how to create a new column, which tells if a value is uniquely contained in another column? : I'm working with power query language (M) for Excel, and I would like to create a new column based on a condition like: 

New_column = if [Order number] is unique, 
then "1" else "0"

How can I check uniqueness with M code? 

Order number is a column I have in my dataset (where different order numbers appear many times depending on what production phase they are in), and I would like to create a new column with dummy values 1, 0 which tells me if a the order number in the current row is unique or not (as some only undergo one production phase).