>that returns the number of the week from
>>a date (based on your conditions) and select a new column beased on this new UDF and add this column to the GROUP BY clause.
>
> Sorry, this part I didn't understand. Could you please tell more?

Never mind. It was not clear what's the condition on dates, so, I said you could use a user defined function (UDF).
It's the same as your between() condition in your further messages.

Vlad