Let’s say we have an orders table. When a user makes changes to a record and saves them, we want to automatically calculate the value of the total field using the fields subtotal, discount and sales_tax, where discount and sales_tax are stored as percentages (i.e. a discount value of 10 means 10% of subtotal):
function tablename_before_update(&$data, $memberInfo, &$args){ // calculate total after applying discount $data['total'] = $data['subtotal'] * (1 - $data['discount'] / 100); // calculate total after applying sales tax $data['total'] = $data['total'] * (1 + $data['sales_tax'] / 100); return true;}