1. 题目

Employee 表包含所有员工信息，每个员工有其对应的工号 Id，姓名 Name，工资 Salary 和部门编号 DepartmentId 。

+----+-------+--------+--------------+
| Id | Name  | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1  | Joe   | 85000  | 1            |
| 2  | Henry | 80000  | 2            |
| 3  | Sam   | 60000  | 2            |
| 4  | Max   | 90000  | 1            |
| 5  | Janet | 69000  | 1            |
| 6  | Randy | 85000  | 1            |
| 7  | Will  | 70000  | 1            |
+----+-------+--------+--------------+

Department 表包含公司所有部门的信息。

+----+----------+
| Id | Name     |
+----+----------+
| 1  | IT       |
| 2  | Sales    |
+----+----------+

编写一个 SQL 查询，找出每个部门获得前三高工资的所有员工。

例如，根据上述给定的表，查询结果应返回：

+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT         | Max      | 90000  |
| IT         | Randy    | 85000  |
| IT         | Joe      | 85000  |
| IT         | Will     | 70000  |
| Sales      | Henry    | 80000  |
| Sales      | Sam      | 60000  |
+------------+----------+--------+
解释：IT 部门中，
Max 获得了最高的工资，
Randy 和 Joe 都拿到了第二高的工资，
Will 的工资排第三。销售部门（Sales）只有两名员工，
Henry 的工资最高，Sam 的工资排第二。

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/department-top-three-salaries
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

2. 解题

# Write your MySQL query statement below
select Department, Employee, Salary
from
(select d.Name Department, e.Name Employee, Salary,dense_rank() over(partition by d.Name order by Salary desc) rnkfrom Employee e left join Department don e.DepartmentId = d.Id
) t
where rnk <= 3 and Department is not null

or

# Write your MySQL query statement below
select Department, Employee, Salary
from
(select d.Name Department, e.Name Employee, Salary,dense_rank() over(partition by d.Name order by Salary desc) rnkfrom Employee e right join Department don e.DepartmentId = d.Id
) t
where rnk <= 3 and Employee is not null

or 使用内连接，自动去除 null 的行

select Department, Employee, Salary
from
(select d.Name Department, e.Name Employee, Salary,dense_rank() over(partition by d.Name order by Salary desc) rnkfrom Employee e join Department don e.DepartmentId = d.Id
) t
where rnk <= 3

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