Department Highest Salary

The Employee table holds all employees. Every employee has an Id, a salary, 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            |
+----+-------+--------+--------------+

The Department table holds all departments of the company.

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

Write a SQL query to find employees who have the highest salary in each of the departments. For the above tables, Max has the highest salary in the IT department and Henry has the highest salary in the Sales department.

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

Naive Way: 做数据库的题真是比做算法题快多了。但还不是很熟练。

 SELECT D.name as Department, E1.name as Employee, E1.Salary as Salary  
 FROM Employee E1 join Department D  
 WHERE E1.DepartmentId = D.Id   
 AND E1.Salary >= (SELECT MAX(Salary) from Employee E2  
 WHERE E1.DepartmentId = E2.DepartmentId);  

Improved Way: