discount voucher how to set up using php

For this kind of feature I use a table with the following fields:

promo_code (the promo or voucher text/number the customer will enter)

promo_deduction (the percentage of the deduction)

promo_expiration (a date you want the offer to end)

promo_id (auto increment primary key)

feature_id (if you want the offer to apply to only a specific product or service, this prevents it being applied to any product/service)

Then, if PHP is performing the calculation, in your POST data you would first check to see if they entered a voucher code, then compare it to your table of valid codes and if there is a match, return the deduction amount as a variable. This is accomplished with a simple WHERE clause in your query  (...WHERE promo_code=:promo_code_entered AND promo_expiration <=:currentdate AND feature_id =:feature_id)

Then multiply the variable by the total, like so:

$total = $pretotal * $promo_deduction;

You could alternatively use Javascript to create a live response, so that when they enter a code in the voucher field, it will update the total or respond with a message that the voucher was not valid.