Today MTD and YTD Values

-- For Given Date 
Select A.Quantity
From Products As A
Where A.Date = '01-01-2012'

-- Month of Given Date
Select A.Quantity
From Products As A
Where Month(A.Date) = Month('01-01-2012') And Year(A.Date) = Year('01-01-2012')

-- Year of Given Date
Select A.Quantity
From Products As A
Where  Year(A.Date) = Year('01-01-2012')

declare @year int
declare @date datetime,@startdate datetime,@enddate datetime

set @date = '2012-01-01'  --

set @year = year(@date) - case when @month < 10 then 1 else 0 end

set @startdate = datefromparts(@year,10,1)
set @enddate = datefromparts(@year+1,10,1)

select products.Quantity
  from Products
 Where Products.Date >= @startdate
   and Products.Date < @enddate