DAX (Data Analysis Expressions) Mastery

Overview

Complete DAX reference covering evaluation contexts, CALCULATE, time intelligence, iterators, table functions, performance optimization, and advanced patterns. DAX is the formula language for Power BI measures, calculated columns, calculated tables, and RLS filters.

Evaluation Contexts

Row Context

• Created by: Calculated columns, iterators (SUMX, FILTER, AVERAGEX, etc.), row-by-row evaluation
• Each row in the table has its own row context
• Access columns directly: Sales[Amount]
• Nested iterators create nested row contexts

Filter Context

• Created by: Slicers, visual filters, page filters, report filters, CALCULATE arguments
• Determines which rows are visible to aggregation functions
• Does NOT provide row-level access (cannot use Sales[Amount] directly in a measure without aggregation)