Update med datediff

Jeg har følgende T-sql, og ønsker at smide det ind i en Update men hvordan gør jeg det mest optimalt.

Select datediff(d, [Employment Date], getdate()) As [Days of Employment]
from fEmployee
Where Status = 'Active'

Select datediff(d, [Employment Date], [Termination Date]) As [Days of Employment]
from fEmployee
Where Status = 'Terminated'