Comparing Multiple Columns for Duplicate Rows to Identify Mismatching Data

[RokuCap]

I have appended tables from 2 databases only kept the rows with duplicate values (A & B). The goal is to compare the values (Field1, Field2 and Field3) for the duplicate values in the "ID" column and identify discrepancies. Then have a conditional formula to describe which columns do not match. In the case where there are multiple mismatching columns, then this will be concatenated in the "Comment": column text e.g. "Field1 Mismatch; Field2 Mismatch".

My initial attempt involved keeping the tables separate, merging them based on the ID value and then adding conditional check columns for each field. However, due to how large these tables are, I'm trying to minimize my use of the "Merge" function.

Source	ID	Field1	Field2	Field3	Comment
Database1	A	1	Japan	Yes	Field2 Mismatch
Database2	A	1	Canada	Yes	Field2 Mismatch
Database1	B	3	Australia	No	Field1 Mismatch; Field2 Mismatch
Database2	B	1	New Zealand	No	Field1 Mismatch; Field2 Mismatch

Thanks in advance!

[ImkeF · Accepted solution]

Hi @RokuCap ,
you can try to give it a go with grouping instead:

let
  Source = Table.FromRows(
    Json.Document(
      Binary.Decompress(
        Binary.FromText(
          "i45WckksSUxKLE41VNJRcgRiEO2VWJCYB6QjU4uVYnUQaoyQ1Dgn5iWmJGJRBJJ0AmJjkOLS4pKixJxMkDq/fAyznKBm+aWWK0SlJuYk5qVAFcYCAA==", 
          BinaryEncoding.Base64
        ), 
        Compression.Deflate
      )
    ), 
    let
      _t = ((type nullable text) meta [Serialized.Text = true])
    in
      type table [Source = _t, ID = _t, Field1 = _t, Field2 = _t, Field3 = _t]
  ), 
  #"Changed Type" = Table.TransformColumnTypes(
    Source, 
    {
      {"Source", type text}, 
      {"ID", type text}, 
      {"Field1", Int64.Type}, 
      {"Field2", type text}, 
      {"Field3", type text}
    }
  ), 
  #"Grouped Rows" = Table.Group(
    #"Changed Type", 
    {"ID"}, 
    {
      {
        "Mismatches", 
        each Text.Combine(
          List.Select(
            List.Transform(
              {"Field1", "Field2", "Field3"}, 
              (l) =>
                if List.Count(List.Distinct(Table.Column(_, l))) > 1 then "Mismatch " & l else null
            ), 
            (s) => s <> null
          ), 
          ", "
        )
      }, 
      {"All", each _}
    }
  ), 
  #"Expanded All" = Table.ExpandTableColumn(
    #"Grouped Rows", 
    "All", 
    {"Source", "Field1", "Field2", "Field3"}
  )
in
  #"Expanded All"