MySQL行程和用户

Posted 2021-09-01 willem_chen

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mysql行程和用户

SQL架构
题目描述
题解

SQL架构

Create table If Not Exists Trips (Id int, Client_Id int, Driver_Id int, City_Id int, Status ENUM('completed', 'cancelled_by_driver', 'cancelled_by_client'), Request_at varchar(50));
Create table If Not Exists Users (Users_Id int, Banned varchar(50), Role ENUM('client', 'driver', 'partner'));

insert into Trips (Id, Client_Id, Driver_Id, City_Id, Status, Request_at) values ('1', '1', '10', '1', 'completed', '2013-10-01');
insert into Trips (Id, Client_Id, Driver_Id, City_Id, Status, Request_at) values ('2', '2', '11', '1', 'cancelled_by_driver', '2013-10-01');
insert into Trips (Id, Client_Id, Driver_Id, City_Id, Status, Request_at) values ('3', '3', '12', '6', 'completed', '2013-10-01');
insert into Trips (Id, Client_Id, Driver_Id, City_Id, Status, Request_at) values ('4', '4', '13', '6', 'cancelled_by_client', '2013-10-01');
insert into Trips (Id, Client_Id, Driver_Id, City_Id, Status, Request_at) values ('5', '1', '10', '1', 'completed', '2013-10-02');
insert into Trips (Id, Client_Id, Driver_Id, City_Id, Status, Request_at) values ('6', '2', '11', '6', 'completed', '2013-10-02');
insert into Trips (Id, Client_Id, Driver_Id, City_Id, Status, Request_at) values ('7', '3', '12', '6', 'completed', '2013-10-02');
insert into Trips (Id, Client_Id, Driver_Id, City_Id, Status, Request_at) values ('8', '2', '12', '12', 'completed', '2013-10-03');
insert into Trips (Id, Client_Id, Driver_Id, City_Id, Status, Request_at) values ('9', '3', '10', '12', 'completed', '2013-10-03');
insert into Trips (Id, Client_Id, Driver_Id, City_Id, Status, Request_at) values ('10', '4', '13', '12', 'cancelled_by_driver', '2013-10-03');

insert into Users (Users_Id, Banned, Role) values ('1', 'No', 'client');
insert into Users (Users_Id, Banned, Role) values ('2', 'Yes', 'client');
insert into Users (Users_Id, Banned, Role) values ('3', 'No', 'client');
insert into Users (Users_Id, Banned, Role) values ('4', 'No', 'client');
insert into Users (Users_Id, Banned, Role) values ('10', 'No', 'driver');
insert into Users (Users_Id, Banned, Role) values ('11', 'No', 'driver');
insert into Users (Users_Id, Banned, Role) values ('12', 'No', 'driver');
insert into Users (Users_Id, Banned, Role) values ('13', 'No', 'driver');

题目描述

表：Trips

+-------------+----------+
| Column Name | Type     |
+-------------+----------+
| Id          | int      |
| Client_Id   | int      |
| Driver_Id   | int      |
| City_Id     | int      |
| Status      | enum     |
| Request_at  | date     |     
+-------------+----------+

Id 是这张表的主键。

这张表中存所有出租车的行程信息。每段行程有唯一 Id ，其中 Client_Id 和 Driver_Id 是 Users 表中 Users_Id 的外键。

Status 是一个表示行程状态的枚举类型，枚举成员为(‘completed’, ‘cancelled_by_driver’, ‘cancelled_by_client’) 。

表：Users

+-------------+----------+
| Column Name | Type     |
+-------------+----------+
| Users_Id    | int      |
| Banned      | enum     |
| Role        | enum     |
+-------------+----------+

Users_Id 是这张表的主键。

这张表中存所有用户，每个用户都有一个唯一的 Users_Id ，Role 是一个表示用户身份的枚举类型，枚举成员为 (‘client’, ‘driver’, ‘partner’) 。

Banned 是一个表示用户是否被禁止的枚举类型，枚举成员为 (‘Yes’, ‘No’) 。

写一段 SQL 语句查出 “2013-10-01” 至 “2013-10-03” 期间非禁止用户（乘客和司机都必须未被禁止）的取消率。非禁止用户即 Banned 为 No 的用户，禁止用户即 Banned 为 Yes 的用户。

取消率的计算方式如下：(被司机或乘客取消的非禁止用户生成的订单数量) / (非禁止用户生成的订单总数)。

返回结果表中的数据可以按任意顺序组织。其中取消率 Cancellation Rate 需要四舍五入保留两位小数。

查询结果格式如下例所示：

Trips 表：
+----+-----------+-----------+---------+---------------------+------------+
| 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：
+----------+--------+--------+
| 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 |
+----------+--------+--------+

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

2013-10-01：
  - 共有 4 条请求，其中 2 条取消。
  - 然而，Id=2 的请求是由禁止用户（User_Id=2）发出的，所以计算时应当忽略它。
  - 因此，总共有 3 条非禁止请求参与计算，其中 1 条取消。
  - 取消率为 (1 / 3) = 0.33
2013-10-02：
  - 共有 3 条请求，其中 0 条取消。
  - 然而，Id=6 的请求是由禁止用户发出的，所以计算时应当忽略它。
  - 因此，总共有 2 条非禁止请求参与计算，其中 0 条取消。
  - 取消率为 (0 / 2) = 0.00
2013-10-03：
  - 共有 3 条请求，其中 1 条取消。
  - 然而，Id=8 的请求是由禁止用户发出的，所以计算时应当忽略它。
  - 因此，总共有 2 条非禁止请求参与计算，其中 1 条取消。
  - 取消率为 (1 / 2) = 0.50

题解

统计每天非禁止用户的取消率，需要知道非禁止用户有哪些，总行程数，取消的行程数。

解法一

首先确定被禁止用户的行程记录，再剔除这些行程记录。

行程表中，字段 client_id 和 driver_id，都与用户表中的 users_id 关联。因此只要 client_id 和 driver_id 中有一个被禁止了，此条行程记录要被剔除。

先说一种错误的找出没被禁止用户行程记录的方法。此方法很有迷惑性。

思路：

if (client_id = users_id 或 driver_id = users_id) 且 users_id没有被禁止
{
    此条记录没被禁止。
}

SELECT *
FROM Trips AS T JOIN Users AS U 
ON (T.client_id = U.users_id  OR T.driver_id = U.users_id )  AND U.banned ='No';

乍一看，思路是对。其实是错误的。因为，我们不知觉得肯定了一个假设—— client_id 与 driver_id 是相同的。只有当两者相同时，才能用此条件排除被禁止用户的行程记录。

错误的结果：

+------+-----------+-----------+---------+---------------------+------------+----------+--------+--------+
| Id   | Client_Id | Driver_Id | City_Id | Status              | Request_at | Users_Id | Banned | Role   |
+------+-----------+-----------+---------+---------------------+------------+----------+--------+--------+
|    1 |         1 |        10 |       1 | completed           | 2013-10-01 |        1 | No     | client |
|    1 |         1 |        10 |       1 | completed           | 2013-10-01 |       10 | No     | driver |
|    2 |         2 |        11 |       1 | cancelled_by_driver | 2013-10-01 |       11 | No     | driver |
|    3 |         3 |        12 |       6 | completed           | 2013-10-01 |        3 | No     | client |
|    3 |         3 |        12 |       6 | completed           | 2013-10-01 |       12 | No     | driver |
|    4 |         4 |        13 |       6 | cancelled_by_client | 2013-10-01 |        4 | No     | client |
|    4 |         4 |        13 |       6 | cancelled_by_client | 2013-10-01 |       13 | No     | driver |
|    5 |         1 |        10 |       1 | completed           | 2013-10-02 |        1 | No     | client |
|    5 |         1 |        10 |       1 | completed           | 2013-10-02 |       10 | No     | driver |
|    6 |         2 |        11 |       6 | completed           | 2013-10-02 |       11 | No     | driver |
|    7 |         3 |        12 |       6 | completed           | 2013-10-02 |        3 | No     | client |
|    7 |         3 |        12 |       6 | completed           | 2013-10-02 |       12 | No     | driver |
|    8 |         2 |        12 |      12 | completed           | 2013-10-03 |       12 | No     | driver |
|    9 |         3 |        10 |      12 | completed           | 2013-10-03 |        3 | No     | client |
|    9 |         3 |        10 |      12 | completed           | 2013-10-03 |       10 | No     | driver |
|   10 |         4 |        13 |      12 | cancelled_by_driver | 2013-10-03 |        4 | No     | client |
|   10 |         4 |        13 |      12 | cancelled_by_driver | 2013-10-03 |       13 | No     | driver |
+------+-----------+-----------+---------+---------------------+------------+----------+--------+--------+
17 rows in set (0.00 sec)

结果中，被禁止的 users_id = 2，其行程记录没被剔除掉。

明显， client_id 与 driver_id 不一定相同。

正确的做法是对 client_id 和 driver_id 各自关联的 users_id，同时检测是否被禁止。

if (client_id = users_id_1 且 users_id_1没被禁止 并且 client_id = users_id_2 且 users_id_2没被禁止){
    此条记录没被禁止。
}

SELECT *
FROM Trips AS T
JOIN Users AS U1 ON (T.client_id = U1.users_id AND U1.banned ='No')
JOIN Users AS U2 ON (T.driver_id = U2.users_id AND U2.banned ='No');

+------+-----------+-----------+---------+---------------------+------------+----------+--------+--------+----------+--------+--------+
| Id   | Client_Id | Driver_Id | City_Id | Status              | Request_at | Users_Id | Banned | Role   | Users_Id | Banned | Role   |
+------+-----------+-----------+---------+---------------------+------------+----------+--------+--------+----------+--------+--------+
|    1 |         1 |        10 |       1 | completed           | 2013-10-01 |        1 | No     | client |       10 | No     | driver |
|    3 |         3 |        12 |       6 | completed           | 2013-10-01 |        3 | No     | client |       12 | No     | driver |
|    4 |         4 |        13 |       6 | cancelled_by_client | 2013-10-01 |        4 | No     | client |       13 | No     | driver |
|    5 |         1 |        10 |       1 | completed           | 2013-10-02 |        1 | No     | client |       10 | No     | driver |
|    7 |         3 |        12 |       6 | completed           | 2013-10-02 |        3 | No     | client |       12 | No     | driver |
|    9 |         3 |        10 |      12 | completed           | 2013-10-03 |        3 | No     | client LeetCode（数据库）- 行程和用户
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