從A表查找數據，字段卻在B表

Question

我要从A表中查出数据，但是要显示的字段是从B表中取出的…… 
我想根據B表中的DetailID（QID=’090001’）得到A表中（QID=’090001’）對應的總分是多少？
如B表的DetailID=1就對應了A表中Detail1_Score 5分
  B表的DetailID=10就對應了A表中Detail10_Score 0分
這樣A表中QID=’090001’的總分就是5+0=5分A表相關的資料如下：
Qid,    Item_Section, Item_Group, Itemid,Detail1_Name,Detail1_Score,Detail2_Name,Detail2_Score……Detail10_Name,Detail10_Score
090001  CL               CL3      1      問題1           5         問題2            4            null                null
090001  CL               CL3      2      問題1           9         問題2            8            問題10              0B表相關的資料如下：
Qid,    Item_Section,  Item_Group,   Itemid,  DetailID
090001  CL               CL3           1       1
090001  CL               CL3           2       10

Answer 1

select sum(decode(B.DetailID,1,A.Detail1_Score,
                             2,A.Detail1_Score2,
                             3,A.Detail1_Score3,
                             4,A.Detail1_Score4,
                             5,A.Detail1_Score5,
                             6,A.Detail1_Score6,
                             7,A.Detail1_Score7,
                             8,A.Detail1_Score8,
                             9,A.Detail1_Score9,
                             10,A.Detail1_Score10)) totalScore
from A,B 
where A.Itemid=B.Itemid 

Answer 2

少了个关联条件
select sum(decode(B.DetailID,1,A.Detail1_Score,
                             2,A.Detail1_Score2,
                             3,A.Detail1_Score3,
                             4,A.Detail1_Score4,
                             5,A.Detail1_Score5,
                             6,A.Detail1_Score6,
                             7,A.Detail1_Score7,
                             8,A.Detail1_Score8,
                             9,A.Detail1_Score9,
                             10,A.Detail1_Score10)) totalScore
from A,B 
where A.Itemid=B.Itemid
amd A.Qid=B.Qid

Answer 3

select b.qid,decode(b.detailID,1,a.detail1_score,2,a.detail2_score,.......) score
from a,b 
where a.qid=b.qid

Answer 4

取合计再加个sum  group by