Plz help
i want to create a ERD, but a problem is appear
a company want can buy n type product, and a product can sold to many company. the relationship is M:N, it's easy.
But in one day, this company buy this product more than one time a day! i don't know the method to show?
Another question, if i have a mutivalue attribute of a relationship, how can i map it to the data model?