Question

I’ve never worked with a non-normalized database before, so I’ll try and explain my problem as best I can. So I have two tables:

The customers table holds all the customers information, and the orders table holds all the orders that they have placed. I haven’t listed all the fields in the tables, just the ones that I need. The customer number in both tables is not the primary key, but I’m inner joining on them anyway. So the problem I’m having is that I don’t know how to make a query that:

Selects all the customers with their first name, last name, and email, and also show the most recent orderdate, most recent total, and most recent ordertype. I know that I have to use a max() aggregate for the date, but that’s as far as I got. Please help a noob out.

Answer 1

You can try:

SELECT FirstName,
       LastName,
       Email,
       OrderDate,
       OrderTotal,
       OrderType

FROM Customers AS C
INNER JOIN Order AS O
  ON O.CustomerNumber = C.CustomerNumber AND
     O.OrderDate = (
                    SELECT MAX (O1.OrderDate)
                    FROM Order AS O1
                    WHERE O1.CustomerNumber = C.CustomerNumber)
                   )