LeetCode MySQL 1435. 制作会话柱状图

+---------------------+---------+
| Column Name         | Type    |
+---------------------+---------+
| session_id          | int     |
| duration            | int     |
+---------------------+---------+
session_id 是该表主键
duration 是用户访问应用的时间, 以秒为单位

Sessions 表：
+-------------+---------------+
| session_id  | duration      |
+-------------+---------------+
| 1           | 30            |
| 2           | 199           |
| 3           | 299           |
| 4           | 580           |
| 5           | 1000          |
+-------------+---------------+

Result 表：
+--------------+--------------+
| bin          | total        |
+--------------+--------------+
| [0-5>        | 3            |
| [5-10>       | 1            |
| [10-15>      | 0            |
| 15 or more   | 1            |
+--------------+--------------+

对于 session_id 1，2 和 3 ，它们的访问时间大于等于 0 分钟且小于 5 分钟。
对于 session_id 4，它的访问时间大于等于 5 分钟且小于 10 分钟。
没有会话的访问时间大于等于 10 分钟且小于 15 分钟。
对于 session_id 5, 它的访问时间大于等于 15 分钟。

# Write your MySQL query statement below
select 
    case when duration < 300 then '[0-5>'
         when duration < 600 then '[5-10>'
         when duration < 900 then '[10-15>'
         else '15 or more'
    end
    as bin,
    ifnull(count(*),0) total 
from Sessions
group by bin

# Write your MySQL query statement below
select t2.bin, ifnull(count(t1.bin),0) total from
(
    select
        case when duration < 300 then '[0-5>'
            when duration < 600 then '[5-10>'
            when duration < 900 then '[10-15>'
            else '15 or more'
        end
        as bin        
    from Sessions
) t1
right join 
(
    select '[0-5>' as bin union
    select '[5-10>' as bin union
    select '[10-15>' as bin union
    select '15 or more' as bin
) t2
on t2.bin = t1.bin
group by t2.bin