SET DATEFIRST in FUNCTION

Question

I want to SET DATEFIRST in my function but it is not allowed.

SET DATEFIRST 1

I can add the code in a SP and call the SP from the function

Answer 1

If you need Monday as firstday follow this code snippet

declare @MyDate datetime = getdate()
                   select CASE WHEN DATEPART(DW,@MyDate) = 1   
                            THEN 7 
                          WHEN DATEPART(DW,@MyDate) <= 7 
                            THEN DATEPART(DW,@MyDate) - 1                            
                     END