PHP+MYSQL，注销时，保存最后登陆的IP及时间，代码为何未生效？

//-----------注销begin------------------------------------------
if ( $_GET['action'] == "logout" )
{
    //注销前，记录最后一次成功登陆的IP及日期
    include('conn.php');
    $client_ip = $_SERVER["HTTP_CLIENTIP"];
    $user_id = $_SESSION['user_id'];
    echo $client_ip;
    echo $user_id;
    sleep(10);
    mysql_query("update users SET user_last_log_ip = $client_ip,user_last_log_date = unix_timestamp(now()) where user_id = $user_id limit 1");
    mysql_close($con);

     //删除SESSION
    unset($_SESSION['user_id']);
    unset($_SESSION['user_email']); 
    unset($_SESSION['user_nickname']); 
    echo '<br>'.'注销成功！';
    exit;
}

这个我建议是把sql语句打印出来，然后去mysql里面执行一下