nth-highest-salary.sql

# Time:  O(n^2)
# Space: O(n)
#
# 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.
#
CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
  RETURN (
     # Write your MySQL query statement below.
     SELECT MAX(Salary) /*This is the outer query part */
            FROM Employee Emp1
            WHERE (N-1) = ( /* Subquery starts here */
                 SELECT COUNT(DISTINCT(Emp2.Salary))
                        FROM Employee Emp2
                        WHERE Emp2.Salary > Emp1.Salary)
  );
END