使用LEFT JOIN，聯盟和右加入以獲得期望的結果

Question

我有兩個表，即 「CProduct」 和 「DPRODUCT」。下面是例子：

CProduct：

EffectiveDate CFund 
2014-01-03  0.06 
2014-01-03  0.12 
2014-01-06  0.11 

DPRODUCT：

EffectiveDate DFund 
2014-01-03  0.06 
2014-01-06  0.12 
2014-01-08  0.09 

我想要得到的結果如下圖所示：

EffectiveDate CFund DFund 
2014-01-03  0.18 0.06 
2014-01-06  0.11 0.12 
2014-01-08  NULL 0.09 

我的查詢是：

SELECT a.EffectiveDate,a.CFund,a.DFund  
FROM (
SELECT t1.EffectiveDate,Sum(t1.CFund) as CFund ,SUM(t2.DFund) as DFund FROM CProduct t1 
LEFT JOIN DProduct t2 ON t1.EffectiveDate = t2.EffectiveDate Group By t1.EffectiveDate 
UNION 
SELECT t1.EffectiveDate,SUM(t2.CFund) as CFund ,Sum(t1.DFund) as DFund FROM DProduct t1 
LEFT JOIN CProduct t2 ON t1.EffectiveDate = t2.EffectiveDate Group By t1.EffectiveDate 
) a 

但我沒有得到預期的結果。

Answer 1

這得到您想要的結果 - 不明白爲什麼其他的應答者認爲連接和COALESCE如此重要的原因：

SELECT a.EffectiveDate, SUM(a.CFund) AS CFund, SUM(a.DFund) AS DFund 
FROM (
    SELECT c.EffectiveDate, c.CFund, NULL AS DFund 
    FROM CProduct c 
    UNION ALL 
    SELECT d.EffectiveDate, NULL AS CFund, d.DFund 
    FROM DProduct d 
) a 
GROUP BY a.EffectiveDate 
ORDER BY a.EffectiveDate 

在SQL小提琴，對SQLite的（我沒有檢查，但應罰款與Access太） ：http://sqlfiddle.com/#!7/80158/1

Answer 2

應該只是一些子查詢和一個完整的外連接。不知道爲什麼你認爲UNION是必需的（尤其是因爲消除重複行）：

SELECT 
    COALESCE(t1.EffectiveDate,t2.EffectiveDate) as EffectiveDate, 
    t1.Total, 
    t2.Total 
FROM 
    (select EffectiveDate,SUM(CFund) 
    from CProduct 
    group by EffectiveDate) as t1(EffectiveDate,Total) 
     full outer join 
    (select EffectiveDate,SUM(DFund) 
    from DProduct 
    group by EffectiveDate) as t2(EffectiveDate,Total) 
     on 
      t1.EffectiveDate = t2.EffectiveDate 

Answer 3

您使用的是相對的外與UNION爲了模仿FULL OUTER JOIN聯接。這是可以的，但並不是必需的，因爲SQL Server 2008（和2005年也是如此）具有完整的外連接。

但是，您的問題更根本。您將加入來自CProduct和DProduct的所有記錄，然後構建總和。因此，對於日期2014-01-01來說，CProduct中有兩條記錄，DProduct中有三條記錄。你的加入給你六條記錄（2×3）。然後你建立你的總和，因此考慮DProduct值兩倍和CProduct條目三倍。

說了這些之後，您不希望按每個單個DProduct記錄按日期加入每個單個CProduct記錄。你想加入每個日期的總和。即先彙總，然後加入。

select 
    coalesce(c.effectivedate, d.effectivedate) as effectivedate, 
    coalesce(c.sumfund,0) as cfund, 
    coalesce(d.sumfund,0) as dfund 
from 
    (select effectivedate, sum(cfund) as sumfund from cproduct group by effectivedate) c 
full outer join 
    (select effectivedate, sum(dfund) as sumfund from dproduct group by effectivedate) d 
on c.effectivedate = d.effectivedate; 

沒有FULL OUTER JOIN：

select 
    c.effectivedate, 
    c.sumfund as cfund, 
    d.sumfund as dfund 
from 
    (select effectivedate, sum(cfund) as sumfund from cproduct group by effectivedate) c 
left outer join 
    (select effectivedate, sum(dfund) as sumfund from dproduct group by effectivedate) d 
on c.effectivedate = d.effectivedate 
union 
select 
    d.effectivedate, 
    c.sumfund as cfund, 
    d.sumfund as dfund 
from 
    (select effectivedate, sum(cfund) as sumfund from cproduct group by effectivedate) c 
right outer join 
    (select effectivedate, sum(dfund) as sumfund from dproduct group by effectivedate) d 
on c.effectivedate = d.effectivedate; 

Answer 4

使用合併或類似的是正確的解決方案。

但是在你的情況下可以避免它，想法是在一個單獨的子查詢中獲取日期，然後通過左加入來獲得總和。

SELECT 
Date.EffectiveDate as EffectiveDate, 
t1.Total as t1, 
t2.Total as t2 
FROM 
(select distinct EffectiveDate from CProduct 
union 
select distinct EffectiveDate from DProduct 
) as Date 
left join 
(select EffectiveDate,SUM(CFund) 
from CProduct 
group by EffectiveDate) as t1(EffectiveDate,Total) 
on Date.EffectiveDate=t1.EffectiveDate 
left join 
(select EffectiveDate,SUM(DFund) 
from DProduct 
group by EffectiveDate) as t2(EffectiveDate,Total) 
    on 
     Date.EffectiveDate = t2.EffectiveDate 

Answer 5

SELECT E121.EffectiveDate，SUM（E12.Cfund）AS CFUND，AVG（e121.Dfund）AS DFUND FROM E121 LEFT JOIN E12 ON E121.EffectiveDate = E12.EffectiveDate GROUP BY E121.EffectiveDate