mysql varchar类型中的数字排序问题

SELECT
	a.id AS "floor.id",
	a.floor_name AS "floor.floorName"
FROM
	res_floor a
WHERE
	a.del_flag = false
AND a.unit_id ='f088b646cf3346c48e7e6cf95bc88879'
ORDER BY
	(a.floor_name+0)