second-highest-salary.sql

# Time:  O(n)
# Space: O(1)
#
# Write a SQL query to get the second highest salary from the Employee table. Alias Salary as SecondHighestSalary.
#
# +----+--------+
# | 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.
#
# Write your MySQL query statement below
SELECT (SELECT MAX(Salary) FROM Employee WHERE Salary NOT IN (SELECT MAX(Salary) FROM Employee)) SecondHighestSalary;
# or
SELECT (SELECT Salary FROM Employee GROUP BY Salary ORDER BY Salary DESC LIMIT 1,1) SecondHighestSalary;