题目:编写一个 SQL 查询,获取 Employee 表中第二高的薪水(Salary)
+----+--------+
| Id | Salary |
+----+--------+
| 1 | 100 |
| 2 | 200 |
| 3 | 300 |
+----+--------+
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 |
+---------------------+
SQL:
select min(salary) as "SecondHighestSalary"
from (select salary, row_number() over(order by salary desc) rn
from (select distinct Salary from Employee))
where rn != 1
and rn <= 2
rn!=1是为了防止Table中只有一条数据。
当where条件不成立时,min(salary)的结果是空值,聚合函数为空的时候返回null
具体题目详情见:https://leetcode-cn.com/problems/second-highest-salary/