[LeetCode 177] Nth Highest Salary

Write a SQL query to get the nth highest salary from the Employee table.

+----+--------+
| Id | Salary |
+----+--------+
| 1  | 100    |
| 2  | 200    |
| 3  | 300    |
+----+--------+

For example, given the above Employee table, the nth highest salary where n = 2 is 200. If there is no nth highest salary, then the query should return null.

这道题是之前那道Second Highest Salary的拓展，根据之前那道题的做法，我们可以很容易的将其推展为N，根据对Second Highest Salary中解法一的分析，我们只需要将OFFSET后面的1改为N-1就行了，但是这样MySQL会报错，估计不支持运算，那么我们可以在前面加一个SET N = N - 1，将N先变成N-1再做也是一样的：

解法一：

复制代码 CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT BEGIN SET N = N - 1; RETURN ( SELECT DISTINCT Salary FROM Employee GROUP BY Salary ORDER BY Salary DESC LIMIT 1 OFFSET N ); END 复制代码

根据对Second Highest Salary中解法四的分析，我们只需要将其1改为N-1即可，这里却支持N-1的计算，参见代码如下：

解法二：

复制代码 CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT BEGIN RETURN ( SELECT MAX(Salary) FROM Employee E1 WHERE N - 1 = (SELECT COUNT(DISTINCT(E2.Salary)) FROM Employee E2 WHERE E2.Salary > E1.Salary) ); END 复制代码

当然我们也可以通过将最后的>改为>=，这样我们就可以将N-1换成N了：

解法三：

复制代码 CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT BEGIN RETURN ( SELECT MAX(Salary) FROM Employee E1 WHERE N = (SELECT COUNT(DISTINCT(E2.Salary)) FROM Employee E2 WHERE E2.Salary >= E1.Salary) ); END