Textbox Value To Increment Based On Mysql Query?

i am trying to insert/save the listview item/s on the database.what i am trying to do now is if the product is being entered/saved for the first time.the fcode should be 1, and increments after that.i have a combo box and a text box.the combo box items are from the database [ product table ]

let say user choose product 1

and the list view has 2 items [ a, b ]

and then save

the table would look like

fcode -- prod_id -- prod_name -- item
1 1 product 1 a

1 1 product 1 b[code]......