code: @WithBridgeMethods(value = MySQLQuery.class, castRequired = true)
      public C withRollup() {
          return addFlag(Position.AFTER_GROUP_BY, WITH_ROLLUP);
      }
docs: The GROUP BY clause permits a WITH ROLLUP modifier that causes extra rows to be added to the
  summary output. These rows represent higher-level (or super-aggregate) summary operations.
  ROLLUP thus enables you to answer questions at multiple levels of analysis with a single query.
  It can be used, for example, to provide support for OLAP (Online Analytical Processing) operations.
  
  @return the current object