ISNULL 两种写法，得到两种结果，返回空记录与null

select isnull(salary,null) as SecondHighestSalary

from

employee

order by salary desc

offset 1 rows

fetch next 1 rows only

 

结果是空记录

select isnull((

select salary

from

employee

order by salary desc

offset 1 rows

fetch next 1 rows only)

,null) as SecondHighestSalary

 

结果是null