如何在长查询中只检索更新的产品?

I have build an xml/aspx page that retrieves all rows in a producttable through sql server. This page is used as an xmlfeed. This xml displays productdetails like name, price and stock etc. Because the query is timeconsuming I would like to only retrieve the rows that have been changed( stock for example). What is the way to go about this in sql server?I have build an xml/aspx page that retrieves al