Introducing DAX


In this chapter, you learned many new functions and started looking at some DAX code. You may not remember all the functions right away, but the more you use them, the more familiar they will become.

The more crucial topics you learned in this chapter are

  • Calculated columns are columns in a table that are computed with a DAX expression. Calculated columns are computed at data refresh time and do not change their value depending on user selection.

  • Measures are calculations expressed in DAX. Instead of being computed at refresh time like calculated columns are, measures are computed at query time. Consequently, the value of a measure depends on the user selection in the report.

  • Errors might happen at any time in a DAX expression; it is preferable to detect the error condition beforehand rather than letting the error happen and intercepting it after the fact.

  • Aggregators like SUM are useful to aggregate columns, whereas to aggregate expressions, you need to use iterators. Iterators work by scanning a table and evaluating an expression row by row. At the end of the iteration, iterators aggregate a result according to their semantics.

In the next chapter, you will continue on your learning path by studying the most important table functions available in DAX.