Append different columns from one table

HI, Anonymous 

The best way is Unpivot the columns in Edit Queries.

For example:

In Edit Queries, Selected Column B,C,D.

Then click Transform->Unpivot Columns

Now remove Attribute column.

Result:

here is M colde, please try it.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45W8srPyFPSUfLNzE4FUYlF2UAqKD+pMk8pVicaKFBalAgUcUlNApJemblAMgRIxsYCAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [A = _t, B = _t, C = _t, D = _t]),
    #"Unpivoted Columns" = Table.UnpivotOtherColumns(Source, {"A"}, "Attribute", "Value"),
    #"Removed Columns" = Table.RemoveColumns(#"Unpivoted Columns",{"Attribute"})
in
    #"Removed Columns"

Best Regards,

Lin