//执行SQL语句
    if(mysql_query($sql))
    {
      //设定Cookie值，设置1天后失效
      setcookie("visited", true, time()+3600*24);
     echo 'var recorded = true; alert($ip);';
    }
    else  //插入失败
    {
      //设定Cookie值，失效时间为过去，即删除该Cookie
      setcookie("visited", false, time()-3600*24);
      echo 'var recorded = false; alert($ip);';
    }