php - what's wrong with this simple fetch PDO statement? -

what's wrong pdo code? doesn't give me results although there results in tip table in database.

try{     $this->pdo = new pdo( "mysql:host=".zconfig::read('hostname').";dbname=".zconfig::read('database'), zconfig::read('username'), zconfig::read('password'),  zconfig::read('drivers'));     $this->pdo->setattribute(pdo::attr_errmode, pdo::errmode_exception);     $stmt = $this->pdo->prepare("select tip_text tip product_id=:product_id , item :which");         $stmt->execute(array(':product_id'   => $id, ':which' => $which  ));          $row = $stmt->fetch(pdo::fetch_assoc);             if($row['tip_text']!='') echo $row['tip_text'];             else echo "";     }     catch(pdoexception $e)       {  echo 'error: ' . $e->getmessage();   } 

and can print out final query pdo executes? (parameters included)? variables $id , $which correctly populated above.