SELECT DATEDIFF(days, FirstDate, SecondDate), FirstDate, SecondDate FROM MyTable
days
GETDATE
SELECT DAYCOUNT(Day, 1/1/1998, getdate())
SELECT DATEDIFF(Day, '1/1/1998')
SELECT DATEDIFF(Weeks, '1/1/1998', GetDate()) * 7
SELECT DATEDIFF (Day, '1/1/1998', GetDate())