如何構造tsql查詢以處理多個子表

Question

我需要編寫SQL Server 2005查詢來處理連接多個子表的幫助。這是我的情景：

表：

客戶

• Customer_PK

訂單

• Order_PK
• OrdersTypeA_FK
• OrdersTypeB_FK
• OrdersTypeC_FK
• Customer_FK

OrdersTypeA

• OrdersTypeA_PK
• Shipper_FK

OrdersTypeB

• OrdersTypeB_PK
• Shipper_FK

OrdersTypeC

• OrdersTypeC_PK
• Shipper_FK

託運人

• Shipper_PK
• ShipperAddress_FK

ShipperAddress

• ShipperAddress_PK
• ShipperState

的Orders表，看起來像以下數據：

Order_PK OrdersTypeA_FK OrdersTypeB_FK OrdersTypeC_FK Customer_FK 
-------- -------------- -------------- -------------- ----------- 
1   1     null    null    1 
2   null    1     null    2 
3   null    null    1     3 

我的問題是，我需要通過從三個OrdersType表中的一個查找Shipper_FK來檢索ShipperAddress。 Orders表每行只有一個OrdersType FK。我需要從OrdersType表中檢索的唯一東西是Shipper_FK，這樣我可以加入ShipperAddress表。

那麼連接看起來如何？

select 
ShipperAddress.ShipperState 
from Customers 
left join Orders on Orders.Customer_FK = Customers.Customer_PK 

???????? 

left join Shippers on Shipper_PK = ??????.Shipper_FK 
left join ShipperAddress on ShipperAddress.ShipperAddress_PK = Shippers.ShipperAddress_FK 

我不能有一個單獨的連接到ShipperAddress每個OrdersType表。這是在OrdersType級別有更多表的問題的較小示例。 Shipper_FK在每個OrdersType表中都是相同的。無論來自何處的OrdersType表繼續加入聲明，我都需要獲取Shipper_FK。如何做到這一點？

Answer 1

這將是有趣的閱讀，優化和維護......

SELECT sa.ShipperState --, other columns surely 
FROM dbo.Customers AS c 
LEFT OUTER JOIN dbo.Orders AS o 
ON o.Customer_FK = c.Customer_PK 
LEFT OUTER JOIN dbo.OrdersTypeA AS oa 
    ON oa.OrdersTypeA_PK = o.OrdersTypeA_FK 
LEFT OUTER JOIN dbo.OrdersTypeB AS ob 
    ON ob.OrdersTypeB_PK = o.OrdersTypeB_FK 
LEFT OUTER JOIN dbo.OrdersTypeC AS oc 
    ON oc.OrdersTypeC_PK = o.OrdersTypeC_FK 
LEFT OUTER JOIN dbo.Shippers AS s 
    ON s.Shipper_PK = COALESCE(oa.Shipper_FK, ob.Shipper_FK, oc.Shipper_FK) 
LEFT OUTER JOIN dbo.ShipperAddress AS sa 
    ON s.ShipperAddress_FK = sa.ShipperAddress_PK;