Modified code:

declare @D1 datetime, @D2 datetime

select @d1 = '1/30/2000 11:59:59 pm', @d2 = '1/31/2000 12:00:01 am'

select datepart(year, @d2-@d1)-1900 as years,

datepart(month, @d2-@d1)-1 as months,

datepart(day, @d2-@d1)-1 as days,

datepart(hour, @d2-@d1) as hours,

datepart(minute, @d2-@d1) as minutes,

datepart(second, @d2-@d1) as seconds,

datepart(millisecond, @d2-@d1) as milliseconds

Tried it with:

1 Jan 2000 11:59:59 PM and 2 Jan 2000 12:00:01 AM

1 Jan 1800 and 1 Jan 1900

28 Feb 2008 and 1 Mar 2008 -- To test for leap years

12 Dec 2007 and 12 Dec 2007 -- To test for 0

12 Dec 2007 and 12 Dec 2008

Stopped there. The first 4 worked perfectly. The last one gave back 1 year and 1 day. It's because of the leap year, since the Date2-Date1 float calculation gives 2 Jan 1901. Makes the whole thing not work without various Case statements.