176.Second-Highest-Salary.md

176. Second Highest Salary

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题目地址

https://leetcode.com/problems/second-highest-salary/

题目描述

SQL Schema
Write a SQL query to get the second highest salary from the Employee table.

+----+--------+
| Id | Salary |
+----+--------+
| 1  | 100    |
| 2  | 200    |
| 3  | 300    |
+----+--------+
For example, given the above Employee table, the query should return 200 as the second highest salary. If there is no second highest salary, then the query should return null.

+---------------------+
| SecondHighestSalary |
+---------------------+
| 200                 |
+---------------------+

代码

Approach #1 Using sub-query and LIMIT clause

However, this solution will be judged as 'Wrong Answer' if there is no such second highest salary since there might be only one record in this table. To overcome this issue, we can take this as a temp table.

# Write your MySQL query statement below
SELECT DISTINCT
	Salary AS SecondHighestSalary
FROM
	Employee
ORDER BY Salary DESC
LIMIT 1 OFFSET 1


## To overcome this issue, we can take this as a temp table.
SELECT
    (SELECT DISTINCT
            Salary
        FROM
            Employee
        ORDER BY Salary DESC
        LIMIT 1 OFFSET 1) AS SecondHighestSalary
;

Approach #2 Using IFNULL and LIMIT clause

Another way to solve the 'NULL' problem is to use IFNULL funtion as below.

SELECT
	IFNULL(
  	(SELECT DISTINCT Salary 
    FROM Employee
    ORDER BY Salary DESC
    LIMIT 1 OFFSET 1),
    NULL) AS SecondHightestSalary