15.Continents and Currencies

SELECT
    koko.*, MAX(koko.currency_usage) AS maxy
FROM
    (SELECT
        c.continent_code,
            v.currency_code,
            COUNT(c.currency_code) AS 'currency_usage'
    FROM
        countries AS c
    JOIN currencies AS v ON c.currency_code = v.currency_code
    GROUP BY c.continent_code , v.currency_code
    HAVING `currency_usage` > 1
    ORDER BY c.continent_code , v.currency_code) AS koko
GROUP BY koko.continent_code;