SQL求员工薪水中位数（困难）_sql薪资中位数

Leetcode上的题目，记录一下。
原题连接：
https://leetcode-cn.com/problems/median-employee-salary/

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