You can use DATEPART() function

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

>Hi, all...
>
>I have a file with daily invoice information. I need to be able to
>run a query that groups the data by account, product, and a specific
>day of the week.
>
>My invoice file might read as follows:
>
>Acct C(10)
>Item C(10)
>InvDate SmallDateTime
>QtyShipped Numeric
>
>Suppose I wanted to build a query that would group by acct, item, for
>each week ending Sunday. Is there a specific DATE function I can use
>in a SQL SELECT...GROUP BY so that I can summarize by a specific day
>of the week?
>
>Thanks in advance,
>Kevin