Continents and Currencies

SELECT rc.[ContinentCode], rc.[CurrencyCode], rc.[CurrencyUsage]
FROM (
    SELECT c.[ContinentCode],
           c.[CurrencyCode],
           COUNT(c.[CurrencyCode]) AS [CurrencyUsage],
           DENSE_RANK() OVER (PARTITION BY c.[ContinentCode] ORDER BY COUNT(c.[CurrencyCode]) DESC) AS [Rank]
    FROM [Countries] c
    GROUP BY c.[ContinentCode], c.[CurrencyCode]) rc
WHERE rc.[Rank] = 1 AND rc.[CurrencyUsage] > 1