How to subtract a session value from a database table value in a recordset

I have used data assist to create a search able list of my users, and then a way to set up a bill them.

When I bill them a record in the database is made, which has their id in a id field.

Then, on the users cp, I filter that table for the records which has their id.

This way they see there bills.

I then made a PayPal button which is dynamic for the billing amount and so on.

After they pay they come back to my site where I want a simple calculation to be done.

I create a session var which they click the PayPal button for the amount.

On the success page, is there a way to take the session value, and subtract it from the another value in a recordset used to show their overall balance.

Hope I explained this well enough, if you need more info just ask.

Thanks...

something like this should do the trick:

<?php echo(floatval($row_recordsetName['ColumnName']) - floatval((isset($_SESSION['sessionName'])?$_SESSION['sessionName']:0))); ?>

I have a small issue.

When the user returns after paying for a bill, I need to change a field in the database to paid.

I want to do this on the success page. Could you tell me how to do this.

I am using the standard PayPal buttons. I thought that if I made a session value of the bill ID when the user clicks the PayPal button I could use the session on the success page to filter a record set for the bill that has been paid for, and then use the data assist to update the field on page load.

Not sure if this is possible because when I open cookies tool kit to make the session it does not see the PayPal button.

Could you tell me how to do this?

the problem with paypal payment buttons is that it is not a real time payment method.

just because the user is directed back to the success page, does not mean the payment has been made successfully. it only means that paypal has accepted the payment method and has placed the transaction in a queue to be processed with the merchant bank.

Paypal uses a system called IPN to send a post to your site with the status of the transaction once it is actually processed. you would need to create a page to accept the IPN post and update the database based on the results of the paypal IPN post.


for more details on paypal IPN see the following page:
ipn