Previous month name in a empty table

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PattemManohar wrote:

ohb60  Please try this to get the previous month name 

Power Query Editor (M-Code)

= Table.AddColumn(#"Added Custom", "PrevMonth", each Date.MonthName(Date.AddMonths([hiredate],-1)))

DAX

PrevMon = FORMAT(EDATE(emp[hiredate],-1),"MMMM")

 

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Thank you for this but I can't make it work either : 

I wrote this in my new measure : 

PrevMon = FORMAT(EDATE(MAJ[Update];-1);"MMMM")

I got this error message : 

It is not possible to determine a single value for the 'Update' column of the 'Update' table. This can occur when a measurement formula refers to a column that contains many values, without specifying an aggregation such as min, max, count, or sum to obtain a single result.

Here's the code I have in my 'Update' column  : 

let
    Source = Table.FromRows({{DateTime.LocalNow()}},{"Update"})
in
    Source