In this case you still use DATEPART()

Select Acct, Item, DATEPART(week, InvDate) AS week, SUM(QtyShipped)
FROM mytable 
GROUP BY Acct, Item, DATEPART(week, InvDate)

Using SET DATEFIRST you can change the first day of the week.

Syntax

>Hi, Sergey...
>
>Thanks for your answer - unfortunately, I think I may have worded the question incorrectly.
>
>I'm basically trying to collapse shipments down to the week. I can't really explain this without giving an example...
>
>Monday, the 3rd: 10 units shipped
>Friday, the 7th: 11 units shipped
>
>Monday, the 10th, 6 units shipped
>Tuesday, the 11th, 21 units shipped
>Saturday, the 15th, 3 units shipped
>
>I'm trying to write a T-SQL query so that I can produce this result:
>
>Week ending Saturday the 8th: 21 units shipped
>Week ending Saturday the 15th: 30 units shipped
>
>Also, the week ending date for the query could be a Saturday, but could also be another day of the week. And maybe DATEPART is still the answer, though reading BOL about how to use it has me a bit confused.
>
>Thanks,
>Kevin