A DAX measure is evaluated in filter context. A slicer, visual row and relationship can change which rows contribute to a measure. CALCULATE evaluates an expression with a modified filter context.

These Power BI interview questions use a fictional two-region model. The arithmetic is intentionally small so you can predict the result before opening a report.

What fixture makes the context visible?

Region: one unique row per RegionId
RegionId | Name
N        | North
S        | South

Sales: one row per transaction
SaleId | RegionId | Amount
1      | N        | 40
2      | N        | 60
3      | S        | 50

Create an active one-to-many relationship from Region to Sales, with Region filtering Sales. There are no date or product filters in this first exercise. The unfiltered sales amount is 150.

How can two measures differ?

Sales Amount = SUM(Sales[Amount])

Sales All Regions =
    CALCULATE([Sales Amount], REMOVEFILTERS(Region))

Region Share = DIVIDE([Sales Amount], [Sales All Regions])

With North selected through Region, Sales Amount is 100. Sales All Regions is 150 because the Region filters are removed. Region Share is two-thirds. South gives 50, 150 and one-third respectively.

Create these as separate measures. The display format can show the share as a percentage. The measure's numeric value and its visual formatting are different things.

Does “all regions” remove every filter?

No. This expression removes filters from Region. It does not mean ignore all dates, products or every fact-table filter. Add another dimension later and verify which filters remain.

If a visual filters Sales[RegionId] directly rather than Region, removing Region filters is not the same operation as removing that fact-column filter. Specify the actual field used by the report. A vague “the region filter” can hide the source of a wrong denominator.

What is row context?

Row context identifies a current row, such as during an iterator or calculated-column evaluation. Filter context determines the active filters for an expression. They are related but not interchangeable.

CALCULATE can perform context transition where relevant, converting row context into filter context. Explain the surrounding expression before claiming that every use of CALCULATE is doing the same kind of transition.

Why can a total differ from adding visible rows?

A total evaluates the measure in the total's context. For a ratio, that usually means calculating the ratio from the totals, not adding individual percentages. This is often correct behavior rather than a broken total.

If the business actually requires an aggregation of per-row calculations, express that requirement deliberately with the appropriate iterator and grain. First clarify the intended meaning of the total.

How would you test the answer?

  • Check no selection, North, South and both regions.
  • Show numerator and denominator next to the share.
  • Add a date filter and confirm the denominator keeps it.
  • Compare dimension and fact-column filtering.
  • Test a zero or blank denominator according to the chosen reporting rule.

Use the small fixture to explain why each result appears. Then apply the same reasoning to a larger model. A correct formula without a clear filter-context explanation is difficult to debug when report behavior changes.

References and next practice

learn.microsoft.com — bi dax · learn.microsoft.com — bi model

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