Nested grouping using GROUPBY vs SUMMARIZE
DAX introduced a GROUPBY function that should replace SUMMARIZE in some scenarios. This article describes how to use GROUPBY in nested grouping scenarios and other improvements.
Limitations of SUMMARIZE
The SUMMARIZE function in DAX is a powerful one, but – at the same time – it is also hard to use. It can be used to perform grouping and joins between tables, as we previously described in the Grouping Data article. Unfortunately, it has some well-known performance issues when computing aggregated values. It is worth to remember that you should always follow the patterns described in Best Practices Using SUMMARIZE and ADDCOLUMNS. We also wrote a more detailed analysis of internal behaviors in All the secrets of SUMMARIZE.
Tags: dax