关于我的查询的快速问题（AVG，OVER，GROUP BY问题）

Question

我尝试使用AVG和OVER来平均获得7天，但被卡住了。 我不知道这是怎么回事。

您能帮我发现问题吗？

SELECT
    dt
    , SUM(purchase_amount) as total_amount
    , AVG(SUM(purchase_amount))
    OVER(ORDER BY dt 
        ROWS BETWEEN 6 PRECEDING AND CURRENT ROW) as seven_day_avg
FROM purchase_log
GROUP BY dt
ORDER BY dt

ERROR:
Error Code: 1064. You have an error in your SQL syntax; 
check the manual that corresponds to your MySQL server version for the right syntax to use near 
'(ORDER BY dt row between 6 preceding and current row) as seven_day_avg ' at line 5