when invoice same item how to combine in one line

carputer

my sample invoice

custname.......

product id detail qty price

603001 harddisk 500GB. 1 1500
604001 monitor 17" 1 2900
608001 RAM 2GB. 2 400
603001 harddisk 500GB. 2 1500

i want to know how to write code that order, in line 1 and line 4 the products those have the same product id i want
combine and sum qty in one line like this sample below

603001 harddisk 500GB. 3 1500
604001 monitor 17" 1 2900
608001 RAM 2GB. 2 400

i'm sorry in language english not good
please teach me
thank you
warat in thailand

gordk

use a query with anorder by clause to supply yor data