The expression refers to multiple columns. Multiple columns cannot be converted to a scalar value.

Hi proavinash ,

The error occurs because UNION() only accepts two tables at a time, but you're passing in three ADDCOLUMNS() results directly. DAX cannot interpret more than two tables unless you nest the UNION() calls. To fix it, you need to combine the second and third ADDCOLUMNS() calls using UNION() first, then combine that result with the first one. Here's the corrected version of your DAX:

MTD/QTD/YTD =
var TodayDate = TODAY()
var startyear = CALCULATE(STARTOFYEAR(SaleDump[Date].[Date]), YEAR(SaleDump[Date]) = YEAR(TodayDate))
var startquarter = CALCULATE(STARTOFQUARTER(SaleDump[Date].[Date]), YEAR(SaleDump[Date]) = YEAR(TodayDate), QUARTER(SaleDump[Date]) = QUARTER(TodayDate))
var startmonth = CALCULATE(STARTOFMONTH(SaleDump[Date].[Date]), YEAR(SaleDump[Date]) = YEAR(TodayDate), MONTH(SaleDump[Date]) = MONTH(TodayDate))
var result =
    UNION(
        ADDCOLUMNS(CALENDAR(startyear, TodayDate), "Selection", "YTD"),
        UNION(
            ADDCOLUMNS(CALENDAR(startquarter, TodayDate), "Selection", "QTD"),
            ADDCOLUMNS(CALENDAR(startmonth, TodayDate), "Selection", "MTD")
        )
    )
RETURN
    result

This corrects the structure so each UNION() has exactly two inputs and avoids the scalar value conversion error.

Best regards,