Can someone help me achive something like this:

Code:
$qadmin->query('INSERT INTO `mailmessages`(`account`, `message_id`, `box`) VALUES(0, \''.$headers->message_id.'\', \''.$box.'\') ON DUPLICATE KEY RETURN');
If there is a duplicate key, i dont want it to either insert nor update anything.. But i cant seem to find out what to put on duplicate key.. pls help