CREATE TABLE IF NOT EXISTS `users` (
  `id` INT AUTO_INCREMENT PRIMARY KEY,
  `username` VARCHAR(255) NOT NULL UNIQUE,
  `password` VARCHAR(255) NOT NULL,
  `email` VARCHAR(255) NOT NULL UNIQUE,
  `role_id` INT,
  `created_at` TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
  FOREIGN KEY (role_id) REFERENCES roles(id)
);