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

[MohamedAtef]

I'm trying to get the number of tickets per operator 

so i tried to use group by but it gives me this error every single time

[v-yalanwu-msft · Accepted solution]

Hi, @MohamedAtef ;

As mentioned , The GROUPBY function returns a table. So if grouping you can use the allexcept() function; Convert the above formula to the following format：

Number =
CALCULATE (
    COUNT ( Dim_Operator[Operator_Key),allexcept(Dim_Operator,Dim_Operator[Operator1] )
)

 
Best Regards,
Community Support Team _ Yalan Wu
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.

[AlexisOlson]

A measure can only output a single value. The GROUPBY function returns a table.