[Leetcode database 177] Get the nth highest salary in the Employee table (Salary)

Write a SQL query to get the nth highest salary in the Employee table (Salary).
+----+--------+
| Id | Salary |
+----+--------+
| 1 | 100 |
| 2 | 200 |
| 3 | 300 |
+----+--------+
For example, in the above Employee table, when n = 2, the second highest salary 200 should be returned. If there is no nth highest salary, then the query should return null.
+------------------------+
| getNthHighestSalary(2) |
+----------------- -------+
| 200 |
+------------------------+

Solution:
One, Mysql

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
declare m INT;
set m = n-1;
  RETURN (
      # Write your MySQL query statement below.
      SELECT distinct Salary FROM Employee order by salary desc limit m,1
  );
END

Index of Limit starts from 0

二、Oracle

CREATE FUNCTION getNthHighestSalary(N IN NUMBER) RETURN NUMBER IS
result NUMBER;
BEGIN
    /* Write your PL/SQL query statement below */
    select salary into result
      from (
          select salary,rank() over(order by salary desc) as rn from employee
      )a
     where rn = n;
    RETURN result;
END;

Note that select requires parameters returned by into.