Adds or subtracts a specified time interval from a specified date.
DATEADD (datepart, number, date)
date is a valid date and number is the number of interval you want to add and DatePart is:
The week (wk, ww) datepart reflects changes made to SET DATEFIRST. January 1 of any year defines the starting number for the week datepart, for example: DATEPART(wk, 'Jan 1, xxxx') = 1, where xxxx is any year.
The weekday (dw) datepart returns a number that corresponds to the day of the week, for example: Sunday = 1, Saturday = 7. The number produced by the weekday datepart depends on the value set by SET DATEFIRST, which sets the first day of the week.
Example 1 of DATEADD()
select dateadd(Day, 1, Getdate()) as tomorrow
If the above query is ran on 7-july-2010 then the result will be:
Example 2 of DATEADD()
below example decreases the date by 2 months
select dateadd(mm, -2, '07-08-2010')