PHP+Mysql+jQuery counts the current number of online users

<p class="demo"> 
  <p id="total">当前在线：<span id="onlinenum"></span></p> 
  <ul id="onlinelist"> 
    <li><img src="loader.gif"></li> 
  </ul> 
</p>

.demo{width:150px; margin:20px auto; font-size:14px} 
#total{padding:6px 10px; background:#090 url(arr.png) no-repeat right top; color:#fff; 
cursor:pointer; -moz-border-radius:5px; -webkit-border-radius:5px; border-radius:5px; 
-moz-box-shadow:0 0 3px #ccc; -webkit-box-shadow:0 0 3px #ccc;box-shadow:0 0 3px #ccc;} 
#onlinelist{background:#f7f7f7; border:1px solid #d3d3d3; display:none; -moz-border-radius:5px; 
-webkit-border-radius:5px; border-radius:5px; -moz-box-shadow:0 0 3px #ccc; 
-webkit-box-shadow:0 0 3px #ccc;box-shadow:0 0 3px #ccc;} 
#onlinelist li{height:20px; line-height:20px;padding:4px 6px;border-bottom:1px dotted #d9d9d9} 
#onlinelist li span{float:right} 
#onlinelist li:hover{background:#fff}

CREATE TABLE IF NOT EXISTS `online` ( 
 `id` int(11) NOT NULL AUTO_INCREMENT, 
 `ip` varchar(30) NOT NULL, 
 `province` varchar(64) NOT NULL, 
 `addtime` int(10) NOT NULL DEFAULT '0', 
 PRIMARY KEY (`id`) 
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

include_once('connect.php'); //连接数据库 
 
$ip = get_client_ip(); //获取客户端IP 
$time = time(); 
//查询表中是否有ip为当前访客IP的记录 
$query = mysql_query("select id from online where ip='$ip'"); 
if(!mysql_num_rows($query)){//如果不存在访客IP 
  if($_COOKIE['geoData']){//如果存在cookie，则获取用户的区域 
    $province = $_COOKIE['geoData']; //区域（省份） 
  }else{ 
    $api = "http://int.dpool.sina.com.cn/iplookup/iplookup.php?format=json&ip=$ip"; 
    $json = file_get_contents($api);//
    $arr = json_decode($json,true);//解析json 
    $province = $arr['province'];//获取省份 
    setcookie('geoData',$province,$time+600); //设置cookie，设置过期时间为10分钟 
  } 
  //将访客信息插入到数据表中 
  mysql_query("insert into online (ip,province,addtime) values ('$ip','$province','$time')"); 
}else{//如果存在，则更新该用户访问时间 
  mysql_query("update online set addtime='$time' where ip='$ip'"); 
} 
//删除已过期的记录 
$outtime = $time-600; 
mysql_query("delete from online where addtime<$outtime"); 
//统计总记录数，即在线用户数 
list($totalOnline) = mysql_fetch_array(mysql_query("select count(*) from online")); 
echo $totalOnline;//输出在线总数 
mysql_close();

function get_client_ip() { 
  if (getenv("HTTP_CLIENT_IP") && strcasecmp(getenv("HTTP_CLIENT_IP"), "unknown")) 
    $ip = getenv("HTTP_CLIENT_IP"); 
  else if (getenv("HTTP_X_FORWARDED_FOR") && strcasecmp(getenv("HTTP_X_FORWARDED_FOR"), 
"unknown")) 
    $ip = getenv("HTTP_X_FORWARDED_FOR"); 
  else if (getenv("REMOTE_ADDR") && strcasecmp(getenv("REMOTE_ADDR"), "unknown")) 
    $ip = getenv("REMOTE_ADDR"); 
  else if (isset ($_SERVER['REMOTE_ADDR']) && 
$_SERVER['REMOTE_ADDR'] && strcasecmp($_SERVER['REMOTE_ADDR'], "unknown")) 
    $ip = $_SERVER['REMOTE_ADDR']; 
  else 
    $ip = "unknown"; 
  return ($ip); 
}

include_once('connect.php');//连接数据库 
//查询区域统计 
$sql = "select province,count(*) as total from online group by province order by total desc"; 
$result = mysql_query($sql); 
while($row=mysql_fetch_array($result)){ 
  $list[] = array( 
    'province' => $row['province'], 
    'total' => $row['total'] 
  );  
} 
echo json_encode($list);//以json格式输出

$(function(){ 
  $("#onlinenum").load("online.php"); 
   
  $(".demo").hover(function(){ 
    $("#onlinelist").slideDown("fast"); 
    var str = ''; 
    $.getJSON("geo.php",function(json){ 
      $.each(json,function(index,array){ 
        str = str + "<li><span>"+array[&#39;total&#39;]+"</span>"+array[&#39;province&#39;]+"</li>"; 
      }); 
      $("#onlinelist").html(str); 
    }); 
  },function(){ 
    $("#onlinelist").slideUp("fast"); 
  }); 
});