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 |
+————+———-+——–+

使用环境是MYSQL ，查询时长970ms

SELECT d.name,
e.name,
e.salary
FROM Employee AS e INNER JOIN
Department AS d
INNER JOIN (SELECT e2.departmentid AS depId,
Max(salary) AS depSal
FROM Employee AS e2
GROUP BY departmentid) AS t
ON e.departmentid = t.depId
AND e.salary = t.depSal AND e.departmentid = d.id;