Rookie a database, the design that I was to add new products at the same time to the inventory list at the same time to add the goods quantity is zero, then the number of inventory changes depends on eight tables, storage table (warehouse id is a primary key column in it is whether the invoicing, only is the invoicing status in the main table can make the inventory quantity change, if cancel the check inventory quantity will change) schedule of put in storage (warehousing id key commodity id number) and six table storage return table and warehousing tables, sales of the main table and schedule of sales, sales returns table with sales return schedule is similar,