PHP で従業員のチェックインおよびチェックアウト機能を実装するにはどうすればよいですか?

CREATE TABLE employees (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(100) NOT NULL,
    position VARCHAR(100) NOT NULL
);

CREATE TABLE checkinout (
    id INT PRIMARY KEY AUTO_INCREMENT,
    employee_id INT NOT NULL,
    checkin DATETIME NOT NULL,
    checkout DATETIME
);

<?php
// 连接到数据库
$servername = "localhost";
$username = "your_username";
$password = "your_password";
$dbname = "attendance";

$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// 导入表格
$sql = "CREATE TABLE IF NOT EXISTS employees (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(100) NOT NULL,
    position VARCHAR(100) NOT NULL
)";

if ($conn->query($sql) === FALSE) {
    echo "创建员工表格失败: " . $conn->error;
}

$sql = "CREATE TABLE IF NOT EXISTS checkinout (
    id INT PRIMARY KEY AUTO_INCREMENT,
    employee_id INT NOT NULL,
    checkin DATETIME NOT NULL,
    checkout DATETIME
)";

if ($conn->query($sql) === FALSE) {
    echo "创建签到签退记录表格失败: " . $conn->error;
}
?>

<form action="index.php" method="post">
    <label for="name">姓名:</label>
    <input type="text" id="name" name="name" required>
    <br>
    <label for="position">职位:</label>
    <input type="text" id="position" name="position" required>
    <br>
    <input type="submit" value="添加员工">
</form>

<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $name = $_POST["name"];
    $position = $_POST["position"];

    $sql = "INSERT INTO employees (name, position) VALUES ('$name', '$position')";

    if ($conn->query($sql) === FALSE) {
        echo "添加员工失败: " . $conn->error;
    }
}
?>

<table>
    <tr>
        <th>ID</th>
        <th>姓名</th>
        <th>职位</th>
        <th>操作</th>
    </tr>
    <?php
    $sql = "SELECT * FROM employees";
    $result = $conn->query($sql);

    if ($result->num_rows > 0) {
        while ($row = $result->fetch_assoc()) {
            echo "<tr>";
            echo "<td>" . $row["id"] . "</td>";
            echo "<td>" . $row["name"] . "</td>";
            echo "<td>" . $row["position"] . "</td>";
            echo "<td><a href='checkinout.php?employee_id=" . $row["id"] . "'>签到/签退</a></td>";
            echo "</tr>";
        }
    } else {
        echo "<tr><td colspan='4'>暂无员工信息</td></tr>";
    }
    ?>
</table>

<?php
// 获取员工ID
$employee_id = $_GET["employee_id"];

// 如果是签到操作
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    date_default_timezone_set('Asia/Shanghai');
    $checkin = date("Y-m-d H:i:s");
    
    $sql = "INSERT INTO checkinout (employee_id, checkin) VALUES ('$employee_id', '$checkin')";
    
    if ($conn->query($sql) === FALSE) {
        echo "签到失败: " . $conn->error;
    }
}

// 如果是签退操作
if ($_SERVER["REQUEST_METHOD"] == "PUT") {
    date_default_timezone_set('Asia/Shanghai');
    $checkout = date("Y-m-d H:i:s");
    
    $sql = "UPDATE checkinout SET checkout='$checkout' WHERE employee_id='$employee_id' AND checkout IS NULL ORDER BY checkin DESC LIMIT 1";
    
    if ($conn->query($sql) === FALSE) {
        echo "签退失败: " . $conn->error;
    }
}

header("Location: index.php");
?>