如何通过PHP实现员工休假管理功能？

$start_date = $_POST['start_date'];
$end_date = $_POST['end_date'];
$reason = $_POST['reason'];

// 确保日期格式正确
$start_date = date('Y-m-d', strtotime($start_date));
$end_date = date('Y-m-d', strtotime($end_date));

// 插入休假申请
$query = "INSERT INTO leave_applications (employee_id, start_date, end_date, reason)
          VALUES ('$employee_id', '$start_date', '$end_date', '$reason')";
$result = Mysqli_query($connection, $query);

$leave_application_id = $_POST['leave_application_id'];
$status = $_POST['status'];
$comment = $_POST['comment'];

// 更新审批记录状态和备注
$query = "UPDATE approval_records
          SET status = '$status', comment = '$comment'
          WHERE leave_application_id = '$leave_application_id'";
$result = mysqli_query($connection, $query);

$employee_id = $_SESSION['employee_id'];

// 查询员工的休假记录
$query = "SELECT a.start_date, a.end_date, r.status, r.comment
          FROM leave_applications a
          INNER JOIN approval_records r ON a.id = r.leave_application_id
          WHERE a.employee_id = '$employee_id'";
$result = mysqli_query($connection, $query);

// 显示员工的休假记录
while ($row = mysqli_fetch_assoc($result)) {
    echo "开始日期：" . $row['start_date'] . "<br>";
    echo "结束日期：" . $row['end_date'] . "<br>";
    echo "审批状态：" . $row['status'] . "<br>";
    echo "备注：" . $row['comment'] . "<br><br>";
}