SQL实现LeetCode(177.第N高薪水) SQL实现LeetCode(177.第N高薪水)

[LeetCode] 177.Nth Highest Salary 第N高薪水 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：

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INTBEGINSET N = N - 1; RETURN (SELECT DISTINCT Salary FROM Employee GROUP BY SalaryORDER BY Salary DESC LIMIT 1 OFFSET N); END

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：

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INTBEGINRETURN (SELECT MAX(Salary) FROM Employee E1WHERE N - 1 =(SELECT COUNT(DISTINCT(E2.Salary)) FROM Employee E2WHERE E2.Salary > E1.Salary)); END

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：

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INTBEGINRETURN (SELECT MAX(Salary) FROM Employee E1WHERE N =(SELECT COUNT(DISTINCT(E2.Salary)) FROM Employee E2WHERE E2.Salary >= E1.Salary)); END

类似题目：
Second Highest Salary
参考资料：
https://leetcode.com/discuss/88875/simple-answer-with-limit-and-offset
https://leetcode.com/discuss/63183/fastest-solution-without-using-order-declaring-variables
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