Leetcode | 行程和用户

[techiall]

Trips 表中存所有出租车的行程信息。每段行程有唯一健 Id，Client_Id 和 Driver_Id 是 Users 表中 Users_Id 的外键。Status 是枚举类型，枚举成员为 (‘completed’, ‘cancelled_by_driver’, ‘cancelled_by_client’)。

+----+-----------+-----------+---------+--------------------+----------+
| Id | Client_Id | Driver_Id | City_Id |        Status      |Request_at|
+----+-----------+-----------+---------+--------------------+----------+
| 1  |     1     |    10     |    1    |     completed      |2013-10-01|
| 2  |     2     |    11     |    1    | cancelled_by_driver|2013-10-01|
| 3  |     3     |    12     |    6    |     completed      |2013-10-01|
| 4  |     4     |    13     |    6    | cancelled_by_client|2013-10-01|
| 5  |     1     |    10     |    1    |     completed      |2013-10-02|
| 6  |     2     |    11     |    6    |     completed      |2013-10-02|
| 7  |     3     |    12     |    6    |     completed      |2013-10-02|
| 8  |     2     |    12     |    12   |     completed      |2013-10-03|
| 9  |     3     |    10     |    12   |     completed      |2013-10-03| 
| 10 |     4     |    13     |    12   | cancelled_by_driver|2013-10-03|
+----+-----------+-----------+---------+--------------------+----------+

Users 表存所有用户。每个用户有唯一键 Users_Id。Banned 表示这个用户是否被禁止，Role 则是一个表示（‘client’, ‘driver’, ‘partner’）的枚举类型。

+----------+--------+--------+
| Users_Id | Banned |  Role  |
+----------+--------+--------+
|    1     |   No   | client |
|    2     |   Yes  | client |
|    3     |   No   | client |
|    4     |   No   | client |
|    10    |   No   | driver |
|    11    |   No   | driver |
|    12    |   No   | driver |
|    13    |   No   | driver |
+----------+--------+--------+

写一段 SQL 语句查出 2013年10月1日 至 2013年10月3日 期间非禁止用户的取消率。基于上表，你的 SQL 语句应返回如下结果，取消率（Cancellation Rate）保留两位小数。

+------------+-------------------+
|     Day    | Cancellation Rate |
+------------+-------------------+
| 2013-10-01 |       0.33        |
| 2013-10-02 |       0.00        |
| 2013-10-03 |       0.50        |
+------------+-------------------+

mysql

解决这题得知道以下几个。

• 非禁止用户的取消率 = cancelled开头的 status / 总的个数。
• if 的用法
• sum() 的用法
  • 就是字面意思，求和。
• round() 的用法
  • ROUND(X,D) -- 表示将值 X 四舍五入为小数点后 D 位的数值，D 为小数点后小数位数。

t1.Banned = 'No' //该用户未被禁止

Request_at BETWEEN '2013-10-01' AND '2013-10-03' // 题目要求的时间范围

round(sum(if(Status like 'ca%', 1, 0)) / count(*), 2) // 对得到的值保留小数点后两位，利用 if sum 进行计数，就可以算得取消率

select Request_at DAY, 

        round(sum(if(Status like 'ca%', 1, 0)) / count(*), 2) 'Cancellation Rate'

from Trips t inner join Users t1 on t.Client_Id = t1.Users_Id

where t1.Banned = 'No' AND (Request_at BETWEEN '2013-10-01' AND '2013-10-03')

GROUP BY t.Request_at;