When creating calculated columns or measures in Analysis Services Tabular Mode, we use DAX expression language for adding them. DAX offers number of functions for implementing them and almost all general functions such as SUM, COUNT, AVERAGE are exist too. However some functions behave differently when compare these function behavior with other tools. Here is an example;
Assume that you need to get a count of two columns related to a loaded data table. Let's say we have loaded Internet Sales table from AdventureWorksDW2014, and need to create Count of Promotion Key and Count of Sales Order Number (of course, there is no business logic on these two counts, it is only for demo purposes), then we add two measures like below;
Once added, you will see that CountPromotionKey works fine but CountSalesOrderNumber does not work. The reason for this is, Count function in DAX only works with numeric and dates. For counting non-numeric values, COUNTA has to use instead of COUNT.
Note that both functions do not count blank values. If you want to get the count including blank values, use COUNTROWS function. In addition to these, COUNTX and COUNTAX are given too. They are for getting the count based on a filter.
For getting the count only on blank values, use COUNTBLANK.