/** {@inheritDoc} */
 public function walkGroupByClause($groupByClause)
 {
     $sql = parent::walkGroupByClause($groupByClause);
     // Gets the query
     $query = $this->getQuery();
     if ($query->getHint('mysqlWalker.withRollup') === true) {
         // Appends the WITH ROLLUP modifier
         $sql .= ' WITH ROLLUP';
     }
     return $sql;
 }
 /**
  * {@inheritDoc}
  */
 public function walkGroupByClause($groupByClause)
 {
     $result = parent::walkGroupByClause($groupByClause);
     return $this->replace($this->replacements, $result);
 }