Who is the customer who purchased the highest number of products in a single order?
highest number of products refers to MAX(COUNT(ProductID))
SELECT T1.CompanyName FROM Customers AS T1 INNER JOIN Orders AS T2 ON T1.CustomerID = T2.CustomerID INNER JOIN `Order Details` AS T3 ON T2.OrderID = T3.OrderID GROUP BY T1.CompanyName ORDER BY COUNT(T3.ProductID) DESC LIMIT 1