Comparing Performance

To compare the performance and observe the linear scaling, we will perform a query that will require heavy processing. The following query calculates the number of items a customer bought of his or her favorite item. We order it in an ASCENDING fashion based on the Customer ID and display the first 5.

Though at first glance it might look like a simple query, it involves reading and processing a large amount of data.

The query for the total number of items bought by a customer:

SELECT 
    c.Name, 
    c.Item, 
    COUNT(*) AS NumberOfItems
FROM 
    Customers c
JOIN 
    Purchases p ON c.CustomerID = p.CustomerID AND c.Item = p.Item
GROUP BY 
    c.Name, c.Item, c.CustomerID
ORDER BY 
    c.CustomerID ASC
LIMIT 5;