Hi,
To add days from dates in SQL Server, have a look at the
DATEDIFF function.
Which can be used like:
SELECT
dateColumn,
DATEADD(day,-7,dateColumn)
FROM
yourTable
...
UPDATE:
In your query, I would use it something like this:
SET DATEFORMAT mdy;
DECLARE @StartDate DATETIME = '9/1/2010';
DECLARE @EndDate DATETIME = DATEADD(day, 14, @StartDate);
SELECT
Customer_Transaction.Order_Number,
Customer_Purchased.ProductID,
Customer_Purchased.productName,
Customer_Purchased.Branch,
Customer_Purchased.quantity,
Customer_Transaction.Total_Purchased,
Customer_Purchased.Date_Purchased
FROM
Customer_Purchased INNER JOIN
Customer_Transaction
ON Customer_Purchased.Item_Purchased_Number = Customer_Transaction.Item_Purchased_Number
WHERE
(Customer_Purchased.Branch = 'SM Dasmariñas')
AND
(Customer_Purchased.Date_Report BETWEEN @StartDate AND @EndDate)
Oh,I've not tested, or ran the above query through a parser, so it probably won't work 'as is', but should give you a start.
Hope it helps.