The Ultimate Guide to Power BI Aggregations

Aggregations in Power BI improve report performance by pre-summarizing data from very large fact tables, which reduces model size and query times. The guide covers both user-defined aggregations and automatic aggregations, the latter of which leverages machine learning to optimize queries. It provides a step-by-step walkthrough of creating aggregated tables, setting appropriate storage modes like DirectQuery, Import, and Dual, and establishing correct data model relationships. A critical step is using the "Manage aggregations" feature to make Power BI aware of these tables, allowing the engine to redirect queries from the slow source to the fast, in-memory aggregated cache. This process results in significant performance improvements, as demonstrated by query times dropping from seconds to milliseconds.