Oracle SQL加11g中的多表加入查詢

Question

我有三個表。

1. 表SCHOOL：schoolcode（PK），year，schoolname。
2. 表ENROLMENT：schoolcode，一年，類名，招收
3. 表CLASS：schoolcode，今年的classid，客房

現在，我想找到的學校名單，在類名報名 - 1至4以及1-4級使用的教室數量。

我用下面的查詢：

select 
    m.schoolcode, m.schoolname, sum(e.c1+e.c2+e.c3+e.c4), sum(c.rooms) 
from 
    dise2k_enrolment09 e, dise2k_master m, dise2k_clsbycondition 
where 
    m.schoolcode = e.schoolcode 
    and m.schoolcode = c.schoolcode 
    and e.year = '2011-12' and m.year = '2011-12' and c.year = '2011-12' 
    and classid in (1,2,3,4) 
    and e.classname in (1,2,3,4) 
group by 
    m.schoolcode, m.schoolname 

但結果顯示不正確。在課堂上，入學人數遠遠高於實際人數。

Answer 1

試試這個：

select m.schoolcode, m.schoolname, sum(e.c1+e.c2+e.c3+e.c4), sum(c.rooms) 
from dise2k_enrolment09 e join dise2k_master m 
on m.schoolcode=e.schoolcode 
join dise2k_clsbycondition c 
on m.schoolcode=c.schoolcode 
where e.year='2011-12' and m.year='2011-12' and c.year='2011-12' 
and classid in(1,2,3,4) 
and e.classname in(1,2,3,4) 
group by m.schoolcode, m.schoolname 

Answer 2

試試這個：

select m.schoolcode, m.schoolname, sum(e.c1+e.c2+e.c3+e.c4), sum(c.rooms) 
from dise2k_enrolment09 e, dise2k_master m ,dise2k_clsbycondition c 
where m.schoolcode=e.schoolcode and m.schoolcode=c.schoolcode and e.year='2011-12' and m.year='2011-12' and c.year='2011-12' 
and c.classid in(1,2,3,4) 
and e.classname = c.classid 
group by m.schoolcode, m.schoolname 

的方式，你就會明白：and e.classname in(1,2,3,4)是喜歡你的where子句在具有OR操作。

(c.classid=1 or c.classid=2 or c.classid=3 or c.classid=4) 
and 
(e.classname=1 or e.classname=2 or e.classname=3 or e.classname=4) 

所以，c.classid可以是「1」，e.classname可以是「2」，這是錯誤的

UPDATE我仍然認爲問題是，你不連接c.classid與e.classname

試試這樣說：

select m.schoolcode, m.schoolname, sum(e.c1+e.c2+e.c3+e.c4), sum(c.rooms) 
from dise2k_enrolment09 e, dise2k_master m ,dise2k_clsbycondition c 
where m.schoolcode=e.schoolcode and m.schoolcode=c.schoolcode and e.year='2011-12' and m.year='2011-12' and c.year='2011-12' 
and c.classid in(1,2,3,4) 
and c.classid = decode(e.classname,1,7,2,7,3,8,4,8,5,9,6,9,7,10,8,10) 
group by m.schoolcode, m.schoolname