Execute the following Microsoft SQL Server Transact-SQL (T-SQL) script in Management Studio (SSMS) Query Editor, SQLCMD or other client software to demonstrate the use of DATEDIFF to calculate the unit time (day, hour, minute, etc.) difference between two dates. The earliest date ( '1900-01-01 00:00:00.000' ) in SQL Server 2005 is the default date or base date. The number 0 casts as the base date.

USE AdventureWorks
GO


declare @Now datetime

declare @DefaultDate datetime

set @Now = getdate()

--set it to '1900-01-01 00:00:00.000'
set @DefaultDate = convert(datetime, 0);

with cteMinutes
as
(
select DateDiff(minute, @DefaultDate , @Now) as MinutesDelta

)

select
@DefaultDate as DefaultDate,
@Now as CurrentDatetime,
MinutesDelta / (24*60) as DaysDelta,
MinutesDelta / 60 as HoursDelta,
MinutesDelta as MinutesDelta
from cteMinutes

go