A. SELECT c.CustomerID, c.CustomerName, o.ShippingCountry
FROM Customer c
INNER JOIN (SELECT CustomerID, ShippingCountry,
RANK() OVER (PARTITION BY CustomerID
ORDER BY COUNT(OrderAmount) DESC) AS Rnk
FROM Orders GROUP BY CustomerID, ShippingCountry)
AS o ON c.CustomerID = o.CustomerID WHERE o.Rnk = 1

B. SELECT c.CustomerID, c.CustomerName, o.ShippingCountry
FROM (SELECT c.CustomerID, c.CustomerName, o.ShippingCountry,
RANK()OVER (PARTITION BY CustomerID
ORDER BY COUNT(o.OrderAmount) ASC) AS Rnk
FROM Customer c
INNER JOIN Orders o ON c.CustomerID = o.CustomerID
GROUP BY c.CustomerID, c.CustomerName, o.ShippingCountry) cs
WHERE Rnk = 1

C. SELECT c.CustomerID, c.CustomerName, o.ShippingCountry
FROM Customer c
INNER JOIN (SELECT CustomerID, ShippingCountry,
RANK() OVER (PARTITION BY CustomerID
ORDER BY OrderAmount DESC) AS Rnk
FROM Orders GROUP BY CustomerID, ShippingCountry) AS o
ON c.CustomerID = o.CustomerID
WHERE o.Rnk = 1

D. SELECT c.CustomerID, c.CustomerName, o.ShippingCountry
FROM Customer c INNER JOIN (SELECT
CustomerID, ShippingCountry,COUNT(OrderAmount) DESC)
AS OrderAmount FROM Orders GROUP BY CustomerID, ShippingCountry)
AS o ON c.CustomerID = o.CustomerID ORDER BY OrderAmount DESC