Continents and Currencies

CREATE TABLE IF NOT EXISTS `continents_currencies` AS SELECT `c`.`continent_code`,
    `c`.`currency_code`,
    COUNT(`c`.`currency_code`) AS `currency_usage` FROM
    `countries` AS `c`
GROUP BY `c`.`continent_code`,`c`.`currency_code`
HAVING `currency_usage` > 1
ORDER BY `c`.`continent_code` , `c`.`currency_code`;

SELECT
    `cc`.*
FROM
    `continents_currencies` AS `cc`
        LEFT JOIN
    `continents_currencies` AS `cc2` ON `cc`.`continent_code` = `cc2`.`continent_code`
        AND `cc`.`currency_usage` < `cc2`.`currency_usage`
WHERE
    `cc2`.`currency_usage` IS NULL;

DROP TABLE `continents_currencies`;