数据库表的别名及应用

一个复杂的查询：

--取出State = 2 and Grade = 0、User数量>=3、ticket = 1、ticket数量>=2的

SELECT a.ID,a.Name
FROM
(
select ID ,Name from TB1
where State = 2 and Grade = 0
) a ,
(

select ID ,count(User) AS NUM from TB2
group by ID
having count(User) >= 3
)
 b ,
(
select ID ,count(ticket) AS NUM from TB2
where ticket = 1
group by ID
having count(ticket) >= 2
)

 c
WHERE a.ID = b.ID and b.ID = c.ID