Question

I need help with how to write a SQL Server 2005 query to handle joining multiple subtables. Here is my scenario:

Tables:

Customers

• Customer_PK

Orders

• 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

Shippers

• Shipper_PK
• ShipperAddress_FK

ShipperAddress

• ShipperAddress_PK
• ShipperState

The Orders table has data that looks like the following:

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

My issue is that I need to have the select join statement retrieve the ShipperAddress by finding the Shipper_FK from one of the three OrdersType tables. The Orders table will only have one of the OrdersType FK per row. The only thing I need to retreive from the OrdersType table is the Shipper_FK so that I can join to the ShipperAddress table.

So how does the join look???

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

I can’t have a separate join down to ShipperAddress for each of the OrdersType tables. This is a smaller sample of an issue that has many more tables at the OrdersType level. The Shipper_FK is the same in each of the OrdersType tables. I need to get at the Shipper_FK no matter what OrdersType table it came from to continue with the join statement. How can that be done?

Answer 1

This is going to be fun to read, optimize and maintain…

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;