Select SQL results grouped by weeks

I think this should do it..

Select 
ProductName,
WeekNumber,
sum(sale)
from
(
    SELECT 
    ProductName,
    DATEDIFF(week, '2011-05-30', date) AS WeekNumber,
    sale
    FROM table
)
GROUP BY
ProductName,
WeekNumber

the provided solutions seem a little complex? this might help:

https://msdn.microsoft.com/en-us/library/ms174420.aspx

select
   mystuff,
   DATEPART ( year, MyDateColumn ) as yearnr,
   DATEPART ( week, MyDateColumn ) as weeknr
from mytable
group by ...etc

This should do it for you:

Declare @DatePeriod datetime

Set @DatePeriod = '2011-05-30'

Select  ProductName,
        IsNull([1],0) as 'Week 1',
        IsNull([2],0) as 'Week 2',
        IsNull([3],0) as 'Week 3',
        IsNull([4],0) as 'Week 4',
        IsNull([5], 0) as 'Week 5'

From 
(
Select  ProductName,
        DATEDIFF(week, DATEADD(MONTH, DATEDIFF(MONTH, 0, InputDate), 0), InputDate) +1 as [Weeks],
        Sale as 'Sale'

From dbo.YourTable
-- Only get rows where the date is the same as the DatePeriod
-- i.e DatePeriod is 30th May 2011 then only the weeks of May will be calculated
Where DatePart(Month, InputDate)= DatePart(Month, @DatePeriod)
)p 
Pivot (Sum(Sale) for Weeks in ([1],[2],[3],[4],[5])) as pv

It will calculate the week number relative to the month. So instead of week 20 for the year it will be week 2. The @DatePeriod variable is used to fetch only rows relative to the month (in this example only for the month of May)

Output using my sample data: