MariaDB查询枚举字段仅返回顺序序号而非实际值问题求助

各位好，我最近用MariaDB的时候碰到个闹心的问题，想请大家帮忙支支招。先把相关的表结构和初始化SQL贴出来：

CREATE TABLE `sales1_plan_detail` (
  `id` tinyint(3) unsigned NOT NULL AUTO_INCREMENT,
  `plan_duration` enum('12') NOT NULL,
  PRIMARY KEY (`id`));

INSERT INTO `sales1_plan_detail` (`id`, `plan_duration`) VALUES (1, '12');

CREATE TABLE `sales1_plan_country` (
  `id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
  `common_countryId` smallint(5) unsigned DEFAULT NULL,
  `plan_detailId` tinyint(3) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `common_countryId_sales1_plan_detailId` (`common_countryId`,`plan_detailId`),
  KEY `sales1_plan_detailId` (`plan_detailId`),
  CONSTRAINT `sales1_plan_country_ibfk_1` FOREIGN KEY (`plan_detailId`) REFERENCES `sales1_plan_detail` (`id`) ON UPDATE CASCADE);

INSERT INTO `sales1_plan_country` (`id`, `common_countryId`, `plan_detailId`) VALUES (1, 1, 1);

CREATE TABLE `sales1_user_plan` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `sales_userId` int(10) unsigned NOT NULL,
  `plan_countryId` smallint(5) unsigned NOT NULL,
  PRIMARY KEY (`id`)
  -- 注：原表结构内容被截断，以上为已获取到的部分
);

我现在查询sales1_plan_detail表的plan_duration字段时，发现返回的不是我插入的枚举实际值'12'，而是它的顺序序号1，这完全不符合我的预期。有没有大佬能帮我分析下这是啥原因导致的，该怎么调整才能让查询返回枚举的实际字符串值呢？

备注：内容来源于stack exchange，提问作者Computer User