LAST COLUMN OF OLD PK

Rules we cannot skip sorting:
  1. Removing existing PK columns somewhere else than at the end of the PK;
  2. Adding existing columns to the PK, except at the end of the PK when no
     columns are removed from the PK;
  3. Changing the order of existing PK columns;
  4. Decreasing the prefix length just like removing existing PK columns
     follows rule(1), increasing the prefix length just like adding existing
     PK columns follows rule(2).

Reviewed-by: Marko Mäkelä <marko.makela@oracle.com>
Reviewed-by: Thirunarayanan Balathandayuth <thirunarayanan.balathandayuth@oracle.com>
RB: 10002