Leetcode day4 the highest paid employee in the Department

184. The highest paid employees in the Department

Medium difficulty

SQL framework

Employee Table contains all employee information , Each employee has its own corresponding Id, salary and department Id.

+----+-------+--------+--------------+
| Id | Name  | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1  | Joe   | 70000  | 1            |
| 2  | Jim   | 90000  | 1            |
| 3  | Henry | 80000  | 2            |
| 4  | Sam   | 60000  | 2            |
| 5  | Max   | 90000  | 1            |
+----+-------+--------+--------------+

Department The table contains information about all departments of the company .

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

Write a SQL Inquire about , Identify the highest paid employees in each department . For the above table , Your SQL The query should return the following line （ The order of the lines doesn't matter ）.

+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT         | Max      | 90000  |
| IT         | Jim      | 90000  |
| Sales      | Henry    | 80000  |
+------------+----------+--------+

explain ：

Max and Jim stay IT The wages of all departments are the highest ,Henry The highest salary is in the sales department .

Answer key ：

1、 Even the table query

Through the description of the topic, it is not difficult to see that we first need to pass the two tables DepartmentID Connect

sql Code ：

select Department.Name as Department, Employee.Name as Employee,Salary
from Employee 
left join Department 
on Employee.DepartmentId = Department.Id

The operation results are shown in the following table ：

Department	Employee	Salary
IT	Joe	70000
IT	Jim	90000
Sales	Henry	80000
Sales	Sam	60000
IT	Max	90000

Next, we can know from the meaning of the topic , As long as the salary is the highest in the Department, the employee information needs to be displayed , So we can't use max() Aggregate function when the result of the query , We need to max() As a condition of judgment , When the salary of the employees in the Department is equal to the maximum salary, we will display the information of the changed employees .

2、 Construction conditions

The maximum salary of each department can be found by group query .

select max(Salary),DepartmentId
from Employee
group by DepartmentId

Running results ：

max(Salary)	DepartmentId
90000	1
80000	2

Here we can use in Conditions to judge , When departmentid and max(Salary) Show the employee information when they are satisfied .

3、 Code implementation

sql Code

select Department.Name as Department, Employee.Name as Employee,Salary
from Employee 
left join Department 
on Employee.DepartmentId = Department.Id
where 
(Salary,Department.Id)
in
(
select max(Salary),DepartmentId
from Employee
group by DepartmentId
)

It's used here in() Pass two parameters in , It means that only when these two conditions are met can the conditions be met .

Running results :

Department	Employee	Salary
IT	Max	90000
IT	Jim	90000
Sales	Henry	80000