Continents and Currencies - with CTE ( T-SQL )

-- 15.Continents and Currencies From Subqueries and Joins
WITH CTE AS
(
  SELECT Countries.ContinentCode, Countries.CurrencyCode, COUNT(Countries.CurrencyCode) AS CurrencyUsage,
  DENSE_RANK() OVER(PARTITION BY Countries.ContinentCode ORDER BY COUNT(Countries.CurrencyCode) DESC) AS RN
  FROM Countries
  GROUP BY Countries.CurrencyCode, Countries.ContinentCode
)
SELECT ContinentCode, CurrencyCode, CurrencyUsage
FROM CTE
WHERE RN = 1 AND CTE.CurrencyUsage != 1
ORDER BY CTE.ContinentCode