部门工资前三高的所有员工 - LeetCode

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。

通用答案：

select
    d.Name as 'Department',
    e.Name as 'Employee',
    e.Salary as 'Salary'
from Employee e 
join Department d
    on e.DepartmentId = d.Id
where 3 > (
    select 
        count(distinct e2.Salary)
    from Employee e2
    where e2.DepartmentId = e.DepartmentId
        and e2.Salary > e.Salary
)

MySQL解答：

# Write your MySQL query statement below

select
    d.Name as Department,
    temp.Name Employee,
    temp.Salary
from
    Department d left join
    (select
        e.DepartmentId,
        e.Name,
        @curRank := if (@prevDept = DepartmentId, if(@prevSal = e.Salary, @curRank, @curRank + 1), 1) as Rank,
        @prevSal := e.Salary as Salary,
        @prevDept := e.DepartmentId
    from Employee e,
    (select @prevDept := null, @curRank := 0, @prevSal := null) t
    order by e.DepartmentId, e.Salary desc
    ) temp on d.Id = temp.DepartmentId
where temp.Rank <= 3

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/department-top-three-salaries

: )