Question

Can anybody help me with this query ?

I have 3 tables : orders, customers and products.

I need to have a list of the number of orders for each customer + for each product.
Like this:

Customer A    Product X     4
Customer A    Product Y     0
Customer A    Product Z     0
Customer B    Product X     2
Customer B    Product Y     0
Customer B    Product Z     1
Customer C    Product X     0
Customer C    Product Y     0
Customer C    Product Z     8

I tried a query like this :

SELECT c.Name, p.Name, COUNT(o.OrderID)
FROM orders AS o
RIGHT JOIN customers AS c ON c.CustomerID=o.CustomerID
RIGHT JOIN products AS p ON p.ProductID=o.ProductID
GROUP BY c.Name, p.Name

but I can’t get it to work !
It only displays the combinations where the counter>0 (where there are records in ‘orders’). But with only 1 join it DOES work, and then it DOES correctly display the records with a counter of 0. (In this example there are no products Y sold, but I do want to see Y in the list of combinations)

Any ideas?

Answer 1

Use a cross join. This is Oracle SQL, so not sure if it’ll work for mysql.

select c.Name, p.Name, count(o.orderid)
from customers c cross join products p
left join orders o on c.customerid=o.CustomerID and p.ProductID=o.ProductID
GROUP BY c.Name, p.Name
order by c.name, p.name