Once upon a time, I was bit by a time column which straightforward equality-comparison DAX wouldn’t filter as expected. From this saga, I learned a couple important lessons about Power BI’s data types that are not intuitively obvious from the user interface.

Imagine some simple DAX like the below. When evaluated, the result I’d receive back was blank—even though rows with the matching time could be plainly seen in Power BI’s table view.

CALCULATE (
  COUNTROWS ( Data ),
  Data[Timestamp] = TIME (12, 30, 0)
)

Why this strange behavior? Turns out, Power BI’s UI was not displaying the full data values in the column. When viewed in the UI’s table view, it looked like matching values existed in the column, but actually they didn’t. Comparisons were being performed correctly, just not against the time-only values I thought were there.