# [1321. Restaurant Growth](https://leetcode.com/problems/restaurant-growth/description/?envType=study-plan-v2&envId=top-sql-50)
這次需要我們找 每7天的營業額以及平均
DATE_SUB( INTERVAL 6 DAY)可以將前6天的資訊提取出來
再取得DATA_ADD+6開始排序

SELECT visited_on,
    (SELECT SUM(amount) FROM customer WHERE visited_on 
    BETWEEN DATE_SUB(c.visited_on, INTERVAL 6 DAY) AND c.visited_on
    ) AS amount,
    ROUND(
    (SELECT SUM(amount) / 7 FROM customer WHERE visited_on 
    BETWEEN DATE_SUB(c.visited_on, INTERVAL 6 DAY) AND c.visited_on
        ),2) AS average_amount
FROM customer c
WHERE visited_on >= (SELECT DATE_ADD(MIN(visited_on), INTERVAL 6 DAY) FROM customer)
GROUP BY visited_on;