MySQL 按日累加求销量 按月累加求销量

Select
    a.id,
    a.product,
    a.sale_date,
    a.num ,
    (
        Select
            sum(num)
        FROM
            t_sale_stats b
        Where
            b.id <= a.id
        AND b.product = '产品名称'
        AND b.sale_date >= '2015-03-01'
        AND b.sale_date <= '2015-03-05'
    ) cum_num
FROM
    t_sale_stats a
Where
    a.sale_date >= '2015-03-01'
AND a.sale_date <= '2015-03-05'
AND a.product = '产品名称'
ORDER BY