res.txt

-- Write a SQL query to get the second highest salary from the Employee table.

-- +----+--------+
-- | Id | Salary |
-- +----+--------+
-- | 1  | 100    |
-- | 2  | 200    |
-- | 3  | 300    |
-- +----+--------+
-- For example, given the above Employee table, the second highest salary is 200. If there is no second highest salary, then the query should return null.

# Note @hijiangtao
# You should rename the result header as SecondHighestSalary. 
# NOT IN condition will consume much more time than < condition
# Note @hijiangtao

# Write your MySQL query statement below
SELECT MAX(Salary) AS "SecondHighestSalary" FROM Employee
WHERE Salary < (SELECT MAX(Salary) FROM Employee )

# Another solution
SELECT MAX(Salary) AS "SecondHighestSalary" FROM Employee
WHERE Salary NOT IN (SELECT MAX(Salary) FROM Employee )