How to use email verification in PHP to prevent users from registering with false identities?

CREATE TABLE users (
  id INT(11) PRIMARY KEY AUTO_INCREMENT,
  username VARCHAR(50) NOT NULL,
  password VARCHAR(255) NOT NULL,
  email VARCHAR(50) NOT NULL,
  is_verified TINYINT(1) DEFAULT 0
);

<form method="post" action="register.php">
  <input type="text" name="username" placeholder="用户名" required>
  <input type="password" name="password" placeholder="密码" required>
  <input type="email" name="email" placeholder="邮箱地址" required>
  <button type="submit">注册</button>
</form>

<?php
// 连接到数据库
$conn = mysqli_connect("localhost", "username", "password", "dbname");

// 检查连接是否成功
if (!$conn) {
  die("数据库连接失败：" . mysqli_connect_error());
}

// 处理注册表单
if ($_SERVER["REQUEST_METHOD"] == "POST") {
  // 获取用户提交的注册信息
  $username = $_POST["username"];
  $password = $_POST["password"];
  $email = $_POST["email"];

  // 检查邮箱是否已经被注册
  $emailQuery = "SELECT * FROM users WHERE email = '$email'";
  $result = mysqli_query($conn, $emailQuery);

  if (mysqli_num_rows($result) > 0) {
    echo "该邮箱已被注册，请使用其他邮箱。";
  } else {
    // 生成一个随机的验证码
    $verificationCode = mt_rand(100000, 999999);

    // 将用户信息插入数据库，并设置未验证状态
    $insertQuery = "INSERT INTO users (username, password, email, is_verified) VALUES ('$username', '$password', '$email', 0)";
    mysqli_query($conn, $insertQuery);

    // 发送验证邮件
    $subject = "邮箱验证";
    $message = "您的验证码是：" . $verificationCode;
    $headers = "From: your_email@example.com";

    mail($email, $subject, $message, $headers);

    echo "请查看您的邮箱并输入验证码来完成注册。";
  }
}

// 关闭数据库连接
mysqli_close($conn);
?>

<?php
// ...
if ($_SERVER["REQUEST_METHOD"] == "POST") {
  $verificationCode = $_POST["verificationCode"];

  // 检查验证码是否正确
  $verificationQuery = "SELECT * FROM users WHERE email = '$email' AND is_verified = 0";
  $result = mysqli_query($conn, $verificationQuery);

  if (mysqli_num_rows($result) > 0) {
    $user = mysqli_fetch_assoc($result);
    if ($verificationCode == $user["verification_code"]) {
      // 更新用户状态为已验证
      $updateQuery = "UPDATE users SET is_verified = 1 WHERE email = '$email'";
      mysqli_query($conn, $updateQuery);

      echo "邮箱验证成功！";
    } else {
      echo "验证码不正确，请重新输入。";
    }
  } else {
    echo "该邮箱已经通过验证。";
  }
}
// ...
?>