【LeetCode】Department Highest Salary && Department Top Three Salaries

1、Department Highest Salary

Total Accepted: 367 Total Submissions: 1887 My Submissions Question Solution 

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  |
+------------+----------+--------+

【解题思路】

1、根据部门分组，同时求出部门最大Salary。
2、从雇员表选出Salary和最大值相等并且是同一部门的。
3、将DepartmentId转为Name
其实就是三张表关联。
MySQL:

# Write your MySQL query statement below
select d.Name Department, e1.Name Employee, e1.Salary from Employee e1, Department d,
(select max(Salary) Salary, DepartmentId from Employee group by DepartmentId) e2
where e1.Salary = e2.Salary 
and e1.DepartmentId = e2.DepartmentId
and d.Id = e2.DepartmentId;

2、Department Top Three Salaries 

Total Accepted: 177 Total Submissions: 896 My Submissions Question Solution 

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  |
+------------+----------+--------+

【解题思路】
这次不用group by了。
选出同一部门薪水值比当前薪水大的种类数小于3的。
从Discuss中看到的思路，借鉴。

MySQL:

# Write your MySQL query statement below
select d.Name Department, e1.Name Employee, e1.Salary 
from Employee e1, Department d where 
(select count(distinct(Salary)) from Employee e2 
where e1.DepartmentId = e2.DepartmentId and e2.Salary > e1.Salary) < 3
and e1.DepartmentId = d.Id
order by e1.DepartmentId, e1.Salary desc;