I need help finalize my database. it is a basic POS system where I have a table for Inventory, sales and purchase. I need to set it up so that If one item is sold then 1 is removed from the stock, and If I purchase 1 item then 1 is added to the inventory. I have made the shell of it with all approperiate fields but can't seem to figure out a calculation that will let me do this.
any suggestion is much appreciated.