Я думаю, что-то подобное сработает.
from s in SALES_PRODUCT_DETAILS
join p in PRODUCT_NAME on s.PRODUCT_ID equals p.ID
where SALES.Any(sales =>
sales.SALES_DATE >= new DateTime(2011, 11, 13) &&
sales.SALES_DATE <= new DateTime(2011, 11, 16) &&
sales.SALES_ID == s.SALES_ID)
group s by new { s.PRODUCT_ID, p.NAME } into g
select new
{
g.Key.Name,
g.Key.PRODUCT_ID,
PRODUCT_SALES = g.Sum(x => x.SALES_PRICE)
}