176. Second Highest Salary

Giới thiệu bài toán

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

Table: Employee

Column Name	Type
id	int
salary	int

• id is the primary key (column with unique values) for this table.
• Each row of this table contains information about the salary of an employee.

Yêu cầu

Write a solution to find the second highest salary from the Employee table. If there is no second highest salary, return null (return None in Pandas).

The result format is in the following example.

Example 1:

• Input: Employee table:

id	salary
1	100
2	200
3	300

• Output:

SecondHighestSalary
200

Example 2:

• Input: Employee table:

id	salary
1	100

• Output:

SecondHighestSalary
null

Giải quyết bài toán

SELECT (
    SELECT DISTINCT(salary) 
    FROM Employee 
    ORDER BY salary DESC 
    LIMIT 1 OFFSET 1
) AS SecondHighestSalary;

Tham khảo: https://leetcode.com/submissions/detail/1038480623/