I'm using PHP/MySQL. I'm creating a ecommerce site and i've done the shopping cart and the order system (i.e. checkout process). I have a products table that contains a attribute called 'unitsavailable'. What i want to do is every time a person makes a purchase i want to decrement the value inside the attribute 'unitsavailable' for the specific product sold so that until it reaches 0 the system can recognise that there are no more left. If anyone can help i would apreciate it very much.