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.
answer:1）SELECT MAX(Salary) as SecondHighestSalary FROM Employee WHERE Salary < (SELECT MAX(Salary) FROM Employee);
2）SELECT DISTINCT Salary FROM Employee ORDER BY Salary DESC LIMIT 1,1; #非原创
ps:limit 1,1 第一个1是表示第二行，第二个1表示从第二行开始往后输出几行。limit 1,1表示只输出第二行。
