PHPで従業員の残業管理機能を実装するにはどうすればよいですか?

<?php
$servername = "localhost";
$username = "your_username";
$password = "your_password";
$dbname = "your_database_name";

$conn = new mysqli($servername, $username, $password, $dbname);

if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

<form action="add_overtime.php" method="post">
    <label for="date">加班日期:</label>
    <input type="date" id="date" name="date" required><br><br>
  
    <label for="hours">加班时长:</label>
    <input type="number" id="hours" name="hours" min="0" max="24" step="0.5" required><br><br>
  
    <label for="reason">加班原因:</label>
    <textarea id="reason" name="reason" required></textarea><br><br>
  
    <input type="submit" value="提交">
</form>

<?php
$date = $_POST['date'];
$hours = $_POST['hours'];
$reason = $_POST['reason'];

$sql = "INSERT INTO overtime (employee_id, date, hours, reason) VALUES (1, '$date', '$hours', '$reason')";

if ($conn->query($sql) === TRUE) {
    echo "加班记录添加成功";
} else {
    echo "加班记录添加失败: " . $conn->error;
}

$conn->close();
?>

<?php
$sql = "SELECT * FROM overtime WHERE employee_id = 1";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    echo "<table><tr><th>加班日期</th><th>加班时长</th><th>加班原因</th></tr>";
    
    while($row = $result->fetch_assoc()) {
        echo "<tr><td>".$row["date"]."</td><td>".$row["hours"]."</td><td>".$row["reason"]."</td></tr>";
    }
    
    echo "</table>";
} else {
    echo "该员工没有加班记录";
}

$conn->close();
?>