PHP에서 직원 로그인 및 로그아웃 기능을 구현하는 방법은 무엇입니까?

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");
?>