问题：

Write a SQL query to get the nth highest salary from the Employee table.

+----+--------+| Id | Salary |+----+--------+| 1  | 100    || 2  | 200    || 3  | 300    |+----+--------+

For example, given the above Employee table, the nth highest salary where n = 2 is 200. If there is no nth highest salary, then the query should return null.

+------------------------+| getNthHighestSalary(2) |+------------------------+| 200                    |+------------------------+

① 这道题是之前那道Second Highest Salary的拓展，根据之前那道题的做法，我们可以很容易的将其推展为N，根据对Second Highest Salary中①的分析，我们只需要将OFFSET后面的1改为N-1就行了，可以在前面加一个SET N = N - 1，将N先变成N-1。1019 ms

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT

BEGIN   SET N = N - 1;   RETURN (       SELECT Salary FROM Employee       GROUP BY Salary       ORDER BY Salary DESC       LIMIT 1       OFFSET N   ); END

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT

BEGIN   SET N = N - 1;   RETURN (       SELECT DISTINCT Salary FROM Employee       ORDER BY Salary DESC       LIMIT 1       OFFSET N   ); END

② 根据对Second Highest Salary中④的分析，我们只需要将其1改为N-1即可。2278 ms

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT

BEGIN   RETURN (       SELECT MAX(e1.Salary) FROM Employee E1       WHERE N - 1 =       (SELECT COUNT(DISTINCT(E2.Salary)) FROM Employee E2         WHERE E2.Salary > E1.Salary)   ); END