Automatic Email: Timed from Past Date

Question

Hello everyone,
I've been thinking about trying to do something, but can use some advice and resources on how to accomplish it.
I currently have a test website that accesses a db. I use php and mySQL. I host my data online too.
Users can create accounts on the site and login to their account page from home.
From the last appointment (which is inputted into the db table called appt), I would like to have an automatic email sent to everyone every three months from the last time they had an appointment as a reminder to make another one.  The email address is stored in the members info table.  Their last appointment date is stored in the appointments table.
This is a broad question right now, I know, but I have to start somewhere.
To elaborate a bit, I would like the email to be sent a week before their recommended next appointment day so they can schedule it.
So if the last time you visited was 12/16/08, an email should be sent to you this week to remind to you make your appointment for next week.
How can I figure this out?
Thanks.

Answer 1

MySQL 5.1 introduces a new feature called Events that perform specific tasks at preset times or intervals. Don't ask me how to use them, because I don't have MySQL 5.1 on my server yet. I doubt if many hosting companies have either. But, if you're interested, you can find the details in the MySQL documentation for 5.1: http://dev.mysql.com/doc/refman/5.1/en/events.html.
The way I run scheduled events at the moment is by creating scripts with Command Line Interface PHP. This is simply an ordinary PHP script that begins with a command to tell the scheduler where to find PHP. It looks something like this:
#!/usr/local/bin/php
<?php
require_once('/home/mydomain/phpclasses/dosomethingspecial.class.php');
// rest of the script that I want to run on a regular basis
?>
I then schedule the jobs using Cron. If you have cPanel in your hosting setup, you should see Cron jobs, which is where you set the schedule for the script to run.
How do you find when to send the email? As part of your script, use a SQL query to find appointments that are between 83 and 90 days old.
SELECT client_id, client_name
FROM clients
WHERE appointment >= SUBDATE(NOW(), 83) AND appointment <= SUBDATE(NOW(), 90)