【sql】第N高的薪水 Nth Highest Salary

为什么80%的码农都做不了架构师？>>>   

问题：

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 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①的分析，我们只需要将OFFSET后面的1改为N-1就行了，可以在前面加一个SET N = N - 1，将N先变成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 根据对Second Highest Salary中④的分析，我们只需要将其1改为N-1即可。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

转载于:https://my.oschina.net/liyurong/blog/1570554