【sql】第N高的薪水 Nth Highest Salary

問題：

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                    |
+------------------------+

① 這道題是以前那道Second Highest Salary的拓展，根據以前那道題的作法，咱們能夠很容易的將其推展爲N，根據對Second Highest Salary中①的分析，咱們只須要將OFFSET後面的1改成N-1就好了，能夠在前面加一個SET N = N - 1，將N先變成N-1。1019 ms

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

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

② 根據對Second Highest Salary中④的分析，咱們只須要將其1改成N-1便可。2278 ms

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
  RETURN (
      SELECT MAX(e1.Salary) FROM Employee E1
      WHERE N - 1 =
      (SELECT COUNT(DISTINCT(E2.Salary)) FROM Employee E2
        WHERE E2.Salary > E1.Salary)
  );
END