Nth Highest Salary

考察sql中函数使用，表内自连接排序，可以得到rank。
https://leetcode.com/problems/nth-highest-salary/

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT BEGIN RETURN ( SELECT DISTINCT A.Salary FROM (SELECT E2.Id,E2.Salary,COUNT(1) AS RANK FROM (SELECT DISTINCT Salary FROM Employee) E1 INNER JOIN Employee E2 ON E1.Salary>=E2.Salary GROUP BY E2.Id,E2.Salary) A WHERE A.RANK=N );
END