题解 | 获取指定客户每月的消费额

SELECT time,
total
FROM
(
SELECT t_cus,
 date_format(t_time,'%Y-%m') as time,
sum(t_amount) as total
FROM trade
JOIN
(SELECT c_id
FROM customer
WHERE c_name = 'Tom'
) c 
ON c.c_id = trade.t_cus
WHERE YEAR(t_time) = 2023
AND t_type = 1
GROUP BY t_cus,date_format(t_time,'%Y-%m')
 ## date_format函数要在group by中完整体现

)t
order by time