SELECT a.product as product_a, a.customer, b.product as product_b 
FROM Sales a INNER JOIN Sales b ON a.Customer = b.Customer
WHERE a.product < b.product

##</code><code>##

SELECT a.product as product_a, b.product as product_b, count(*) as popularity 
FROM Sales a INNER JOIN Sales b ON a.Customer = b.Customer WHERE a.product < b.product
GROUP BY a.product, b.product