Nth Higthest Salary

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
  RETURN (
    SELECT CASE WHEN COUNT(SUB.SALARY) < N THEN NULL
                ELSE MIN(SUB.SALARY)
            END
    FROM (
        SELECT DISTINCT SALARY
        FROM EMPLOYEE
        ORDER BY SALARY DESC
        LIMIT N
        ) SUB
  );
END

// IF (condition, value_if_true, value_if_false)
SELECT IF(500<1000, "YES", "NO")
SELECT IF(500<1000, "YES", NULL)

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
  RETURN (
    SELECT IF(COUNT(SUB.SALARY) < N, NULL, MIN(SUB.SALARY))
    FROM (
        SELECT DISTINCT SALARY
        FROM EMPLOYEE
        ORDER BY SALARY DESC
        LIMIT N
        ) SUB
  );
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