Warning: mysql_query() expects parameter 2 to be resource, string given
in /var/www/xxxxx/data/www/xxxxx.ru/xxxxx/classes/mysql.class.php on line 51
  public function query($query, $comment = "") {
    if ($this -> conn) {
        $this -> conn = $this -> connect();
    }
    $start = microtime();
    if (!($result = mysql_query($query, $this -> conn)))  // <<-- line 51
    {
        exit(mysql_error());
    }
    $end*emphasized text* = microtime();
这里有什么问题?