There are multiple issues:
- Table rows had not been closed (</tr>)
- Usage of mysql_*functions is deprecated in PHP 5 and removed in PHP 7; if you're writing new code, you should not be usingmysql_*functions. Instead, usemysqli_*functions or the PDO library.
- There were multiple for-loops to get records, but it would create new tables each iteration.
- The table attribute "cellspacing" was misspelled.
- The results object where they are stored can either be a resource or false.
Given these, I've made the following changes that will fix the above problems:
<?php
// I've commented out the connect.php file inclusion to highlight the change to how
// you'd connect to the MySQL database using mysqli_* instead of mysql_*. I'm guessing
// as to the contents of connect.php, but this should still highlight what needs to be
// done
// include('connect.php');
$db_connection = mysqli_connect('host', 'user', 'pass', 'database_name');
$employee_results = mysqli_query($db_connection, "SELECT id,username FROM user ORDER BY id");
?>
<html>
<body>
<table width="600" border="1" cellpadding="1" cellspacing="1">
    <tr>
        <th class="active">ID</th>
        <th class="active">Name</th>
    </tr>
    <?php if ($employee_results === false): ?>
        <tr>
            <td colspan="2">No users</td>
        </tr>
    <?php else: ?>
        <?php while ($employee = mysqli_fetch_assoc($employee_results)): ?>
            <tr>
                <td><?= $employee['id'] ?></td>
                <td><?= $employee['username'] ?></td>
            </tr>
        <?php endwhile ?>
    <?php endif ?>
</table>
</body>
</html>