【leetcode Database】185. Department Top Three Salaries

梦里梦外; 2022-07-19 01:52 112阅读 0赞

题目：

The `Employee` table holds all employees. Every employee has an Id, and there is also a column for the department Id.

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

The `Department` table holds all departments of the company.

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

Write a SQL query to find employees who earn the top three salaries in each of the department. For the above tables, your SQL query should return the following rows.

+------------+----------+--------+
    | Department | Employee | Salary |
    +------------+----------+--------+
    | IT         | Max      | 90000  |
    | IT         | Randy    | 85000  |
    | IT         | Joe      | 70000  |
    | Sales      | Henry    | 80000  |
    | Sales      | Sam      | 60000  |
    +------------+----------+--------+

解析：

首先，按照部门Id和Salary对Employee表进行排序；之后，添加rank字段，为工资顺序序号。最后，再和Department表连接，得到最终数据。代码如下：

# Write your MySQL query statement below
    SELECT d.Name AS Department, e.Name AS Employee,e.Salary AS Salary FROM 
     (SELECT Name,Salary,DepartmentId,
     @Rank:=IF(@DepId != DepartmentId,1,IF(@Sal = Salary,@Rank,@Rank+1)) AS RANK,
     @DepId:=DepartmentId,
     @sal:= Salary FROM 
     (SELECT Name,Salary,DepartmentId FROM Employee ORDER BY DepartmentId,Salary DESC) t,
     (SELECT @Rank := 0, @DepId := NULL, @sal := NULL) r) e 
     INNER JOIN Department d ON e.DepartmentId = d.Id WHERE e.Rank <=3;