Calculating the enteries of the database

I have made a project on Inventory Control System.
I have given two options ie an inward listing & issued listing.Whenever I make an entry in the inward list it gets added in the database but incase of similar entry the change in the quantity of the item should be at the same place where the earlier entry was made.
Similarly, when I issue or take any item from the database there should be deduction of the quantity in the database.Also if the same item is being taken out the change should be at the earlier place only.
Can someone please solve this problem for me? Thanks.

jagruti

This forum is intended for questions and comments about this web site, www.javaranch.com. It is not for questions about the Java language - that's what all the other forums are for. I'm moving this to the JDBC forum.