leetcode 176. Second Highest Salary

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.

找到表中第二大的值

注意查询出来的列名为"SecondHighestSalary",如果没有第二大的值返回null

select IFNULL (
	(select Salary 
	from Employee
	group by Salary
	order by Salary DESC
	limit 1,1),null
) as SecondHighestSalary