用PHP清理用户输入的最佳方法是什么？

$input = filter_input(INPUT_GET, 'username', FILTER_SANITIZE_STRING);

// PDO 示例
$pdo = new PDO('mysql:host=localhost;dbname=mydatabase', 'username', 'password');
$stmt = $pdo->prepare('SELECT * FROM users WHERE username = :username');
$stmt->bindParam(':username', $username);
$username = $_GET['username'];
$stmt->execute();

// MySQLi 示例
$mysqli = new mysqli('localhost', 'username', 'password', 'mydatabase');
$stmt = $mysqli->prepare('SELECT * FROM users WHERE username = ?');
$stmt->bind_param('s', $username);
$username = $_GET['username'];
$stmt->execute();

$input = $_GET['input'];
$safeInput = htmlspecialchars($input, ENT_QUOTES, 'UTF-8');

$email = $_GET['email'];
if (filter_var($email, FILTER_VALIDATE_EMAIL)) {
    // 邮箱格式正确
} else {
    // 邮箱格式错误
}