Most recent record in a left join

Question

Imagine I have the following 3 tables in SqlServer:

Customer (CustomerID, FirstName, LastName)
Address (AddressID, CustomerID, Line1, City, State)
Product (P         


        

Answer 1

I don't see how you can do this without having Orders and OrderDetails tables. The Orders table would include the CustomerID ShippingDate and ShipToAddressID, and OrderDetails would have the OrderID and ProductID. You'll then need a nested query to determine the most recent order (and hence most recent address), join that to the order details to get the products ordered, then filter on the product you care about.

Answer 2

Try this:

SELECT a.State, count(c.CustomerID)
FROM Product p
INNER JOIN Customer c ON c.CustomerID = p.CustomerID
LEFT JOIN Address a ON a.CustomerID = c.CustomerID 
      AND a.AddressID = 
        (
           SELECT MAX(AddressID) 
           FROM Address z 
           WHERE z.CustomerID = a.CustomerID
        )
WHERE p.ProductID = 101
GROUP BY a.State

Answer 3

You could also try (assuming I remember my SQLServer syntax correctly):

SELECT state, count(customer_id)
FROM (
    SELECT
        p.customer_id
        , (SELECT TOP 1 State FROM Address WHERE Address.CustomerID = p.CustomerID ORDER BY Address.ID DESC) state
    FROM Product p
    WHERE p.ProductID = 101)
GROUP BY state