FIX: A Distinct Count measure may return incorrect values if you define aggregations on the non-overlapping partitions in a distinct count measure group in SSAS 2008 R2

Consider the following scenario:

• You install Microsoft SQL Server 2008 R2 Analysis Services (SSAS 2008 R2).
• You create non-overlapping partitions in a measure group. The measure group contains a measure that uses the DistinctCount function.
  
  Note Non-overlapping partitions are partitions that have non-overlapping value ranges.
• You define aggregations on the non-overlapping partitions.
• You run a multidimensional expression (MDX) query that queries the DistinctCount measure.

In this scenario, the DistinctCount measure may return incorrect values. For example, the returned value may be double or triple the actual value.

This issue occurs because the usage of an aggregation in the MDX query causes SSAS 2008 R2 to incorrectly scan the aggregation multiple times. This issue only occurs when you set up non-overlapping partitions that contain the DistinctCount measure.

Cumulative update information

SQL Server 2008 R2

The fix for this issue was first released in Cumulative Update 6. 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: 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:

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.