get column name where values differ between unique rows
https://stackoverflow.com/questions/36173453/get-column-name-where-values-differ-between-two-rows
| COL | VAL1 | VAL2 |
|---|---|---|
| COL2 | XXX | bbb |
| COL3 | ZZZ | ccc |
| COL4 | YYY | ddd |
| COL | VAL1 | VAL2 |
|---|---|---|
| COL2 | XXX | bbb |
| COL3 | ZZZ | ccc |
| COL4 | YYY | ddd |