1321_Restaurant_Growth.sql

SELECT visited_on, 
    SUM(SUM(amount)) OVER (
        ORDER BY visited_on 
        ROWS BETWEEN 6 PRECEDING AND CURRENT ROW
    ) AS amount,
    CAST(
        SUM(SUM(amount)) OVER (
            ORDER BY visited_on 
            ROWS BETWEEN 6 PRECEDING AND CURRENT ROW
        )/7.0
        AS  DECIMAL(10,2)
    )  AS average_amount
FROM Customer
GROUP BY visited_on
ORDER BY visited_on
OFFSET 6 ROWS;