Fixed #20014 -- implemented get_key_columns() for Oracle

            relations[row[0]] = (row[2], row[1].lower())

        return relations

    def get_key_columns(self, cursor, table_name):

        cursor.execute("""

            SELECT ccol.column_name, rcol.table_name AS referenced_table, rcol.column_name AS referenced_column

            FROM user_constraints c

            JOIN user_cons_columns ccol

              ON ccol.constraint_name = c.constraint_name 

            JOIN user_cons_columns rcol

              ON rcol.constraint_name = c.r_constraint_name 

            WHERE c.table_name = %s AND c.constraint_type = 'R'""" , [table_name.upper()])

        return [tuple(cell.lower() for cell in row) 

                for row in cursor.fetchall()]

    def get_indexes(self, cursor, table_name):

        sql = """

    SELECT LOWER(uic1.column_name) AS column_name,