GROUP_CONCAT s JOINLEFT v Zend Db Select

Nepoužili jste group by klauzule v dotazu.

Zkuste níže:

$select->from(array('a'=>'articles'))
  ->joinLeft(
       array('i'=>'images'),
       'i.article_id=a.id',
       array('images'=> new Zend_Db_Expr('GROUP_CONCAT(i.image)')))
  ->group('a.id');