SQL 基础语法整理

update select 之后的数据

update B
set B_account = b.s_amount
from B a,
(
select sum(amount) as s_amount,pay_id from A group by pay_id
) b
where a.pay_id = b.pay_id

select name from (select name,avg(score) as a_score from student where name like '张%' group by name) a where a.a_score > 75

可以看出Mysql、Sybase、SQL SERVER的解决办法是使用UPDATE…SET…FROM…WHERE…的语法，实际上就是从源表获取更新数据。

注意：from后面是两个表的连接，源表+查询结果表。

oracle、DB2中：

UPDATE A SET (A1, A2, A3) = (SELECT B1, B2, B3 FROM B WHERE A.ID = B.ID)
WHERE ID IN (SELECT B.ID FROM B WHERE A.ID = B.ID)

UPDATE A SET (A1, A2, A3) = (SELECT B1, B2, B3 FROM B WHERE A.ID = B.ID)

可以看出，后面的查询只是查询的一张表。

注意：mysql 5.7中上面语句不好使，要这样写：

update users a left join employee b on a.users_id = b.id set a.salary = b.salary;