MySQL Schema: Book Purchasing

[idire]

I have a book purchasing system that I am trying to produce.

 

 

So far I have these tables:

 

 

book { bookid (PK), creator, title, isbn, price, genre}

purchase { purchase_id (PK), user_id (FK), book_id (FK), date }

user { user_id (PK), username, name, balance }

 

http://i34.tinypic.com/30uakw2.png

 

1)

 

I need to be able to record a users purchases, how should I be storing a purchase where a user buys more than one item at a time:

 

two rows in purchases table

 

OR rename purchases to orders, and make another table that links in purchases to books and orders.

 

Its important I get this right in order to satisfy question 2.

 

2)

 

I need to write PHP that recommends other books for a user to purchase.

 

I figure I could do this by:

 

a) genre

b) the most popular purchased in the genre a user already purchased

c) what other users bought when they bought a book you have bought.

 

Is this ok, and what other tables would I need to make this process more efficient?

 

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Thanks