176. Second Highest Salary

```

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

```

 

배워야할점. OFFSET, LIMIT1으로 제한하기.

SELECT 두번쓰면서 null값 알아내기.

DISTINCT로 복수없애기.