如何使用PHP实现用户评论功能

CREATE TABLE comments (
    id INT AUTO_INCREMENT PRIMARY KEY,
    content TEXT,
    username VARCHAR(50),
    created_at DATETIME
);

<?php
// 连接数据库
$mysqli = new mysqli('localhost', 'username', 'password', 'database');
if ($mysqli->connect_errno) {
    die('连接失败：' . $mysqli->connect_error);
}

// 查询评论数据
$result = $mysqli->query('SELECT * FROM comments ORDER BY created_at DESC');
if (!$result) {
    die('查询失败：' . $mysqli->error);
}

// 循环遍历评论数据，生成评论列表
while ($row = $result->fetch_assoc()) {
    echo '<div>';
    echo '<p>用户名：' . $row['username'] . '</p>';
    echo '<p>评论内容：' . $row['content'] . '</p>';
    echo '<p>发布时间：' . $row['created_at'] . '</p>';
    echo '</div>';
}

// 释放资源
$result->free();
$mysqli->close();
?>

<?php
// 连接数据库
$mysqli = new mysqli('localhost', 'username', 'password', 'database');
if ($mysqli->connect_errno) {
    die('连接失败：' . $mysqli->connect_error);
}

// 检查是否有提交评论的表单数据
if (isset($_POST['username']) && isset($_POST['content'])) {
    // 准备插入评论数据的SQL语句
    $stmt = $mysqli->prepare('INSERT INTO comments (content, username, created_at) VALUES (?, ?, NOW())');
    $stmt->bind_param('ss', $_POST['content'], $_POST['username']);

    // 执行SQL语句
    if (!$stmt->execute()) {
        die('插入失败：' . $stmt->error);
    }

    // 关闭语句
    $stmt->close();
}

// 释放资源
$mysqli->close();
?>

<form action="" method="post">
    <input type="text" name="username" placeholder="用户名" required>
    <textarea name="content" placeholder="评论内容" required></textarea>
    <button type="submit">发表评论</button>
</form>