M - Created Column to Tag Duplicates

Hi diablo9083 ,

Please consider to use this query, if not works, please provide the sample data and the desired output. make sure that the data can be pasted in excel:

let
    // Step 1: Reference your existing Sales table
    #"Added Index" = Sales,  // Replace this with your starting table if needed

    // Step 2: Extract the Completed Order ID column as a list
    CompletedOrderList = Table.Column(Sales, "Completed Order ID"),

    // Step 3: Add a custom column to tag duplicates
    #"Added Custom" = Table.AddColumn(#"Added Index", "Duplicated", each 
        if List.Count(List.Select(CompletedOrderList, (x) => x = [Completed Order ID])) > 1 
        then "Duplicated" 
        else null),

    // Step 4: Filter rows to remove duplicates
    #"Filtered Rows" = Table.SelectRows(#"Added Custom", each [Duplicated] = null)
in
    #"Filtered Rows"