Database Approach - Redundant data

I have 3 tables:

products (id, name, price, etc)
orders (id, date, payment_method, etc)
shipments (id, order_id, product_id, address, etc)

My question is: It is correct to keep in shipments table product_id? I keep i开发者_JAVA技巧t here to find information about a shipped product without using orders table.

I would suggest:

products (product_id, name, price, etc)
orders (order_id, date, payment_method, etc)
orderitem (orderitem_id, order_id, product_id, ...)
shipment (shipment_id, order_id, ... )

shipment is kind of redundant - I'd add the address etc into orders...

You can do it, but be careful - if the information in table orders could change, it would be a problem - i.e. if the appropriate record in table orders changes the product_id, the database would be inconsistent.

I do use redundant columns e.g. in static dictionaries.

Also check for the NORMAL FORMS (NF) of database desing, I'm not sure if this redundancy doesn't violate some normal form. But it is up to you if you decide to keep some NF or not.

Following the principles of truth and beauty, you should not store redundant data - it's a great opportunity for bugs to occur, it's ugly, it causes confusion in the minds of future developers.

You're allowed to break the principles of truth and beauty, but only if you run into a problem you cannot solve in any other way. For instance, if you find your queries are just too slow by joining to the orders table, denormalizing the data (which is the technical name for what you're doing) is okay - if you document it and make sure all developers understand.

Just avoiding an extra join in a query doesn't seem like a good enough reason....