DAX function

COALESCE — DAX function reference

First non-blank value.

Syntax

dax

COALESCE(<value1>, <value2> [, …])

dax

COALESCE([Sales], 0)

→ A value

dax

COALESCE([Actual Sales], [Forecast Sales], 0)

→ Actual if available, else forecast, else zero

dax

COALESCE(Customer[PreferredName], Customer[FirstName], "Unknown")

→ First non-blank name field

Cleaner than IF(ISBLANK([Sales]), 0, [Sales]).
COALESCE returns the first argument that isn’t BLANK() and accepts any number of arguments — unlike an IF/ISBLANK chain, it short-circuits, so put the cheapest or most-likely-populated expression first for performance.
It only treats DAX BLANK() as empty — an empty string "" or a literal zero is not blank and is returned as-is, so it won’t substitute for a zero the way SQL’s COALESCE substitutes for NULL unless the source value is truly blank.

From Logical & error handling