FIX: Error message when you estimate the compression on a table in SQL Server 2008: "Subquery returned more than 1 value"

When you use the sp_estimate_data_compression_savings stored procedure on a table that has both a nonclustered primary key and one or more nonclustered indexes in Microsoft SQL Server 2008, you may receive the following error message: Although you receive this error message, the result is returned. However, the compression estimations for some nonclustered indexes are incorrect.

This problem occurs whether or not a clustered index exists.

Service pack information

To resolve this problem, obtain the latest service pack for SQL Server 2008. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

Cumulative update information

The fix for this issue was first released in Cumulative Update 2. For more information about how to obtain this cumulative update package for SQL Server 2008, click the following article number to view the article in the Microsoft Knowledge Base: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 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:

To work around this problem, specify the @index_id parameter when you run the sp_estimate_data_compression_savings stored procedure. You must run the stored procedure one time for each index for which you want to estimate.

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 SQL Server 2008 Service Pack 1.

The sp_estimate_data_compression_savings stored procedure is used to return the current size of tables. The sp_estimate_data_compression_savings stored procedure also estimates the table size for the requested compression state.

Steps to reproduce the problem

1. Start SQL Server Management Studio, and then connect to an instance of SQL Server 2008.
2. Create a new query, and then run the following statements.

   CREATE DATABASE TEST
   GO
   USE Test
   GO
   
   CREATE TABLE REPRO(i int primary key nonclustered, a int)
   GO
   
   CREATE NONCLUSTERED INDEX NONCLUSTERED_REPRO ON REPRO(a)
   GO
   
   EXEC SP_ESTIMATE_DATA_COMPRESSION_SAVINGS @schema_name = 'dbo', @object_name = 'repro', @index_id = NULL, @partition_number = NULL, @data_compression = 'PAGE'
   

For more information about what files are changed, and for information about any prerequisites to apply the cumulative update package that contains the hotfix that is described in this Microsoft Knowledge Base article, click the following article number to view the article in the Microsoft Knowledge Base:

For more information about the list of builds that are available after the release of SQL Server 2008, click the following article number to view the article in the Microsoft Knowledge Base: 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: 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: For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base: