---

Syntax:

DATEADD (datepart, NumberToAdd, date)

DATEADD (datepart, NumberToAdd, date) - Returns the DateTime, after adding specified NumberToAdd, to the datepart specified of the given date.

DatePart	Abbreviations
year	yy, yyyy
quarter	qq, q
month	mm, m
dayofyear	dy, y
day	dd, d
week	wk, ww
weekday	dw
hour	hh
minute	mi, n
second	ss, s
millisecond	ms
microsecond	mcs
nanosecond	ns
TZoffset	tz
ISO_WEEK	isowk, isoww

Code:

Select DateAdd(DAY, 20, '2012-08-30 19:45:31.793') 
 
Select DateAdd(DAY, -20, '2012-08-30 19:45:31.793') 
 

Output:

The above code will produce the following result-

2012-09-19 19:45:31.793
2012-08-10 19:45:31.793

---