题目
Trips 表中存所有出租车的行程信息。每段行程有唯一键 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。
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)
+------------+-------------------+
| Day | Cancellation Rate |
+------------+-------------------+
| 2013-10-01 | 0.33 |
| 2013-10-02 | 0.00 |
| 2013-10-03 | 0.50 |
+------------+-------------------+
致谢:
非常感谢 @cak1erlizhou 详细的提供了这道题和相应的测试用例。
生成数据
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'));
TRUNCATE TABLE Trips;
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');
TRUNCATE TABLE Users;
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');
审题
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)
首先要选出非禁止用户生成的订单 再统计数量 总数很好确定
然后看被司机或乘客取消的数量 ‘completed’, ‘cancelled_by_driver’, ‘cancelled_by_client’ 有这三种情况， 因此完成记为1否则即为0即可。
解答
选出非禁止用户生成的订单
开始是这样写的先排除被禁止乘客的订单 其实没必要 因为Role为client的 Users_Id 一定在Client_Id中
SELECT *
FROM Trips AS T
JOIN Users AS U
ON T.`Client_Id` = U.`Users_Id`
WHERE U.`Role` = 'client' and U.Banned = No
这样生成即可
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')
然后根据Status统计数量
SELECT T.`Request_at`, COUNT(T.`Status`) AS all_count, SUM(IF(T.`Status` = 'completed', 0, 1)) AS uncom_count
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')
GROUP BY t.`Request_at`;
注意题目要求需要限制时间范围
SELECT T.request_at AS `Day`,
ROUND(
SUM(
IF(T.STATUS = 'completed',0,1)
)
/
COUNT(T.STATUS),
2
) AS `Cancellation Rate`
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')
WHERE T.request_at BETWEEN '2013-10-01' AND '2013-10-03'
GROUP BY T.request_at
别的方法都复杂了吧
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