/**
  * Returns translated group by fields with out the 'GROUP BY'
  * 
  * @param Tx_PtExtlist_Domain_QueryObject_Query $query
  * @return string group by part
  */
 public static function getGroupBy(Tx_PtExtlist_Domain_QueryObject_Query $query)
 {
     $groupByString = implode(', ', $query->getGroupBy());
     return $groupByString;
 }