Edit table sql chatbox

if (isset($_GET['supprimer_message']))  
{ 
    $_GET['supprimer_message'] = addslashes($_GET['supprimer_message']); 
 { 
 mysql_query('DELETE FROM chat'); 
 } 
 else { mysql_query('DELETE FROM chat 
 WHERE id=\'' . $_GET['supprimer_message'] . '\''); } 
} 

$retour = mysql_query('SELECT * FROM chat ORDER BY id DESC');