177. Nth Highest Salary，mysql limit传参用法

mysql limt后面是支持动态参数的，但是不支持表达式形式

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
  SET N = N - 1 ;
  RETURN (
      # Write your MySQL query statement below.
      select distinct salary from employee order by salary desc limit N,1
  );

END