Вземете MAX от GROUP BY

ВНИМАНИЕ:заявката няма да обработва дублиращи се записи с максимален COUNT

SELECT  commodity,  COUNT(commodity) `count` 
FROM    orders 
GROUP   BY commodity
ORDER   BY `count` DESC 
LIMIT   1

Но това ще бъде,

SELECT  commodity,  COUNT(commodity) `count` 
FROM    orders 
GROUP   BY commodity
HAVING  COUNT(commodity) =
(
    SELECT MAX(`COUNT`) 
    FROM
    (
        SELECT  COUNT(commodity) `count` 
        FROM    orders 
        GROUP   BY commodity
    )   s
)