mysql 关联表查询，索引失效

来源表:

##示例
CREATE TABLE `order_wide` (
  `order_id` varchar(33) COLLATE utf8mb4_unicode_ci NOT NULL COMMENT '订单ID',
  `member_id` int(11) DEFAULT NULL COMMENT '用户ID',
  `content` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL COMMENT '订单标签',
  PRIMARY KEY (`order_id`),
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci COMMENT='订单大宽表'
;

## 示例
CREATE TABLE `order_tag` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT COMMENT 'ID',
  `order_id` varchar(33) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `content` varchar(255) NOT NULL DEFAULT '' COMMENT '标签内容',
  `status` tinyint(1) NOT NULL DEFAULT '1' COMMENT '1生效2失效',
  `admin_id` int(11) NOT NULL DEFAULT '0' COMMENT '添加管理员id，0表示系统',
  `is_show` tinyint(1) NOT NULL DEFAULT '1' COMMENT '1是2否 展示',
  `created_at` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '时间',
  `updated_at` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '时间',
  PRIMARY KEY (`id`),
  KEY `idx_is_show` (`is_show`),
  KEY `idx_order_id` (`order_id`),
) ENGINE=InnoDB AUTO_INCREMENT=103419 DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC COMMENT='订单标签表'
;

sql

select * from order o 
left join order_tag ot on o.order_id = ot.order_id 
where xxx  xxx

索引失效的原因

关联字段的charset和collate不同会导致索引失效