題目描述
編寫一個 SQL 查詢,獲取 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查詢應該返回 200 作爲第二高的薪水。如果不存在第二高的薪水,那麼查詢應返回 null
。
+---------------------+
| SecondHighestSalary |
+---------------------+
| 200 |
+---------------------+
思路
- 排序,取出排名第二的值
select Salary from Employee
order by Salary desc
limit 1, 1;
- group by 過濾掉相同薪水
select Salary from Employee
group by Salary
order by Salary desc
limit 1, 1;
- 當不存在第二高的薪水時,會返回空而不是
null
,做個是否爲null
的判斷
select
ifnull(
(select Salary from Employee group by Salary order by Salary desc limit 1, 1),
null
) as SecondHighestSalary;
可以簡寫爲
select
(select Salary from Employee group by Salary order by Salary desc limit 1, 1)
as SecondHighestSalary;