IS NULL en COALESCE gebruiken in OrderBy Doctrine Querybuilder

misschien kan dit helpen :

$qb = $em->createQueryBuilder();
$qb->select('Entity, COALESCE(Entity.column1, Entity.column2) as columnOrder')
   ->from('Namespace\EntityName', 'Entity')
   ->addOrderBy('columnOrder', 'ASC')
   ->getQuery()
   ->execute();