Calculate difference between two dates in SQL Server

How To Find Date Difference Between Two Dates ?

DATEDIFF ( datepart , startdate , enddate )
You can use SQL Server DateDiff function to calculate difference between two dates. This delay can be calculated in days, months, years, minutes,hours or seconds.

Datepart

Is the parameter that specifies on which part of the date to calculate the difference. The following table lists dateparts and abbreviations recognized by SQL Server 2005. These dateparts and abbreviations cannot be supplied as a user-declared variable.

Datepart	Abbreviations
year	yy, yyyy
quarter	qq, q
month	mm, m
dayofyear	dy, y
day	dd, d
week	wk, ww
Hour	hh
minute	mi, n
second	ss, s
millisecond	ms

Example 1:

Select datediff (m, '20100131', '20100201')

Example 2:

Select datediff(mi, '2010-01-22 15:29:55.090' , '2010-01-22 15:30:09.153') 

Example 3:

SELECT  DATEDIFF(day, '2010-01-22 15:29:55.090', '2010-01-22 15:30:09.153')