SQL:
CREATE TABLE [dbo].[Sales](
	[Sale] [money] NULL,
	[SaleDate] [datetime] NULL
) ON [PRIMARY]
GO
 This will automatically check the last 7 days collection
SELECT SUM(SALE) AS Total FROM Sales
WHERE Saledate <= GETDATE() 
AND Saledate >=  DATEADD(day,-7, GETDATE())
Thank You.