Question

This is my ERD for my database contains three tables:

I want to retrieve data from this tables, So I wrote following Query:

SELECT [SrvcDate], [Order].OrderID, [EmployeeID], [CustID], [ComputerID]
FROM [Order], [OtherService], [ServiceOrder]
WHERE [Order].[OrderID]=[OtherService].[OrderID]
OR [Order].OrderID= [ServiceOrder].OrderID

But this query only returns data if both [OtherService] and [ServiceOrder] tables contains any data. but If there is no data in one of the tables, query doesn’t retrieve data even if the other tables contain some data.

For example, say I have couple of records in [OtherService] table but I don’t have any data in [ServiceOrder] table, this query should bring all the data that are in [OtherService] table right? but it does not retrieve any record even though I have record in [OtherService] tables. Why is that?

Answer 1

Stop using old-style joins and please use the schema prefix. Your query should be:

SELECT o.[SrvcDate], o.OrderID, o.[EmployeeID], o.[CustID], o.[ComputerID]
--, I assume some columns from OtherService / ServiceOrder
FROM dbo.[Order] AS o
LEFT OUTER JOIN dbo.[OtherService] AS os
ON os.OrderID = o.OrderID
LEFT OUTER JOIN dbo.[ServiceOrder] AS so
ON so.OrderID = o.OrderID;

If you want there to be at least one row in either OtherService or ServiceOrder then add:

WHERE COALESCE(os.OrderID, so.OrderID) IS NOT NULL