CREATE TABLE IF NOT EXISTS `users` (
  `id` INT AUTO_INCREMENT PRIMARY KEY,
  `username` VARCHAR(50) NOT NULL UNIQUE,
  `email` VARCHAR(100) NOT NULL UNIQUE,
  `password` VARCHAR(255) NOT NULL,
  `role` ENUM('client', 'instructor', 'manager', 'admin') NOT NULL DEFAULT 'client',
  `created_at` TIMESTAMP DEFAULT CURRENT_TIMESTAMP
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;