MySQL 任務四打卡 DW

專案十：

行程和使用者（難度：困難） trips 表中存所有計程車的行程資訊。每段行程有唯一鍵 id，client_id 和 driver_id 是 users 表中 users_id 的外來鍵。status 是列舉型別，列舉成員為 (『completed』, 『cancelled_by_driver』, 『cancelled_by_client』)。

| 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 表存所有使用者。每個使用者有唯一鍵 users_id。banned 表示這個使用者是否被禁止，role 則是乙個表示（『client』, 『driver』, 『partner』）的列舉型別。

| 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 |

寫一段 sql 語句查出 **2023年10月1日 **至 **2023年10月3日 **期間非禁止使用者的取消率。基於上表，你的 sql 語句應返回如下結果，取消率（cancellation rate）保留兩位小數。

| day | cancellation rate |

| 2013-10-01 | 0.33 |

| 2013-10-02 | 0.00 |

| 2013-10-03 | 0.50 |

create table users (
users_id int not null primary key,
banned varchar(20) default 'no',
role varchar(20) check (role in ('client','driver','partner'))
);create table trips (
id int not null primary key,
client_id int not null references users(users_id),
driver_id int not null references users(users_id),
city_id int,
status varchar(50) check (status in ('completed','cancelled_by_driver','cancelled_by_client')),
request_at date
);insert into users values 
(1,'no','client'),
(2,'yes','client'),
(3,'no','client'),
(4,'no','client'),
(10,'no','driver'),
(11,'no','driver'),
(12,'no','driver'),
(13,'no','driver');
insert into trips values 
(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');
select request_at as day, round(count(status != 'completed' or null)/count(*),2) as "cancellation rate"
from trips, users
where trips.client_id = users.users_id
and banned="no" and request_at between "2013-10-1" and "2013-10-3"
group by request_at;

專案十一：

各部門前3高工資的員工（難度：中等）將專案7中的employee表清空，重新插入以下資料（其實是多插入5,6兩行）：

| 1 | joe | 70000 | 1 |

| 2 | henry | 80000 | 2 |

| 3 | sam | 60000 | 2 |

| 4 | max | 90000 | 1 |

| 5 | janet | 69000 | 1 |

| 6 | randy | 85000 | 1 |

編寫乙個 sql 查詢，找出每個部門工資前三高的員工。例如，根據上述給定的**，查詢結果應返回：

| department | employee | salary |

| it | max | 90000 |

| it | randy | 85000 |

| it | joe | 70000 |

| sales | henry | 80000 |

| sales | sam | 60000 |

此外，請考慮實現各部門前n高工資的員工功能。

create table employee(
id int not null primary key,
name varchar(255) not null,
salary int not null,
departmentid int not null
);create table department(
id int not null primary key,
name varchar(255) not null
);insert into employee values
(1,"joe",70000,1),
(2,"henry",80000,2),
(3,"sam",60000,2),
(4,"max",90000,1),
(5,"janet",69000,1),
(6,"randy",85000,1);
insert into department values
('1','it'),
('2','sales');

專案十二

分數排名 - （難度：中等）依然是昨天的分數表，實現排名功能，但是排名是非連續的，如下：

| score | rank |

| 4.00 | 1 |

| 3.85 | 3 |

| 3.65 | 4 |

| 3.50 | 6 |

select score,(select count(score)+1
from score
where score>s.score) as r
from score as s
order by score desc;

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