weeks

Anyone know offhand a way to organize the output from a query by week? I'm writing a work log app and I want the admin to see everyone's work ordered first by lastname, and then by date. But only want that week's data to show up, and maybe a dropdown with previous weeks available. Don't go thinking about an answer, cuz I'm doing that, but if anyone already knows how to solve this problem or part of it, lemme know. Thanks once again. Jason