184.部门工资最高的员工

题目描述

表： Employee

+--------------+---------+
| 列名          | 类型    |
+--------------+---------+
| id           | int     |
| name         | varchar |
| salary       | int     |
| departmentId | int     |
+--------------+---------+
在 SQL 中，id是此表的主键。
departmentId 是 Department 表中 id 的外键（在 Pandas 中称为 join key）。
此表的每一行都表示员工的 id、姓名和工资。它还包含他们所在部门的 id。

表： Department

+-------------+---------+
| 列名         | 类型    |
+-------------+---------+
| id          | int     |
| name        | varchar |
+-------------+---------+
在 SQL 中，id 是此表的主键列。
此表的每一行都表示一个部门的 id 及其名称。

查找出每个部门中薪资最高的员工。 按 任意顺序 返回结果表。 查询结果格式如下例所示。

示例 1:

输入：
Employee 表:
+----+-------+--------+--------------+
| id | name  | salary | departmentId |
+----+-------+--------+--------------+
| 1  | Joe   | 70000  | 1            |
| 2  | Jim   | 90000  | 1            |
| 3  | Henry | 80000  | 2            |
| 4  | Sam   | 60000  | 2            |
| 5  | Max   | 90000  | 1            |
+----+-------+--------+--------------+
Department 表:
+----+-------+
| id | name  |
+----+-------+
| 1  | IT    |
| 2  | Sales |
+----+-------+
输出：
+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT         | Jim      | 90000  |
| Sales      | Henry    | 80000  |
| IT         | Max      | 90000  |
+------------+----------+--------+
解释：Max 和 Jim 在 IT 部门的工资都是最高的，Henry 在销售部的工资最高。

SQL Schema

Drop table If Exists Employee;
Drop table If Exists Department;
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)
);
insert into Employee (id, name, salary, departmentId)
values ('1', 'Joe', '70000', '1');
insert into Employee (id, name, salary, departmentId)
values ('2', 'Jim', '90000', '1');
insert into Employee (id, name, salary, departmentId)
values ('3', 'Henry', '80000', '2');
insert into Employee (id, name, salary, departmentId)
values ('4', 'Sam', '60000', '2');
insert into Employee (id, name, salary, departmentId)
values ('5', 'Max', '90000', '1');
insert into Department (id, name)
values ('1', 'IT');
insert into Department (id, name)
values ('2', 'Sales');

答案

解法一：子查询

SELECT d.name AS `Department`, e.name AS `Employee`, e.salary AS `Salary`
FROM department d
         INNER JOIN employee e ON d.id = e.departmentId
WHERE (e.departmentId, e.salary) IN (SELECT e.departmentId, MAX(e.salary) AS `salary`
                                     FROM employee e
                                     GROUP BY e.departmentId);

解法二：排名窗口函数

SELECT d.name AS `Department`, t.name AS `Employee`, t.salary AS `Salary`
FROM department d
         INNER JOIN (SELECT name,
                            salary,
                            departmentId,
                            DENSE_RANK() OVER (PARTITION BY departmentId ORDER BY salary DESC) AS `rn`
                     FROM employee) t ON d.id = t.departmentId
WHERE t.rn = 1;