UPDATE: PowerPivot for Excel 2010 in SQL Server 2012 and Excel 2013 support the DISTINCTCOUNT aggregation in DAX. This blog post is relevant only if you use PowerPivot for Excel 2010 in SQL Server 2008 R2. A PivotTable based on PowerPivot data doesn’t  Read more

UPDATE: This blog post is still good for learning DAX principles, but a better description of many-to-many patterns is available on The Many-to-Many Revolution whitepaper that is available here: http://www.sqlbi.com/articles/many2many/ – please download  Read more