text: # Write your MySQL query statement below
  
  ## [Problem] not able to return null if no row found
  # However, this solution will be judged as 'Wrong Answer' if there is no such second highest salary since there might be only one record in this table.
  # 1. ------------------------------------------------------------
  # SELECT IFNULL( Salary, null ) AS SecondHighestSalary
  # FROM Employee
  # # LIMIT OFFSET, COUNT
  # ORDER BY Salary DESC LIMIT 1,1;
  
  # 2. ------------------------------------------------------------
  # SELECT DISTINCT
  #     Salary AS SecondHighestSalary
  # FROM
  #     Employee
  # ORDER BY Salary DESC
  # LIMIT 1 OFFSET 1
  
  # to solve the problem, treat it as a temp table
  # SELECT
  # (
  #     SELECT Salary
  #     FROM Employee
  #     # LIMIT OFFSET, COUNT
  #     ORDER BY Salary DESC LIMIT 1,1
  # )  AS SecondHighestSalary
  # ;
  
  # IFNULL version
  SELECT
      IFNULL(
          (
              SELECT DISTINCT Salary
              FROM Employee
              # LIMIT OFFSET, COUNT
              ORDER BY Salary DESC LIMIT 1,1
          ),
          NULL
      ) AS SecondHighestSalary
  ;