首先是创建MYSQL数据库表。
 

CREATE TABLE tablename (
field type(max_length) DEFAULT 'default_value' (NOT) NULL
}

      可以使用的SQL语句。

CREATE TABLE useronline (
timestamp int(15) DEFAULT '0' NOT NULL,
ip varchar(40) NOT NULL,
file varchar(100) NOT NULL,
PRIMARY KEY (timestamp),
KEY ip (ip),
KEY file (file)
);

      下面我们开始使用PHP脚本，首先定义MYSQL的信息。

$server = "localhost"; //你的服务器
$db_user = "root"; //你的mysql的用户名
$db_pass = "password"; //你的mysql的密码
$database = "users"; //表的名字

      设置统计的时间(多少秒内在线人数)

$timeoutseconds = 300;

      取当前时间。

$timestamp = time();

      上面的完整代码：

<?php
$server = "localhost"; //your server
$db_user = "root"; //your mysql database username
$db_pass = "password"; //your mysql database password if any
$database = "users"; //the db name
$timeoutseconds = 300;//timeoutseconds limit
//get the current time
$timestamp = time();
//calculate the lowest timestamp allowed
$timeout = $timestamp-$timeoutseconds;
?>

      连接mysql

 mysql_connect('localhost', 'username', 'password');

      也允许使用变量形式。

mysql_connect($server, $db_user, $db_pass);

      如果mysql数据库没有密码的话可以使用下面代码连接（当然建议大家一定要设置好自己的密码，这样起码黑客得要解密啊）

mysql_connect($server, $db_user);

      查询数据库的代码：

mysql_db_query('database', 'query');

      我们只要有访客就要增加一条记录。

$insert = mysql_db_query($database, "INSERT INTO useronline VALUES
('$timestamp','".$_SERVER['REMOTE_ADDR']."','".$_SERVER['PHP_SELF']."')");

      然后我们给出如果用户用错误信息的处理方式。

if(!($insert)) {
print "Useronline Insert Failed > ";
}

      然后我们得实现当超过我们设置的时间我们就要删除该用户记录。

 $delete = mysql_db_query($database, "DELETE FROM useronline WHERE timestamp<$timeout");

      同样给出删除记录出错的处理。

if(!($delete)) {
print "Useronline Delete Failed > ";
}

      下面我们显示数据库中有多少个不同的IP

$result = mysql_db_query($database, "SELECT DISTINCT ip FROM useronline WHERE file='".$_SERVER['PHP_SELF']."' ");

      我们使用mysql_num_rows(query);来统计用户，代码如下:

$user = mysql_num_rows($result);

      最后我们要关闭数据库。

mysql_close();

      显示在线的人数。

if($user == 1) {
print("1 user online\n");
} else {
print("$user users online\n");
}

      最终把上面代码写成一个PHP文件如下。

<?php
//Put your basic server info here
$server = "localhost"; //normally localhost
$db_user = "root"; //your MySQL database username
$db_pass = "password"; //your MySQL database password
$database = "users";
$timeoutseconds = 300; //it will delete all people which haven't refreshed(so probbably are
// offline or inactive) in $timieoutseconds time (so it actually checks the people that are active in the last
// $timeoutseconds seconds)
//this is where PHP gets the time
$timestamp = time();
//counts the timeout, all people which have been seen last online in earlier than this timestamp, will get removed
$timeout = $timestamp-$timeoutseconds;
//connect to database
mysql_connect($server, $db_user);
//add the t