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.
+------------------------+
| getNthHighestSalary(2) |
+------------------------+
| 200 |
+------------------------+此题相较于Second Highest Salary做了一些改进：
- 创建
mysql function; - 需要判断传入参数的合理性.
因此，对代码改动如下所示：
CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
DECLARE P INT DEFAULT N-1;
IF (P<0) THEN
RETURN NULL;
ELSE
RETURN (
# Write your MySQL query statement below.
SELECT IFNULL(
(
SELECT DISTINCT Salary
FROM Employee
ORDER BY Salary DESC
LIMIT P,1)
,NULL)
AS SecondHighestSalary
);
END IF;
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