[LeetCode] 177. Nth Highest Salary
grandyang opened this issue · comments
Write a SQL query to get the n th highest salary from the Employee
table.
+----+--------+
| Id | Salary |
+----+--------+
| 1 | 100 |
| 2 | 200 |
| 3 | 300 |
+----+--------+
For example, given the above Employee table, the n th highest salary where n = 2 is 200
. If there is no n th 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 INT
BEGIN
SET N = N - 1;
RETURN (
SELECT DISTINCT Salary FROM Employee GROUP BY Salary
ORDER 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 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
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 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
类似题目:
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