How do I make such a complicated demand (for me)on mysql and php

Hi Okay... I am out of my depth and confused and would appreciate some help to push me in the right direction. I have 3 tables in MYSQL: "users" - contains users email address and the press release categories that they wish to hear about (in usr_4). "releases" - contains press releases with a datstamp in (Ymd) format and presscatid categories - which has all the press release categories and presscatid What I want to do is send all users that have asked to receive daily updates of chosen categories the title, first 150 characters and the link back to the release, an email of the preferences that they have chosen (eg Food, Transport etc), if there is a new release in that category. I have so far managed to get the releases with a datestamp of $today and send it to my email address (hardcoded in the script) I can not work out how to get the script to step through all the press release categories on by one and which logic is needed. Do I select the cateorgies and start that end or do I select the users and the work through the categories that they have requested to hear about? Many thanks James