php同一个用户同时只能登陆一个, 后登陆者踢掉前登陆者（排他登陆）

通常用户登陆,如果没有特别的限定, 同一个用户可以同时登陆, 今天搞了一个东西限定一个用户不能同时登陆到一个系统上, 后登陆者会把前面登陆的踢出来.(有点像QQ,同个帐号不能在多个地方同时在线, 后面登陆成功后就把前面登陆的掉线)

SQL : 两张表,一张是用户信息,另一张用来保存session

--
-- 数据库: `single_user`
--
CREATE TABLE IF NOT EXISTS `session` (
`username` varchar(50) default '',
`time` varchar(14) default '',
`session_id` varchar(200) NOT NULL default '0',
 `userid` int(11) default '0',
 PRIMARY KEY  (`session_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `users` (
`userid` int(11) NOT NULL auto_increment,
  `username` varchar(255) NOT NULL,
  `password` varchar(255) NOT NULL,
  PRIMARY KEY  (`userid`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=2 ;

数据表 session 以session_id 为主键, 这个主键是 userid + user name + user login time 的 md5值算出来的. 每次用户登陆的时候就会像session表里插入一条,同时以userid username为条件查询旧的session记录并且删除他,所以当页面判断当前用户是否有效时,是通过$_SESSION数组里面保存在session_id值和数据库里取出来的session_id进行比较, 旧的session_id 在此用户第2次登陆时已经被删除,因此找不到,从而被退出系统.

代码部分
1.config.php 一些简单的配置,包括数据库的连接

<?php
$live_site = 'testing';
$session_life = 600;
function getConnect()
{
    $db_local = 'localhost';
    $db_user = 'root';
    $db_pwd = 'root';
    $db_name = 'single_userlogin';

    $db_link = mysqli_connect($db_local, $db_user, $db_pwd,$db_name);

    if ($db_link)
    {
        return $db_link;
    }
        return false;
}

2. index.php 登陆页面

<?php
require_once('config.php');
$db = getConnect();
if (isset($_POST['username']) && isset($_POST['password']))
{
    //处理用户登陆后的数据验证
    $query = 'SELECT * FROM `users` WHERE `username`="' . trim($_POST['username']) . '" AND `password`="' .md5( trim( $_POST['password'] ) ) . '"';
    $result = mysqli_query($db,$query);

    $rs_num = mysqli_num_rows($result);

    if ($rs_num > 0 )
    {
        //该用户存在
        $row = mysqli_fetch_assoc($result);
        $userid = $row['userid'];
        $username = $row['username'];
        $logintime = time();

        //创建session_id值
        $session_id = md5( $userid . $username . $logintime );

        //登陆成功后要插入一条记录到session表中
        $sql = 'INSERT INTO session SET `time`="'.$logintime.'", `session_id`="'.$session_id.'", `userid`='.$userid.', `username`="'.$username.'"';
        mysqli_query( $db, $sql);
        echo $sql; echo "<br>";
        //并且要把session表里旧的session_id删除掉
        $query = 'DELETE FROM `session` WHERE `userid`=' . $userid . ' AND `username`="' . $username . '" AND `session_id`!="' . $session_id . '"';
        $old_session = mysqli_query($db,$query);
        echo $query;

        //开启session, 把新登陆的用户信息进入$_SESSION中
        session_name( md5( $live_site ) );
        session_id( $session_id );
        session_start();

        $_SESSION['session_id'] = $session_id;
        $_SESSION['userid'] = $row['userid'];
        $_SESSION['username'] = $row['username'];
        $_SESSION['logintime'] = $logintime;
        echo '<pre>';
        var_dump($_SESSION);
        session_write_close();
        echo '<script type="text/javascript">window.location.href="index2.php"</script>';
    } else {
        echo '<script type="text/javascript">window.location.href="index.php?mosmsg=Username Error"</script>';
    }
} else {
    //用户登陆框
    ?>
    <form method="post" name="user_login" id="user_login" action="index.php">
    Username:<input type="text" name="username" id="username" value=""/>
    <br />
    password:<input type="password" name="password" id="password" value=""/>
    <br />
    <input type="submit" name="submit" id="submit" value="Submit"/>
    </form>
<?php
}
?>

3. index2.php 用户成功登陆后需要处理原来上一次该用户的session信息, 如果上一次此用户的登陆信息还有效,需要将其删除

<?php
require_once('config.php');
$db = getConnect();
session_name( md5( $live_site ) );
session_start();

$userid = $_SESSION['userid'];
$username = $_SESSION['username'];
$logintime = $_SESSION['logintime'];
$session_id = $_SESSION['session_id'];

//判断用户是否有登陆
if ($session_id != session_id()) {
    echo "<script>document.location.href='index.php?mosmsg=Invalid Session'</script>\n";
    exit();
}
if ($session_id == md5( $userid . $username . $logintime )) {
    $past = time() - $session_life;

    //删除已经超时但是记录还存在的记录
    $query = "DELETE FROM session"
        . "\n WHERE time < '" . (int) $past . "'"
        . "\n AND userid <> 0"
        ;
    mysqli_query($db,$query);
    $current_time    = time();
    // update session timestamp 更新登陆用户的时间戳
    $query = 'UPDATE #__session'
        . '\n SET time="' .  $current_time . '"'
            . '\n WHERE session_id = "' . $session_id . '"';

    //以当前用户登陆后产生的$session_id 来查询 session表里的记录是否存在
    //如果不存在那么就跳到登陆页面
    $query = "SELECT COUNT( session_id )"
            . "\n FROM session"
            . "\n WHERE session_id = '" .  $session_id . "'"
            . "\n AND username = '". $username . "'"
            . "\n AND userid = ". $userid;
    $session_rs = mysqli_query($db,$query);
    $session_row = mysqli_fetch_row($session_rs);
    $session_num = $session_row[0];
    if ($session_num > 0 )
    {
        echo 'WELCOME<br / ><a href="logout.php">Logout</a>';
    } else {
        echo "<script>document.location.href='index.php?mosmsg=Admin Session Expired'</script>\n";
    }
} else {
    // session id does not correspond to required session format
    echo "<script>document.location.href='index.php?mosmsg=Invalid Session'</script>\n";
   exit();
}
?>

4. logout.php 退出用户,并且删除 SESSION

<?php
require_once('config.php');
$db = getConnect();
session_name( md5( $live_site ) );
session_start();

$userid = $_SESSION['userid'];
$username = $_SESSION['username'];
$logintime = $_SESSION['logintime'];
$session_id = $_SESSION['session_id'];

$sql = 'DELETE FROM session WHERE userid='.$userid.' AND username="'.$username.'" AND session_id = "'.$session_id.'"';
mysqli_query($db,$sql);
session_destroy();
echo "<script>document.location.href='index.php'</script>\n";
exit();
?>

转载：https://www.cnblogs.com/belie8/articles/2196529.html