In Microsoft SQL Server 2008 R2, you may receive inconsistent results when you run a complex query that uses the APPLY
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
For example, the query optimizer generates a GROUP BY ColA, ColB
clause internally against the following table:
Collapse this tableExpand this table
The query optimizer may incorrectly generate an execution plan that returns both the ColA
columns. These columns are grouped by the ColA
column in the output list. In this example, the query may randomly return 0
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:
Cumulative Update package 5 for SQL Server 2008 R2
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:
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:
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:
New naming schema for Microsoft SQL Server software update packages
For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
Description of the standard terminology that is used to describe Microsoft software updates