[Leetcode-database] Second Highest Salary

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

+----+--------+| Id | Salary |+----+--------+| 1 | |    | 2 | | |    3  |    |+----+--------+

For example, given the above Employee table, the second highest salary is 200 . If there is no second highest salary and then the query should return null .

Test instructions: Query the second-highest wage, no returns NULL.

Idea 1: Direct sort to go heavy, here null to return NULL, so use the Ifnull () function.

Sql:

SELECT DISTINCT ifnull ((select distinct Salary from the employee ORDER by Salary desc-limit), null) from employee;

Understand that using nested select can replace the Ifnull function:

Select (select DISTINCT Salary from the Employee order by Salary desc limit);

Idea 2: Find the biggest. And find the biggest in the rest. Because the aggregate function can return null directly

Sql:

Select Max (Salary) from the employee where Salary < (select Max (Salary) from employee);

[Leetcode-database] Second Highest Salary