如何通过PHP编写一个简单的在线访客留言系统

CREATE TABLE messages (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(50) NOT NULL,
    email VARCHAR(50) NOT NULL,
    message TEXT NOT NULL,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

<form method="POST" action="submit.php">
    <label for="name">姓名:</label>
    <input type="text" id="name" name="name" required>
    
    <label for="email">邮箱:</label>
    <input type="email" id="email" name="email" required>
    
    <label for="message">留言:</label>
    <textarea id="message" name="message" required></textarea>
    
    <button type="submit">提交留言</button>
</form>

<?php
// 连接数据库
$db_host = '数据库主机';
$db_name = '数据库名字';
$db_user = '数据库用户名';
$db_pass = '数据库密码';
$conn = new mysqli($db_host, $db_user, $db_pass, $db_name);
if ($conn->connect_error) {
    die('数据库连接失败: ' . $conn->connect_error);
}

// 处理留言提交
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $name = $_POST['name'];
    $email = $_POST['email'];
    $message = $_POST['message'];
    
    $sql = "INSERT INTO messages (name, email, message) VALUES ('$name', '$email', '$message')";
    if ($conn->query($sql) === TRUE) {
        echo '留言提交成功';
    } else {
        echo '留言提交失败: ' . $conn->error;
    }
}

// 关闭数据库连接
$conn->close();
?>

<?php
// 连接数据库
$db_host = '数据库主机';
$db_name = '数据库名字';
$db_user = '数据库用户名';
$db_pass = '数据库密码';
$conn = new mysqli($db_host, $db_user, $db_pass, $db_name);
if ($conn->connect_error) {
    die('数据库连接失败: ' . $conn->connect_error);
}

// 查询留言列表
$sql = "SELECT * FROM messages ORDER BY created_at DESC";
$result = $conn->query($sql);

// 显示留言列表
if ($result->num_rows > 0) {
    while ($row = $result->fetch_assoc()) {
        echo '姓名: ' . $row['name'] . '<br>';
        echo '邮箱: ' . $row['email'] . '<br>';
        echo '留言: ' . $row['message'] . '<br>';
        echo '时间: ' . $row['created_at'] . '<hr>';
    }
} else {
    echo '暂无留言';
}

// 关闭数据库连接
$conn->close();
?>