ISNULL 兩種寫法，得到兩種結果，返回空記錄與null

select isnull(salary,null) as SecondHighestSalary

from

employee

order by salary desc

offset 1 rows

fetch next 1 rows only

結果是空記錄

select isnull((

select salary

from

employee

order by salary desc

offset 1 rows

fetch next 1 rows only)

,null) as SecondHighestSalary

結果是null