计算每天的增量，增率

SELECT
DATE_FORMAT(add_time, "%Y-%m-%d") order_date,
SUM(sold) AS today_c,
SUM(sold) - last_c AS change_with_last
FROM
orders
LEFT JOIN (
SELECT
DATE_FORMAT(t.add_time, "%Y-%m-%d") AS last_date,
SUM(t.sold) AS last_c
FROM
orders t
GROUP BY
DATE_FORMAT(t.add_time, "%Y-%m-%d")
) last ON (
DATE_FORMAT(add_time, "%Y-%m-%d") = DATE_ADD(
last.last_date,
INTERVAL 1 DAY
)
)
GROUP BY

DATE_FORMAT(add_time);