Sql Query：無法對來自不同表格的數據進行分組

Question

我無法解析此查詢。

表是：

tblStandard1students 
tblStandard2students 
tblStandard3students  
tblCandidateinfo 

tblStandard1students，tblStandard2students和tblStandard3students TBL包含有關錄取標準1,2名學生和3

tblStandars1students

Candid admitted 
    1  Y 
    2  N 
    3  Y 


tblCandidateinfo 

Candid gender Division 
    1  M  1 
    2  F  2 

等信息.. 。

現在我想要桌子這樣

Gender Students(Standard1) Students(Standard2) Students(Standard3) 
------------------------------------------------------------------------ 
Male   10     20      30  
Female   10     30      40 

我試過，但這個並沒有給我的錯誤：

SELECT case when Gender='M' then 'Male' 
      when Gender='F' then 'Female' 
     END AS Gender, 

(SELECT count(*) 
FROM tblStandard1students A 
where A.Candid=B.Candid 
) AS Students(Standard1), 

(SELECT count(*) 
FROM tblStandard2students A 
    where A.Candid=B.Candid 
) AS Students(Standard2), 

(SELECT count(*) 
FROM tblStandard3students A 
    where A.Candid=B.Candid 
) AS Students(Standard3) 


FROM tblCandidateinfo B 
group by Gender 

Answer 1

SQLFiddle demo

select 
case when Gender='M' then 'Male' 
      when Gender='F' then 'Female' 
     END AS Gender, 
sum(T.std1) as [Students(Standard1)], 
sum(T.std2) as [Students(Standard2)], 
sum(T.std3) as [Students(Standard3)] 
from 
tblCandidateinfo as C 

JOIN 
(
select Candid, 1 as std1, 0 as std2, 0 as std3 
from tblStandars1students 
union all 
select Candid, 0 as std1, 1 as std2, 0 as std3 
from tblStandars2students 
union all 
select Candid, 0 as std1, 0 as std2, 1 as std3 
from tblStandars3students 
) as T on (C.Candid=T.Candid) 

GROUP BY GENDER 

Answer 2

在這種情況下，你也可以使用PIVOT操作

SELECT CASE WHEN Gender='M' then 'Male' 
      WHEN Gender='F' then 'Female' 
     END AS Gender, [Students(Standard1)], [Students(Standard2)], [Students(Standard3)] 
FROM (
     SELECT (SELECT gender FROM tblCandidateinfo i WHERE x.Candid = i.Candid) AS gender, List 
     FROM (
      SELECT Candid, 'Students(Standard1)' AS List 
      FROM dbo.tblStandard1students 
      UNION ALL 
      SELECT Candid, 'Students(Standard2)' 
      FROM dbo.tblStandard2students 
      UNION ALL 
      SELECT Candid, 'Students(Standard3)' 
      FROM dbo.tblStandard3students 
      ) x 
    ) x2 
PIVOT 
(
    COUNT(List) FOR List IN ([Students(Standard1)], [Students(Standard2)], [Students(Standard3)]) 
) p 

演示SQLFiddle

Answer 3

此查詢語法適用於Oracle。基本上，我使用了正確的外部連接。

select case when Gender='M' then 'Male' 
      when Gender='F' then 'Female' END AS Gender, 
     count(A.candid) AS "Students(Standard1)", 
     сount(A1.candid) AS "Students(Standard2)", 
     сount(A2.candid) AS "Students(Standard3)" 
from tblStandard1students A, 
    tblStandard2students A1, 
    tblStandard3students A2, 
    tblCandidateinfo B 
where A.candid(+)=B.candid and A1.candid(+)=B.candid and A2.candid(+)=B.candid 
group by gender