LeetCode185. All employees with the top three highest wages in the Department (MySQL)

Employee Table contains all employee information , Each employee has his / her work number Id, full name Name, Wages Salary And department number 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 The table contains information about all departments of the company .

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

Write a SQL Inquire about , Find out all the employees who get the top three salaries in each department . for example , According to the table given above , Query results should be returned ：

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

explain ：

IT In the Department ,Max Got the highest wage ,Randy and Joe All got the second highest salary ,Will The third highest salary . Sales Department （Sales） There are only two employees ,Henry The highest salary ,Sam The second highest salary .

---

Method 1

Ideas ： First sub department , Sort the salary of each department rank, Then output to each department rank<=3 Employee information

Sort method step by step ：LeetCode 178. Score ranking （Mysql）

select 
	Department,
	Employee,
	Salary
from (
	select 
		d.Name as Department,
		e.Name as Employee,
		e.Salary as Salary,
		(select count(distinct Salary) from Employee where Salary >= e.Salary and DepartmentId = e.DepartmentId) as `rank`
	from Employee e join Department d on e.DepartmentId = d.Id 
	group by e.DepartmentId,e.Name,d.Name
	order by e.Salary desc
) res where res.`rank` <=3;

Method 2

Ideas ： In front of the company 3 A high salary means no more than 3 The salary is bigger than these .

select
    d.Name as Department, e1.Name as Employee, e1.Salary
from
    Employee e1 join Department d on e1.DepartmentId = d.Id
where
    3 > (select
            COUNT(distinct e2.Salary) 
            from Employee e2 
            where e2.Salary > e1.Salary 
            and e1.DepartmentId = e2.DepartmentId );