[LeetCode]-DataBase-Department Top Three Salaries

The Employee table holds all employees. Every employee has an Id, 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            |
| 5  | Janet | 69000  | 1            |
| 6  | Randy | 85000  | 1            |
+----+-------+--------+--------------+

The Department table holds all departments of the company.

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

Write a SQL query to find employees who earn the top three salaries in each of the department. For the above tables, your SQL query should return the following rows.

+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT         | Max      | 90000  |
| IT         | Randy    | 85000  |
| IT         | Joe      | 70000  |
| Sales      | Henry    | 80000  |
| Sales      | Sam      | 60000  |
+------------+----------+--------+

需求：查询每个部门，工资前三高的员工

-- 有点难，没解出来，参考LeetCode上的答案
-- 解法一、
select D.Name as Department, E.Name as Employee, E.Salary as Salary
from Employee E, Department D
where (select count(distinct(Salary)) from Employee
where DepartmentId = E.DepartmentId and Salary > E.Salary) in (0, 1, 2)
and
E.DepartmentId = D.Id
order by E.DepartmentId, E.Salary DESC;

-- 解法二、
-- 一、先查询出按 部门ID升序 工资降序 排列的数据
-- 二、把(一)查询出来的数据，再关联employee表
-- 三、再对每条工资进行统计，DISTINCT的作用是查询出并列的工资的员工
SELECT D.Name AS Department, E.Name AS Employee, E.Salary AS Salary
FROM Employee E, Department D
WHERE 1=1 AND (SELECT COUNT(DISTINCT(Salary)) FROM Employee
WHERE DepartmentId = E.DepartmentId AND Salary > E.Salary) < 3
AND E.DepartmentId = D.Id
ORDER BY E.DepartmentId, E.Salary DESC;