mysql update select 从查询结果中更新数据

UPDATE user_online_month_atu a
INNER JOIN (
SELECT
user_id,
sum(c.online_times) as totalSum,
LEFT(c.log_date,length(c.log_date) - 2) as date
FROM
user_online_time_atu c
GROUP BY
c.user_id ,date
) b ON a.user_id = b.user_id AND a.`month`=b.date
SET a.online_time = b.totalSum

原文地址：https://www.cnblogs.com/deepalley/p/11018918.html