Subquery in where clause ——where里面的子query
例子1： 让我们找到过去所有赛季，每个赛季获得过 Finals MVP的球员的名字和他所在的球队
直接的实现方法可以采用join，例如：
select distinct b.year, b.playerID, a.firstName, a.lastName, d.tmID, d.name
from
(select bioID, firstName, lastName
from basketball_master) a
join
(select year, playerID, award
from basketball_awards_players
where award = "Finals MVP") b
join
(select year, tmIDWinner
from basketball_series_post
where round = "F" and lgIDWinner = "NBA") c
join
(select tmID, name
from basketball_teams) d
where a.bioID = b.playerID
and b.year = c.year
and c.tmIDWinner = d.tmID
order by b.year
问题是，这个query很长，不够简洁；此外，过程当中如果出现问题，观察输出结果未必见得能发现问题。好在这个query只是输出几十年的冠军，一眼就能看出来是不是出了问题。
这个query
select * from
(select bioID, year, firstName, lastName
from basketball_awards_players , basketball_master where bioID = playerID and award = "Finals MVP") a
join
(select tmIDWinner, P. year from basketball_series_post P , basketball_teams T
where P.year = T.year and P.tmIDWinner = T.tmID and P.round = "F" and P.lgIDWinner = "NBA") b
on a.year = b.year
在where clause里面的select 只能选择一个expression
例子2：找到NBA里面在同一个区的球队。
这个query可以用join来完成：
select distinct * from
(SELECT tmID, dIvID, lgID from basketball_teams
where lgID = "NBA") a
join
(SELECT tmID, dIvID, lgID from basketball_teams where lgID = "NBA") b
where a.tmID < b.tmID and a.dIvID = b.dIvID
但是用where clause，可以更简洁一些。
SELECT distinct tmID, dIvID, lgID from basketball_teams T1
where lgID = "NBA"
and
T1.tmID in
( select tmID from basketball_teams T2 where T1.dIvID = T2.dIvID)
select distinct * from
(SELECT tmID, dIvID, lgID from basketball_teams
where lgID = "NBA") a
join
(SELECT tmID, dIvID, lgID from basketball_teams where lgID = "NBA") b
where a.tmID < b.tmID and a.dIvID = b.dIvID
group by a.tmID
order by a.dIvID
接下来我们谈一下sub query in from clause