SELECT `number` , COUNT( * )
FROM (
SELECT `number1` AS `number`
FROM `table`
UNION ALL SELECT `number2` AS `number`
FROM `table`
UNION ALL SELECT `number3` AS `number`
FROM `table`
UNION ALL SELECT `number4` AS `number`
FROM `table`
UNION ALL SELECT `number5` AS `number`
FROM `table` LIMIT 100
) AS `temp`
GROUP BY `number`
ORDER BY COUNT( * ) DESC
Есть:
Flag of Albania.svg Албания — Республика Албания
Flag of Belarus.svg Белоруссия — Республика Беларусь
Должно получиться:
Албания, Белоруссия