I use append to add another form of it and it work but then in the second column if I'll choose a product name in the second column the price in the first column will also change and it will not place any price in the second column and same in the third column and so on.. i use onchange to change the value of prices but it will just work on the 1st column. what to do with this?
here's my specific code.
http://pastebin.com/4V7eZ8bC hope you can help me.

Try like this:

var counter = 0;
$(document).ready(function () {

    // If you want to add a row at the start:

var addRow = function() {
    var newRow = $('#form-sample').clone(true);
    newRow.attr('id', counter);