sql server 2008 - DATEADD(MONTH, DATEDIFF(MONTH, 0, GETDATE()), 0) Can someone explain me this

Question

DATEADD(MONTH, DATEDIFF(MONTH, 0, GETDATE()), 0)

Can someone explain me this.

Answer 1

this will give you the first of the month for a given date

inner select select DATEDIFF(MONTH, 0, GETDATE()) will give the number of months from 1900-01-01

here it is 1350

this will be add to 1900-01-01 , but only the months

select DATEADD(MONTH,1350,0) will give 2012-07-01 00:00:00.000

which is the start of the current month.

I think this is the most efficient way to find the starting of a month for any given date.