Leetcode的SQL题解：185. 部门工资前三高的员工

题目

查询部门工资前三高的员工。

我用的数据库是oracle。
下面是数据表的信息。
Employee表数据：

| 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	|
|8 |	edav	|	50000	|	2	|
|9 |	easonv	|	40000	|	2	|

8、9行为我自行添加，为了更清晰展示查询结果。

创建表

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

create table Employee (
  Id number(5),
  Name varchar2(10) ,
  Salary number(5),
  DepartmentId number(5)
);

Department 表包含公司所有部门的信息。

create table Department  (
  Id number(5),
  Name varchar2(10) 
);

插入数据Employee，脚本如下

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', null);

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');

insert into Employee (ID, NAME, SALARY, DEPARTMENTID)
values ('8', 'eda', '50000', '2');

insert into Employee (ID, NAME, SALARY, DEPARTMENTID)
values ('9', 'eason', '40000', '2');

插入数据Department，脚本如下

insert into Department (ID, NAME)
values ('1', 'IT');

insert into Department (ID, NAME)
values ('2', 'Sales');

查询

以下使用四种SQL语句查出的结果，前两个是用oracle特有函数，后两个是标准SQL92写法。

你觉得哪个对？哪个性能高？

函数1 ROW_NUMBER

select Department，Employee，Salary
 from (select (ROW_NUMBER()
               over(PARTITION by t1.departmentid order by Salary desc)) lev,
              t2.name Department,
              t1.name Employee,
              t1.Salary Salary
         from Employee t1, Department t2
        where t1.departmentid = t2.id) A
where lev <= 3;

函数2 dense_rank

select D.Name Department, E.Name Employee, E.Salary Salary
	from (select Name,
														Salary,
														DepartmentId,
														dense_rank() over(partition by DepartmentId order by Salary desc) Trank
									from Employee) E
right join Department D
			on E.DepartmentId = D.id
where Trank <= 3;

通用写法1

select d.name as Department, e.name as Employee, e.salary as Salary
  from employee  e
 inner join department  d
    on e.DepartmentId = d.id
 where  (select count(distinct salary)
          from employee
         where salary > e.salary
           and departmentid = e.DepartmentId) < 3
 order by e.departmentid, Salary desc;

通用写法2

SELECT t3.name Department, t2.name Employee, t2.salary Salary
	FROM Employee t2, Department t3
WHERE t2.id NOT IN (SELECT b.id
						FROM Employee a, Employee b
						WHERE a.DepartmentId = b.DepartmentId
								AND a.salary > b.salary
								GROUP BY b.id
								HAVING COUNT(*) >= 3)
		AND t2.DepartmentId = t3.id
ORDER BY Department, t2.salary DESC;

吐槽

感兴趣的同学可以自己跑下。

我个人觉得所谓官方答案是有问题的。

官方题解如下，mysql版本：

SELECT d.Name AS 'Department', e1.Name AS 'Employee', e1.Salary
	FROM Employee e1
	JOIN Department d
			ON e1.DepartmentId = d.Id
    WHERE 3 > (SELECT COUNT(DISTINCT e2.Salary)
				FROM Employee e2
				WHERE e2.Salary > e1.Salary
			AND e1.DepartmentId = e2.DepartmentId);

改写成oracle版，加上排序：

SELECT d.Name Department, e1.Name Employee, e1.Salary
	FROM Employee e1
	JOIN Department d
			ON e1.DepartmentId = d.Id
    WHERE 3 > (SELECT COUNT(DISTINCT e2.Salary)
				FROM Employee e2
				WHERE e2.Salary > e1.Salary
			AND e1.DepartmentId = e2.DepartmentId)
	 order by d.id,salary desc

查出来的数据是与通用写法1一样的，
两个同样的85000的数据

|序号| Department | Employee | Salary |
|--- | ---- | ------- | ------------ |
|1 |	IT  |	Max   |	90000
|2 |	IT  | 	Randy |	85000
|3 |	IT  |	Joe   |	85000
|4 |	IT  |	Will  |	70000
|5 |	Sales |	Henry |	80000
|6 |	Sales |	Sam   |	60000
|7 |	Sales |	eda|	50000

这个题目出的歧义太大，如果是在考试中，应该是查出前三名、前四名的都对。

个人认为应该查出前三名应该是不包含70000这条数据的，就算是并列第二，那么就应该没有第三了，高校排名不也是这样吗？

所以私以为正确答案应该是查出这样的数据

|序号| Department | Employee | Salary |
|--- | ---- | ------- | ------------ |
|1 |	IT  |	Max   |	90000
|2 |	IT  | 	Randy |	85000
|3 |	IT  |	Joe   |	85000
|4 |	Sales |	Henry |	80000
|5 |	Sales |	Sam   |	60000
|6 |	Sales |	eda|	50000

那么，我写的四条语句中，应该是函数1及通用写法2可以满足这个条件。

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