MySQL - 按唯一登录天数范围内的用户数量和按部门分组

Question

我正在进行一项查询,它将计算每个用户的唯一登录天数,将它们放入一个桶中(1-2,3-4个登录日等),并返回每个用户的数量.按部门划分.如果不太清楚我会道歉,希望下面的例子有助于说明我的问题.

我有这样一张桌子:

+-------------+-----------+------------+-----------------+
|    time     | user_name |    dept    |      event      |
+-------------+-----------+------------+-----------------+
| 2016-01-04  | Joe       | finance    | logged in       |
| 2016-01-04  | Jeff      | marketing  | logged in       |
| 2016-01-04  | Jeff      | marketing  | project created |
| 2016-01-04  | Bob       | finance    | logged in       |
| 2016-01-04  | Mark      | accounting | logged in       |
| 2016-01-05  | Bob       | finance    | logged in       |
| 2016-01-08  | Bob       | finance    | logged in       |
| 2016-01-09  | Jeff      | marketing  | logged in       |
| 2016-01-10  | Jeff      | marketing  | logged in       |
| 2016-01-11  | Nate      | accounting | logged in       |
| 2016-01-11  | Nate      | accounting | project created |
+-------------+-----------+------------+-----------------+

我想返回一个这样的表:

+------------------+-----------------+------------+
| number of logins | number of users |    dept    |
+------------------+-----------------+------------+
| 1-2              |               1 | finance    |
| 3-4              |               1 | finance    |
| 5+               |               0 | finance    |
| 1-2              |               0 | marketing  |
| 3-4              |               1 | marketing  |
| 5+               |               0 | marketing  |
| 1-2              |               2 | accounting |
| 3-4              |               0 | accounting |
| 5+               |               0 | accounting |
+------------------+-----------------+------------+ 

截至目前,我的查询如下:

select 
(case when count(distinct(`time`)) between 1 and 2 then '1-2' 
      when count(distinct(`time`)) between 3 and 4 then '3-4'
      else '5+'
        end) as buckets, dept, user_name
    from change_log where event in ('logged in')  
    group by dept, user_name

然而,这会返回一个如下表格,这是我能够达到我想要的最接近的表格,但我不知道如何将其推广到只有桶和部门.

+---------+------------+-----------+
| buckets |    dept    | user_name |
+---------+------------+-----------+
| 1-2     | accounting | Mark      |
| 1-2     | accounting | Nate      |
| 3-4     | finance    | Bob       |
| 1-2     | finance    | Joe       |
| 3-4     | marketing  | Jeff      |
+---------+------------+-----------+

Answer 1

像这样的东西吗？

select buckets, dept, count(user_name) no_of_u from 
(select 
(case when count(distinct(`time`)) between 1 and 2 then '1-2' 
      when count(distinct(`time`)) between 3 and 4 then '3-4'
      else '5+'
        end) as buckets, dept, user_name
    from change_log where event in ('logged in')  
    group by dept, user_name)
group by buckets, dept