Expressions that yield variant data-type cannot be used to define calculated columns.

[Robert4049]

I'm not really sure, why this is throwing this? I'm grabbing the earliest time?

ERFTime = 
IF (
    COUNTROWS (
        FILTER (
            RELATEDTABLE ( 'Apparatus Responses' ),
            'Apparatus Responses'[cancelledDateTime] <> BLANK ()
        )
    ) = 0,
    DATEDIFF (
        CALCULATE (
            MIN ( 'Apparatus Responses'[alarmDateTime] ),
            FILTER (
                'Apparatus Responses',
                'Apparatus Responses'[incidentID] = 'Incident Metadata'[incidentID]
            )
        ),
        CALCULATE (
            MAX( 'Apparatus Responses'[cancelledDateTime] ),
            FILTER (
                'Apparatus Responses',
                'Apparatus Responses'[incidentID] = 'Incident Metadata'[incidentID]
            )
        ),
        SECOND
    ),
    FALSE ()
)

[HotChilli]

An IF statement has to return the same datatype from any path it follows.

That code can return different data types.

[Robert4049]

Well the datediff is returning an integer? 

[v-diye-msft]

Hi @Robert4049 ,

Yes, Datediff returns the count of interval boundaries crossed between two dates.

Best regards,

Dina Ye