错误信息：Every derived table must have its own alias？

Question

有A、B、C三个表，我想实现：先把A和B取合集，再将这个合集与C表取交集，也就是实现A∪B∩C，该怎么用SQL语句写呢？首先感谢liaoxw624的回答，我试了一下select x1.* from((SELECT id FROM A)UNION(SELECT id FROM B))x1INNER JOINC AS t1 ON t1.id=x1.id提示错误信息：Every derived table must have its own alias于是，我又试了一下这个：select x2.* from(((SELECT id FROM A)UNION(SELECT id FROM B))x1INNER JOINC AS t1 ON t1.id=x1.id)x2又提示说最后两行有语法错误，该怎么办呢？

Answer 1

题目太笼统，假设如下
1。3个表列结构一样（不一样也可以，但必须保证可以取到相同的列射影）
2。三个表都有相同的关键字，假设为ID
则SQL文如下
select t.* from
--A∪B==>t
(select * from A
union
select * from B)t
--A∪B∩C
inner join C
on t.ID=C.ID