Re: Pulling an ID list from a DB, then filtering that list againstanother list of ID's

Matt Babineau wrote:

Here is what I have for a layout: thing_id -> it is a hash value (md5()) I have a user session variable that is an array "thing_id's that were viewed". So each time the user click a like to view a thing_id, I note that in a session variable, so when they go back to the home page, all the things they have viewed are not shown, only the ones they have not viewed. Thing_id --------- 1 | hash_id_1 2 | hash_id_2 3 | hash_id_3 4 | hash_id_4 Viewed (Session Var) -------------------- 1 | hash_id_2 2 | hash_id_4 So when the user hits the homepage, they should get a list of 2 hash ID's hash_id_1 and hash_id_3. That is how I want this to work, I just need a slick way to compare and filter the viewed hash_id's from the complete list I am pulling form the DB. Does that help?

Yes. You only need to maintain one list, actually, the list of "things" that the user has viewed. Then, do something like this: $list = "'" . implode("','",$_SESSION['viewed_hash']) . "'"; $query = "SELECT thing FROM Thing_Table WHERE thing_hash NOT IN ($list)"; Run that query and you'll have all of the results in the table that the view has not seen. -- ---John Holmes... Amazon Wishlist: www.amazon.com/o/registry/3BEXC84AB3A5E/ PHP|Architect: A magazine for PHP Professionals – www.phparch.com