LeetCode：Database 13.员工薪水中位数

Posted 2021-05-16 Xiao Miao

要求：请编写SQL查询来查找每个公司的薪水中位数。挑战点：你是否可以在不使用任何内置的SQL函数的情况下解决此问题？

Employee 表：

+-----+------------+--------+
|Id   | Company    | Salary |
+-----+------------+--------+
|1    | A          | 2341   |
|2    | A          | 341    |
|3    | A          | 15     |
|4    | A          | 15314  |
|5    | A          | 451    |
|6    | A          | 513    |
|7    | B          | 15     |
|8    | B          | 13     |
|9    | B          | 1154   |
|10   | B          | 1345   |
|11   | B          | 1221   |
|12   | B          | 234    |
|13   | C          | 2345   |
|14   | C          | 2645   |
|15   | C          | 2645   |
|16   | C          | 2652   |
|17   | C          | 65     |
+-----+------------+--------+
表有三列：员工Id，公司名和薪水。

Result Table：

+-----+------------+--------+
|Id   | Company    | Salary |
+-----+------------+--------+
|5    | A          | 451    |
|6    | A          | 513    |
|12   | B          | 234    |
|9    | B          | 1154   |
|14   | C          | 2645   |
+-----+------------+--------+

分析：
1.需要求出每个公司的工资中位数，首先使用开窗函数row_number()进行分组和排序
2.使用窗口聚合函数count()求出每个分组的总员工数
3.最后筛选条件为中位数工资的序号等于总员工数/2,总员工数/2+1,以及总员工数/2+0.5

SQL语句：

select id,company,salary from 
(
select id,company,salary,
row_number() over(partition by company order by salary) as r,
count(id) over(partition by company) as c1 from Employee 
) a 
where r in (c1/2,c1/2+1,c1/2+0.5);