LeetCode数据库—第二高的薪水

SQL架构：

Create table If Not Exists Employee (Id int, Salary int);
Truncate table Employee;
insert into Employee (Id, Salary) values ('1', '100');
insert into Employee (Id, Salary) values ('2', '200');
insert into Employee (Id, Salary) values ('3', '300');

查看所有记录：

mysql> select * from Employee;
+------+------+--------+--------------+
| Id   | Name | Salary | DepartmentId |
+------+------+--------+--------------+
|    1 | NULL |    100 |         NULL |
|    2 | NULL |    200 |         NULL |
|    3 | NULL |    300 |         NULL |
+------+------+--------+--------------+
3 rows in set (0.00 sec)

编写一个 SQL 查询，获取 Employee 表中第二高的薪水（Salary）。
例如上述 Employee 表，SQL查询应该返回 200 作为第二高的薪水。如果不存在第二高的薪水，那么查询应返回 null。

+-----------------------------+
| SecondHighestSalary |
+-----------------------------+
| 200 |
+-----------------------------+
查询：
方法一：

mysql> select ifnull(salary,NULL) as SecondHighestSalary from
    -> (select * from employee order by salary desc)e
    -> limit 1 offset 1;
+---------------------+
| SecondHighestSalary |
+---------------------+
|                 200 |
+---------------------+
1 row in set (0.00 sec)

方法二：

mysql> select ifnull(Salary,NULL) as SecondHighestSalary from
    -> Employee e1
    -> where (select count(distinct salary) from Employee e2 where e2.salary>e1.salary)=1;
+---------------------+
| SecondHighestSalary |
+---------------------+
|                 200 |
+---------------------+
1 row in set (0.00 sec)