Hi I have a friend who has a rental store for movies and the movies are in boxes of bulk. Let's say in a mysql database there are 29 rentals available and 3 new dvds purchase available for the same dvd, but every dvd is in a different location because there are several boxes. How can I have it so that it knows the availabe locations in the for purchase(buy) and a sepeate set of locations available for the rentals it also needs to lower the number when one goes out so that inventory is up to date and also it needs to be able to know which one is now out of inventory. so when we look on the reset it tells us which one it is?

And your problem is?

All you have described is a pretty average stock/inventory management system.