DAX essentials
Core functions and evaluation concepts. 10 cards. Click a card to flip, or use the arrow keys and space bar.
What does CALCULATE do?
Evaluates an expression in a modified filter context. It is the only function that can change filter context.
Difference between ALL and ALLSELECTED?
ALL removes all filters. ALLSELECTED removes the visual's own filter but respects slicers and page filters.
When does a measure evaluate?
At query time, inside the filter context created by the visual cell being rendered.
When does a calculated column evaluate?
At refresh, row by row, and the result is stored in the model.
What is context transition?
CALCULATE converting an existing row context into an equivalent filter context — happens inside iterators and calculated columns.
Why use DIVIDE instead of / ?
DIVIDE returns blank (or an alternate) on divide-by-zero instead of raising an error.
What does SUMX do that SUM cannot?
It iterates a table with row context, so it can evaluate a per-row expression like Qty × Price before summing.
Why does RANKX return 1 for every row?
The table argument is missing ALL, so ranking happens within each row's own context.
What does VAR do to evaluation?
Evaluates once at its definition point and captures the filter context there; it does not re-evaluate later.
KEEPFILTERS purpose?
Makes a CALCULATE filter argument intersect with the existing filter instead of replacing it.