login and logout,php

<?php

        session_start();
        if(!session_is_registered('username')) {
                header("Location: http://localhost/practice.com/?page=log-on");
        }
        
        $sessionid = $_SESSION['username'];
        $query = "SELECT * FROM ph_users WHERE username = '$sessionid'";
        $result = mysql_query($query);
        $row = mysql_fetch_array($result);
        ?>
<p>You can View Your Infomation Below:</p>
<p>Your UserName: <?php echo $row['username']; ?></p>
<p>Your Password: <?php echo $row['password']; ?></p>
<p>Your Name: <?php echo $row['fullname']; ?></p>
<p>Your Profile:<br><?php echo $row['profile']; ?></p>
<p>Your Email Address: <?php echo $row['email']; ?></p>
<p><a href="?page=logout">LogOut</a></p>