Now, let's analyze our e-store's "good customers." Each business will use its own definition of a good customer that is based on their business model. In our e-store, we'll define a "good customer" as a customer whose average order value is above the general average order value for all customers. Analyzing such customers may help us understand what makes customers spend more. This, in turn, can help us decide which marketing campaigns we should focus on.

First, we need to see the average order value for each individual customer:

SELECT
  C.CustomerID,
  AVG(TotalAmount) AS AvgOrderValue
FROM Customers C
JOIN Orders O
  ON C.CustomerID = O.CustomerID
GROUP BY C.CustomerID
ORDER BY AVG(TotalAmount);

The query is quite straightforward: we join the tables Customers and Orders so that we can calculate AVG(TotalAmount) and get some additional information about the customer.