mysql error 1093（HY000） You can‘t specify target table ‘xx‘ for update in FROM clause

错误代码：

update sc set grade = grade * 1.1
where sno in(select sno from sc group by sno having avg(grade)>=75);

报错详情

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

该报错意思如下：
	不能在update更新一张表的时候，同时在子查询中使用（查询 / 筛选）该表。

解决方法

设立双层子查询，让程序的执行逻辑产生先后顺序，以便正常运行，写法如下：

update sc set grade = grade * 1.1
where sno in(select * from (select sno from sc group by sno having avg(grade)>=75)as temp);