mysql-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 '
'.'注销成功！';    exit;}