如何高效利用PHP评论源码增强网站互动性？

<?php
// 连接数据库
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn>connect_error) {
    die("连接失败： " . $conn>connect_error);
}
// 用户注册
if (isset($_POST['register'])) {
    $username = $_POST['username'];
    $password = $_POST['password'];
    $email = $_POST['email'];
    $sql = "INSERT INTO users (username, password, email) VALUES ('$username', '$password', '$email')";
    if ($conn>query($sql) === TRUE) {
        echo "注册成功";
    } else {
        echo "Error: " . $sql . "<br>" . $conn>error;
    }
}
// 用户登录
if (isset($_POST['login'])) {
    $username = $_POST['username'];
    $password = $_POST['password'];
    $sql = "SELECT * FROM users WHERE username='$username' AND password='$password'";
    $result = $conn>query($sql);
    if ($result>num_rows > 0) {
        session_start();
        $_SESSION['username'] = $username;
        echo "登录成功";
    } else {
        echo "用户名或密码错误";
    }
}
// 发表评论
if (isset($_POST['submit_comment']) && isset($_SESSION['username'])) {
    $comment = $_POST['comment'];
    $username = $_SESSION['username'];
    $sql = "INSERT INTO comments (username, comment) VALUES ('$username', '$comment')";
    if ($conn>query($sql) === TRUE) {
        echo "评论成功";
    } else {
        echo "Error: " . $sql . "<br>" . $conn>error;
    }
}
// 显示评论
$sql = "SELECT * FROM comments";
$result = $conn>query($sql);
if ($result>num_rows > 0) {
    while($row = $result>fetch_assoc()) {
        echo "<div><strong>" . $row["username"] . "</strong>: " . $row["comment"] . "</div>";
    }
} else {
    echo "暂无评论";
}
$conn>close();
?>

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