Allow tables/csv files to have a defined key ( multiple columns ) #3041
Description
In another very popular difference tool, it is possible to define a key field that informs the diff tool that the column must be equal, otherwise the row is not matched under any circumstances.
The file is usually sorted to perform this mode of comparison, because the order is not so important for a key-based match
The key can be a composite of a number of columns/fields, with a hierarchy initially defined as a field is marked as a key, but with some mechanism to allow the config to be changed later.