如何使用PHP实现邮箱验证码的自动过期功能

<?php
// 生成随机的验证码
$verificationCode = mt_rand(100000, 999999);

// 将验证码保存到数据库
$conn = new mysqli('localhost', 'username', 'password', 'database');
$stmt = $conn->prepare("INSERT INTO verification_codes (email, code, expiry_time) VALUES (?, ?, ?)");
$stmt->bind_param("sss", $email, $verificationCode, date("Y-m-d H:i:s", strtotime("+10 minutes"))); // 过期时间为当前时间后10分钟
$stmt->execute();
$stmt->close();
$conn->close();

// 将验证码发送至用户邮箱
$emailSubject = "邮箱验证码";
$emailContent = "您的验证码为：" . $verificationCode . "，该验证码将在10分钟内过期，请及时输入。";
mail($userEmail, $emailSubject, $emailContent);
?>

<?php
// 验证用户输入的验证码是否有效
$conn = new mysqli('localhost', 'username', 'password', 'database');
$stmt = $conn->prepare("SELECT * FROM verification_codes WHERE email = ? AND code = ? AND expiry_time > ? LIMIT 1");
$stmt->bind_param("sss", $email, $verificationCode, date("Y-m-d H:i:s")); // 只查询未过期的验证码
$stmt->execute();
$result = $stmt->get_result();

if ($result->num_rows == 1) {
    // 验证码有效，做相应处理
    // ...
} else {
    // 验证码无效或已过期，给出相应提示
    // ...
}

$stmt->close();
$conn->close();
?>