calculate the quantity of items in stock

I currently have a search button that calls 2 tables and shows me the information i want. One column of info is Quanity. I want to be able to search for information and have the quanity of certain items keep adding on as new info comes in. For example, I get new info every week on stores and items sold. I replace the old tables with the new tables every week, but still need quantity from old page to add on to new page when i search. is this possible?

re: calculate the quantity of items in stock

nobody knows how to do this?

re: calculate the quantity of items in stock

You shouldn't be storing a calculated value or replacing your data each time. If you have a transaction table of items sold for instance which records the historical data you can calculate dynamically at any time the total sold over any period.

If you also separately store the stock bought then the quantity in stock can also be dynamically calculated by comparing the stock bought with the quantity sold.

Have a look at this tutorial and ask questions on anything you don't understand.

Database Normalisation and Table structures