LeetCode 184. 部门工资最高的员工

Employee 表包含所有员工信息，每个员工有其对应的 Id, salary 和 department Id。

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

Department 表包含公司所有部门的信息。

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

编写一个 SQL 查询，找出每个部门工资最高的员工。例如，根据上述给定的表格，Max 在 IT 部门有最高工资，Henry 在 Sales 部门有最高工资。

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

思路1：通过连表，判断相应的最高工资

select d.name as Department,e.name as Employee,e.Salary
from Department as d,Employee as e
where d.Id=e.DepartmentId and e.Salary=(Select max(Salary) from Employee where DepartmentId=d.Id)

思路2：通过group by 把每个部门的最高工资查出来，再通过连表

SELECT
d.`Name` AS Department ,
e.`Name` AS Employee ,
e.Salary
FROM (SELECT departmentId,max(Salary) AS Salary FROM employee GROUP BY DepartmentId) AS x,
employee AS e,department AS d
WHERE x.departmentId=e.DepartmentId and x.Salary=e.Salary and e.DepartmentId=d.Id