MySQL任务就要完成了

 任务一

 sql代码

SELECT D.Name Department,E1.Name Name,SalaryFROM employee E1INNER JOIN department DON E1.DepartmentId = D.IDWHERE (SELECT COUNT(*) FROM employee E2 WHERE E1.Salary <= E2.Salary AND E1.DepartmentId = E2.DepartmentId) <= 3

运行结果：

 任务二

sql语句：

SELECT Score,(SELECT COUNT(*) FROM scoreWHERE Score > S.Score)+1 ‘Rank‘FROM Score SORDER BY Score DESC

 查询结果：

任务3

项目十：行程和用户（难度：困难）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。+------------+-------------------+| Day | Cancellation Rate |+------------+-------------------+| 2013-10-01 | 0.33 || 2013-10-02 | 0.00 || 2013-10-03 | 0.50 |+------------+-------------------+

SELECT Request_at Date_Day,ROUND((SUM(IF(Status =‘completed‘,0,1))/COUNT(*)),2) Candle_RateFROM TripsWHERE Client_Id IN (SELECT Users_Id FROM Users WHERE Banned=‘No‘)OR Driver_Id IN (SELECT Users_Id FROM Users WHERE Banned=‘No‘)GROUP BY Request_at

 查询结果：