Fixed Oracle specific failures in multicolumn joins

        # QuerySet was sent

        if hasattr(query, 'values'):

            # as_sql should throw if we are using a

            # connection on another database

            query._as_sql(connection=connection)

            if query._db and connection.alias != query._db:

                raise ValueError("Can't do subqueries with queries on different DBs.")

            query = query.values(*self.targets).query

            query.clear_ordering(True)

        query_compiler = query.get_compiler(connection=connection)

        return query_compiler.as_subquery_condition(self.alias, self.columns)