PowerPivot, DAX and Semi-additive measures
Over the week-end I was doing some analysis on SQL Server disk usage, and wanted to be able to display current disk usage by database. Up to this point, I’d mainly been doing a SUM over my measures. Well, that would make no sense in this scenario – I’d end up with a meaningless number just like I would if I took a SUM of an Inventory value.
I found myself dealing with a classic semi-additive measure. These are easy to deal with using SQL Server Analysis Services, but a tiny bit trickier in PowerPivot.