做地址管理时,需要先根据要设为默认的地址的用户将用户的其他地址都设置为非默认

需要select出用户id然后update

原语句

update address set isdeafult = 0 where user_id = (select user_id from address where id = ?)

报错 -- You can't specify target table 'address' for update in FROM clause

 

大意是不能先select出同一表中的某些值，再update这个表(在同一语句中)

修改后的语句如下

UPDATE address a INNER JOIN (SELECT user_id FROM address WHERE id = #{id}) c SET a.isdeafult = 0 WHERE a.user_id = c.user_id

解析

select * from address a INNER JOIN

(SELECT user_id FROM address WHERE id = 1) c WHERE a.user_id = c.user_id

的内容完全等于 select * from address ,本质上就是用inner join做了个中间表查询

 

注 : 只有在mysql中才有这个错误