對於子查詢分組中的彙總列SQL返回零

Question

我有兩個子查詢，其中一個返回一組數據併合計分組中的一列，另一個執行相同的操作，但條件是批准日期不是't null。二是再加入和選擇得到這樣的結果：

ID - Requested - Approved

如果我現在運行它，它會返回像1 - 2 - NULL，因爲記錄我m測試與未批准。在這種情況下，我希望「Approved」列顯示0而不是「NULL」。我足夠新，複雜的查詢，我不知道如何做到這一點，但我確信這是可能的。

順便說一句，這是與MS SQL服務器，所以T-SQL之類的很好，如果它更容易。

這裏的查詢，因爲它現在是：

select sr.ItemID, Requested, Approved from 

(select sri.ItemID, Requested = sum(sri.Quantity) from SupplyRequestItem as sri inner join 
SupplyRequest as sr on sr.ID = sri.RequestID 
group by sri.ItemID) as sr left outer join 

(select sri.ItemID, Approved = sum(sri.Quantity) from SupplyRequestItem as sri inner join 
SupplyRequest as sr on sr.ID = sri.RequestID 
where sr.ApprovedDate is not null 
group by sri.ItemID) as asr on sr.ItemID = asr.ItemID 

Answer 1

可以使用條件聚集，做一個簡單的方法。根據您的需要更改case表達式。

select sri.ItemID, 
Requested = sum(case when sr.ApprovedDate is null then sri.Quantity else 0 end), 
Approved = sum(case when sr.ApprovedDate is not null then sri.Quantity else 0 end) 
from SupplyRequestItem as sri 
inner join SupplyRequest as sr on sr.ID = sri.RequestID 
group by sri.ItemID