Database design: How do i connect these two tables of my database in a normalisation way I want to let a  user create a food schedule(schema table) let him create his own food (userProduct) or choise from the supermarkets(supermarketproduct)

the user should be able to make many food schedules(schemas) and should be able to include many userproducts or many supermarketproducts. Both of them can be in one food schedule but, i do not know how to implement an many to many relationship with this because if i include both userproduct and supermarket product one of them will always be null.



Solution:
I would have a combined Product table with all common elements (name, protein, etc) and this would tie to the food schedules.  Then there would be two additional tables for ProductUser and ProductMarket that would refer back to the main Product table.  No nulls needed and it's nice and normalized.