public function delete($req)
 {
     $db = new POD();
     $p = $db->connect();
     if ($p == false) {
         throw new Exception('Database connect failed');
     }
     $table = 'evaluate';
     $sql = $db->genDeleteSql($req, $table);
     $res = $db->query($sql);
     $db->close();
     return $res;
 }