Good afternoon I have a problem when it comes to relating data in mysql for a system that I am developing, the doubt that I have is that the company that I am working with buys its products wholesale, and sells them in the same way , but I'm looking for a way to enter the products in different levels, for example purchase: -Purchase 1 Box of Pencils containing 20 Boxes and Each box contains 12 pens, in this purchase we observed 3 levels Another example would be when buying medical pills -Buy 1 Box and each box has 20 boxes and each box has 12 blister packs and each blister 12 pads in this we see 4 levels At the time of the sale, it would be necessary to be able to make these different forms either by unit, blister, box or box. The problems I have is how to model the database knowing that we can have different levels of purchase according to the presentation you buy