Comment utiliser ORDER BY RAND ?

          public function findAllMedefPresentsAtEvent($event)
                  {
                      return $this->getEntityManager()
                      ->createQuery(
                        'SELECT o FROM PresenceStoreBundle:Organization o, PresenceStoreBundle:EventOrganization p WHERE p.event = :event AND p.organization = o.id AND (o.typeOrga = :typeMR OR o.typeOrga = :typeMT) ORDER BY Rand()')
                      ->setParameter('typeMR' , 'MR')
                      ->setParameter('typeMT' , 'MT')
                      ->setParameter('event' , $event)
                      ->getResult();

                  }