Zend_Db_Select中的ifnull

Question

请给我帮助。要完成此功能以显示所有j2表，但是如果$ nom_entrepot_client为null，则不执行j2.nom条件；如果不为null，则执行条件。

这是我的代码

 public static function getlignes($pagenumber,$code,$nom_magasin,$nom_entrepot_client,$nom,$id_ville,$results){
    $db = Zend_Db_Table::getDefaultAdapter();
    $data = new Zend_Db_Select($db);


    $select = $db->select()
             ->from(array('t' => 'clients'),
                        array('id_client',
                            'code',
                            'nom_magasin',
                            'CONCAT(t.nom," ",t.prenom) as client',
                            'fixe',
                            'mobile',
                            'fax'))
                 ->join(array('j1' => 'villes'),
                        'j1.id_ville = t.id_ville',
                        array('nom as nom_ville'))
                ->joinleft(array('j2' => 'entrepots_client'),
                        't.id_client = j2.id_client',
                        array('nom as nom_entrepot_client'))
                 ->where('t.code like ?',($code==null)? '%':$code)
                 ->where('t.nom like ?',($nom==null)? '%':$nom)
                 ->where('t.nom_magasin like ?',($nom_magasin==null)? '%':$nom_magasin)
                 **->where('j2.nom like ?',($nom_entrepot_client==null)? '%':$nom_entrepot_client)**
                 ->where('t.id_ville like ?',((($id_ville==0)?null:$id_ville)==null)? '%':$id_ville)
                 ->order(array('nom_ville','nom_magasin'));

    $page = Zend_Paginator::factory($select);
    $page->setCurrentPageNumber($pagenumber/$results+1);
    $page->setItemCountPerPage($results);
    return $page;

}