MySQL出现You can‘t specify target table for update in FROM clause错误的解决方法

分析原因
在MySQL中，可能会遇到You can't specify target table '表名' for update in FROM clause这样的错误

它的意思是说，不能在同一语句中，先select出同一表中的某些值，再update这个表，即不能依据某字段值做判断再来更新某字段的值。

这个问题在MySQL官网中有提到解决方案：MySQL-UPDATE- 拉到文档下面

例如下面这张t_message表

+----+-----+-----------+---------------------+
| id | uid | content   | addtime             |
+----+-----+-----------+---------------------+
|  1 |   1 | content1  | 2022-04-26 00:00:01 |
|  2 |   2 | content2  | 2022-04-26 00:00:02 |
|  3 |   3 | content3  | 2022-04-26 00:00:03 |
|  4 |   1 | content4  | 2022-04-26 00:00:04 |
|  5 |   3 | content5  | 2022-04-26 00:00:05 |
|  6 |   2 | content6  | 2022-04-26 00:00:06 |
|  7 |   2 | content7  | 2022-04-26 00:00:07 |
|  8 |   4 | content8  | 2022-04-26 00:00:08 |
|  9 |   4 | content9  | 2022-04-26 00:00:09 |
| 10 |   1 | content10 | 2022-04-26 00:00:10 |
+----+-----+-----------+---------------------+

我想将每个用户第一条消息的内容更新为Hello World

UPDATE t_message  SET content = 'Hello World'  WHERE id IN (  			 SELECT min(id) FROM t_message GROUP BY uid  			);   -- 会出现如下错误 -- ERROR 1093: You can't specify target table 't_message' for update in FROM clause   -- 解决方法：select 的结果再通过一个中间表 select 多一次，就可以避免这个错误  UPDATE message  SET content = 'Hello World'  WHERE id IN (  			SELECT min_id FROM (  				  SELECT min(id) AS min_id FROM t_message GROUP BY uid  								) AS a  			);    -- 更新的其他方式  update fa_info fb, (   select      fb.member_id as oldMemberId,      mc.id as newMemberCardId   from      fa_info fb     inner join ott_member m on fb.member_id = m.id and m.is_deleted = 0     left join ott_card c on m.idcard_no = c.idcard_no and m.type = c.type and c.is_deleted = 0     inner join ott_member_card mc on mc.member_id = m.id and (mc.card_id = c.id or mc.card_id is null) and mc.is_deleted = 0 ) mm  set fb.member_id = mm.newMemberCardId where mm.oldMemberId = fb.member_id;