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 | +---------------------+
其实难度在于null值的返回,一条select的情况下需要union一个null值的记录
SELECT (SELECT DISTINCT Salary FROM Employee ORDER BY Salary DESC LIMIT 1,1) AS SecondHighestSalary;
SELECT Salary as SecondHighestSalary FROM Employee GROUP BY SecondHighestSalary UNION ALL (SELECT NULL AS SecondHighestSalary) ORDER BY SecondHighestSalary DESC LIMIT 1,1;