在执行rollBack()函数之前，PDO如何回滚查询？

// 创建PDO对象并连接到数据库
$dsn = "mysql:host=localhost;dbname=mydatabase";
$username = "username";
$password = "password";
$pdo = new PDO($dsn, $username, $password);

// 开启事务
$pdo->beginTransaction();

try {
    // 执行数据库查询操作
    $stmt = $pdo->prepare("INSERT INTO users (name, email) VALUES (:name, :email)");
    $stmt->bindParam(':name', $name);
    $stmt->bindParam(':email', $email);

    $name = "John";
    $email = "john@example.com";
    $stmt->execute();

    // 如果出现错误，回滚查询
    if ($error) {
        $pdo->rollBack();
    } else {
        // 提交事务
        $pdo->commit();
    }
} catch (PDOException $e) {
    // 处理异常
    echo "Error: " . $e->getMessage();
}