mysql - 枚举类型和 MySQL

Question

我有一个简单的任务，但我被困住了。我有表login_history

`login_history_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`login_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
`login_action` enum('login','logout') NOT NULL,
`user_id` int(11) unsigned NOT NULL, (this one is foreign key)

任务:编写一个查询，查找 2012 年 9 月星期三注销次数最多的用户。

正如你所看到的，我有一个 enum 类型的 login_action，我需要找到哪个用户在某个特定的日子里注销最多。这就是我到目前为止所做的，我只需要朝着正确的方向插入一点点，有人告诉我我这里错了..

SELECT fullname FROM user WHERE user_id = (
SELECT user_id FROM login_history WHERE (user_id,login_action) = (
    SELECT user_id, COUNT(login_action) FROM login_history WHERE login_action = 'logout' AND login_time = (
        SELECT login_time FROM login_history WHERE YEAR(login_time) = 2012 AND MONTH(login_time) = 9 AND DAYOFWEEK(login_time) = 3)));

Answer 1

试试这个:

select u.fullname from (select count(*) n,user_id 
from login_history where 
login_time between '2012-09-01' and '2012-10-01' and dayofweek(login_time) = 3 and login_action = 'logout'
group by user_id order by n desc limit 1) a, user u where a.user_id = u.user_id

为了获得良好的性能，请确保您在 login_time 列上有一个键。