[LeetCode] 185. Department Top Three Salaries

問題描述

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	85000	1
2	Henry	80000	2
3	Sam	60000	2
4	Max	90000	1
5	Janet	69000	1
6	Randy	85000	1
7	Will	70000	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 (order of rows does not matter).

Department	Employee	Salary
IT	Max	90000
IT	Randy	85000
IT	Joe	85000
IT	Will	70000
Sales	Henry	80000
Sales	Sam	60000

翻譯

• Employee 表格紀錄員工資訊，每位員工擁有 Id, 及所屬部門代碼。
• Department 表格紀錄公司所有部門資訊。
• 請撰寫一段 SQL 查詢，找出各部門業績排行的前三名，同名並列。

解題思維

利用 DENSE_RANK()函數以部門代號切割，業績從高至低排名
最後撈取前三名(含)，就可得出答案

解題報告

Level: Hard
Runtime: 1173 ms, faster than 80.22% of Oracle online submissions for Department Top Three Salaries.
Memory Usage: 0B, less than 100.00% of Oracle online submissions for Department Top Three Salaries.

程式完整解題

/* Write your PL/SQL query statement below */
SELECT DEPARTMENT
      ,EMPLOYEE
      ,SALARY
  FROM(SELECT DP.NAME   AS DEPARTMENT
             ,EM.NAME   AS EMPLOYEE
             ,EM.SALARY AS SALARY
             ,DENSE_RANK() OVER(PARTITION BY EM.DEPARTMENTID ORDER BY EM.SALARY DESC) AS RANK
         FROM EMPLOYEE   EM
         JOIN DEPARTMENT DP
           ON EM.DEPARTMENTID = DP.ID)
 WHERE RANK <= 3;

SQL Schema

Create table If Not Exists Employee (Id int, Name varchar(255), Salary int, DepartmentId int)
Create table If Not Exists Department (Id int, Name varchar(255))
Truncate table Employee
insert into Employee (Id, Name, Salary, DepartmentId) values ('1', 'Joe', '85000', '1')
insert into Employee (Id, Name, Salary, DepartmentId) values ('2', 'Henry', '80000', '2')
insert into Employee (Id, Name, Salary, DepartmentId) values ('3', 'Sam', '60000', '2')
insert into Employee (Id, Name, Salary, DepartmentId) values ('4', 'Max', '90000', '1')
insert into Employee (Id, Name, Salary, DepartmentId) values ('5', 'Janet', '69000', '1')
insert into Employee (Id, Name, Salary, DepartmentId) values ('6', 'Randy', '85000', '1')
insert into Employee (Id, Name, Salary, DepartmentId) values ('7', 'Will', '70000', '1')
Truncate table Department
insert into Department (Id, Name) values ('1', 'IT')
insert into Department (Id, Name) values ('2', 'Sales')