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 |
+---------------------+
开始思路,倒叙排列Salary不重复的数据,再用limit 选择第二个即可:.
select DISTINCT Salary as SecondHighestSalary from Employee order by Salary DESC limit 1 offset 1
可是当不存在数据时,返回的是空,并不是null。
在外层再嵌套一个select,即:
select (select DISTINCT Salary from Employee order by Salary DESC limit 1 offset 1) as SecondHighestSalary