[LeetCode]-DataBase-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  |
+------------+----------+--------+

需求：查询每个部门工资最高的员工

CREATE TABLE Employee(
Id TINYINT UNSIGNED,
Name VARCHAR(20),
Salary DECIMAL(10,2),
DepartmentId TINYINT
)ENGINE=MyISAM CHARSET=utf8;
CREATE TABLE Department(
Id TINYINT UNSIGNED,
Name VARCHAR(20)
)ENGINE=MyISAM CHARSET=utf8;

SELECT b.nm,a.Name,a.salary
FROM employee a INNER JOIN (
SELECT t2.Id,t2.Name nm,MAX(t1.salary) sal
FROM employee t1 INNER JOIN department t2 ON t1.DepartmentId=t2.Id
GROUP BY t1.DepartmentId
)b ON a.salary=b.sal AND a.DepartmentId=b.Id