WITH Cte_CurrenciesByContinent (ContinentCode, CurrencyCode, CurrencyUsage) AS
(
SELECT  c.ContinentCode,
        c.CurrencyCode,
        COUNT(c.CurrencyCode) AS CurrencyUsage
FROM Continents cont
LEFT JOIN Countries c ON cont.ContinentCode = c.ContinentCode
LEFT JOIN Currencies curr ON c.CurrencyCode = curr.CurrencyCode
GROUP BY c.CurrencyCode, c.ContinentCode
)
SELECT
       ContinentCode,
       CurrencyCode,
       CurrencyUsage
FROM Cte_CurrenciesByContinent c
WHERE CurrencyUsage IN (SELECT MAX(CurrencyUsage) FROM Cte_CurrenciesByContinent c2 WHERE c.ContinentCode = c2.ContinentCode)
      AND CurrencyUsage != 1
ORDER BY ContinentCode