 fixes as one downloadable file. Because the fixes are cumulative, each new release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2008 R2 fix release.
In Microsoft SQL Server 2008 R2, you may receive inconsistent results when you run a complex query that uses the APPLY operator.
Note You receive the correct result in this scenario if you use the FORCE ORDER query hint in a query.
This issue occurs because the query optimizer selects an incorrect execution plan for the query.
The query optimizer handles the GROUP BY predicate for the multiple columns in a physical operator of the execution plan. However, the operator outputs all the grouped columns in the output list and does not group all these columns. Therefore, the query may return an incorrect result.
Note An example of a physical operator is the Stream Aggregate operator.
For example, the query optimizer generates a GROUP BY ColA, ColB clause internally against the following table:
The query optimizer may incorrectly generate an execution plan that returns both the ColA and ColB columns. These columns are grouped by the ColA column in the output list. In this example, the query may randomly return 0 or 1 in the ColB column if the values in the ColA column are 0.
Cumulative update information
SQL Server 2008 R2
The fix for this issue was first released in Cumulative Update 5. For more information about how to obtain this cumulative update package for SQL Server 2008 R2, click the following article number to view the article in the Microsoft Knowledge Base:
2438347 Cumulative Update package 5 for SQL Server 2008 R2 Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2008 R2 fix release. We recommend that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
981356 The SQL Server 2008 R2 builds that were released after SQL Server 2008 R2 was released
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
To verify that you are experiencing this issue, review the execution plan of the problematic query, and then check the group operators. For example, check the stream aggregate operator, the hash aggregate operator, the distinct sort operator, and the segment operator. If the list of the output columns is longer than the list of the grouped columns, you are experiencing this issue.
For more information about the Incremental Servicing Model for SQL Server, click the following article number to view the article in the Microsoft Knowledge Base:
935897 An Incremental Servicing Model is available from the SQL Server team to deliver hotfixes for reported problems
For more information about the naming schema for SQL Server updates, click the following article number to view the article in the Microsoft Knowledge Base:
822499New naming schema for Microsoft SQL Server software update packagesFor more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates