Mysql You can't specify target table for update in FROM clause

1093 - You can't specify target table 'table_name' for update in FROM clause;
不能先select出同一表中的某些值，再update这个表(在同一语句中)

原语句：

delete from i_user where b_code in (
select b_code from i_user
group by b_code
HAVING count(u_code) > 1) limit 1;

修改后：即增加一个中间表作为查询结果，再删除

delete from i_user where b_code in (
select b_code from (
select b_code from i_user
group by b_code
HAVING count(u_code) > 1) t) limit 1;

该问题只会出现在：mysql

oracle 以及 sqlServer 不会出现