Adding an additional hidden field in the attributes table

Hello,

I need to create a new field in the cart_products_attributes table called item_code. I tried doing this through the SQL interface, but when I tried adding an attribute it came up with the following error:

1136 Column count doesn't match value count at row 1
in:
[insert into cart_products_attributes values ('', '2', '1', '45', '250', '', '+', '', '0', '', '+', '0', '0', '1', '', '1', '', '', '', '', '', '', '', '', '', '', '', '0')]
If you were entering information, press the BACK button in your browser and re-check the information you had entered to be sure you left no blank fields.

So I take it that I am going about it the wrong way. Can anyone help?

The purpose of this is that my client prices their product by attribute, and having a hidden item code only for back end purposes allows them to use a v look up in excel to quickly adjust any pricing that has changed.