MySQL Many to Many with additional data in intermediary table I need to create a Many to Many relationship and understand the need for an intermediate table to act as the link between the two. The understanding I have is the Group of ID's in the intermediate table should be unique to not duplicate data; is this correct?
The DB that I am designing is for a deck of cards.
I have two tables: decks and cards. The intermediary table is deck_cards.
The issue I am facing is: a deck can contain many cards but can also contain more than one of the same card.
Below is a screen shot of my current Schema. I am currently storing an additional bit of data in the column amount in the deck_cards table for a given relationship. Is this the appropriate way to approach this situation? Or, is there another intermediary table that is needed to be created?
If we have Person and School and a Person can enroll in zero to many schools and a School can enroll one to many people the many-to-many relation exists, but we would refer to the resulting entity as something like Student with its own properties (enrollment date, student id number, etc).
So outside of maybe changing the name of the entity, there's nothing wrong with that portion of the data model.
Other notes:

You need at least one alternate key on User, definitely one for Username, possibly one for Email.
You will need an alternate key on Deck, (user_id,name).
You will need an alternate key on Card, (name).