Would it be correct to add extra columns to the junction table according to normalization rules? Hello I have many to many relationship. I learning normalization rules.
I add quantity because quantity column is used only for products associated with the invoice.
My question is: Can I add extra column in junction table? Is it OK to normalization rules or is there a better solution?
yes you can add columns to a bridge table, as long as they are attributes to that for that relationship.
Customers     CustomerProducts      Products

customerId    customerId            productId
              productId
              price
              quantity
              buyDate

The columns price, quantity and buy_date, are all specific to the that entry