LeetCode176. Second Highest Salary

Table: Employee

+-------------+------+
| Column Name | Type |
+-------------+------+
| id          | int  |
| salary      | int  |
+-------------+------+
id is the primary key column for this table.
Each row of this table contains information about the salary of an employee.

Write an SQL query to report the second highest salary from the Employee table. If there is no second highest salary, the query should report null.The query result format is in the following example.

Input: 
Employee table:
+----+--------+
| id | salary |
+----+--------+
| 1  | 100    |
| 2  | 200    |
| 3  | 300    |
+----+--------+
Output: 
+---------------------+
| SecondHighestSalary |
+---------------------+
| 200                 |
+---------------------+

select salary as SecondHighestSalary from (

  select salary, RANK () OVER (ORDER BY salary DESC) RANK from Employee

) where RANK=2

select MAX(salary) "SecondHighestSalary" from employee 

where salary < (select max(salary) from employee);

WITH  real_query  AS (

  select salary as SecondHighestSalary from (

    select salary, dense_rank() OVER (ORDER BY salary DESC) RANK from Employee

  ) where RANK=2

)

SELECT  SecondHighestSalary FROM real_query

union

select null FROM dual

WHERE NOT EXISTS(SELECT 1 FROM real_query);

https://marketing.ares.com.tw/newsletter/2015-01/oracle

https://blogs.ontoorsolutions.com/post/3_ways_to_find_sec_highest_salary/

https://www.techonthenet.com/oracle/questions/second_highest.php

https://blog.xuite.net/choubee/blog/39619596