会话没有跟进到下一个网页

我在试图修复第二页上的会话时遇到问题。问题是，我可以在不登录的情况下导航到下一个页面，这一定意味着我没有正确使用会话

这是登录页面：

<?php
    session_start();
    $con = mysqli_connect("localhost","root","","user");
    if ( isset($_POST['username'],$_POST['password']) ) {
        $username = mysqli_real_escape_string($con, $_POST['username']);
        $password = mysqli_real_escape_string($con, $_POST['password']);
        $select_user = "SELECT * FROM user WHERE Username = '$username' AND password ='$password'";
        $run_user = mysqli_query($con, $select_user);
        $check_user = mysqli_num_rows($run_user);
        if ( $check_user > 0 ) {
        $_SESSION['User']= $username;       
        header('location:ConnectionTest.php');
        }
        else {
            echo "wrong username/password";
        }
        mysqli_close($con);
    }
?>

这是登录页面将导航到的页面

<?php
session_start();
    if ( !isset($_SESSION['User']) ) {
        header('location:login.php');
    }
    $con = new mysqli("localhost", "root", "", "schema");
    $result = $con->query("SHOW TABLES");
    while ( $row = $result->fetch_row() ) {
        $table = $row[0];
        echo '<h3>',$table,'</h3>';
        $result1 = $con->query("SELECT * FROM $table");
            if ($result1) {
                echo '<table cellpadding="0" cellspacing="0" class="db-table">';
                    $column = $con->query("SHOW COLUMNS FROM $table");
                    echo '<tr>';
                        while($row3 = $column->fetch_row()) {
                        echo '<th>'.$row3[0].'</th>';
                        } //endwhile $row3
                    echo '</tr>';
                    while($row2 = $result1->fetch_row() ) {
                    echo '<tr>';
                        foreach($row2 as $key=>$value) {
                        echo '<td>',$value,'</td>';
                        } //endforeach
                    echo '</tr>';
                    } //endwhile $row2
                echo '</table><br />';
            } //endif
    } //endwhile $row
$con->close();
?>