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Providing detailed information and counting objects
Calculating metrics for multiple business objects
6. Total order value
Understanding the difference between various count metrics


Good job! In sales reports, we frequently need to calculate the total sum paid for an order. Let's take a look at how we can do that:

  SUM(UnitPrice * Quantity) AS TotalPrice
FROM Orders O
JOIN OrderItems OI
  ON O.OrderID = OI.OrderID
WHERE O.OrderID = 10250;

We want to find the total price (before discount) for the order with ID of 10250. As you can see, we use SUM(UnitPrice * Quantity). Like COUNT(), SUM() is frequently used in business reports.


The template code shows the query from the explanation. The Northwind store offers its customers discounts for some products. The discount for each item is stored in the Discount column of the OrderItem table. (For example, a 0.20 discount means that the customer pays 1 - 0.2 = 0.8 of the original price.) Your task is to add a second column named TotalPriceAfterDiscount.

Stuck? Here's a hint!

The new column should use the following formula:

UnitPrice * Quantity * (1 - Discount)