CREATE TABLE IF NOT EXISTS `telegram_group_links` (
  `id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
  `chat_id` BIGINT NOT NULL,
  `chat_title` VARCHAR(255) DEFAULT NULL,
  `merchant_id` INT UNSIGNED NOT NULL,
  `linked_by_user_id` BIGINT NOT NULL,
  `linked_by` ENUM('username','api_key') NOT NULL DEFAULT 'username',
  `status` TINYINT NOT NULL DEFAULT 1,
  `linked_at` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
  `unlinked_at` DATETIME DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `uk_chat_active` (`chat_id`, `status`),
  KEY `idx_merchant` (`merchant_id`),
  KEY `idx_chat` (`chat_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;