A good and flexible database schema illustrating e-commerce products and their rates management is required.
Ecommerce transactions are not ideally suited for document databases, however. Relational databases work much better for transactional data. MongoDB, CouchDB, and Redis are examples of document databases that are used by stores.
A database system helps e-commerce sites pinpoint potential customers based on compiled information. Marketing teams can use customer data that is stored within the database to create targeted lists that will be used for directing marketing efforts.
I agree with Chris Roberts, OSCommerce is a good place to start as well as DatabaseAnswers.org.
Hope that helps.
I'm sure there are many examples about - try looking at some open source shopping cart tools.
As a general point, though, I think there are so many ways that a product pricing and discount / gift voucher system could work that finding a database schema that works for every possibility is unlikely!
Perhaps you can save yourself some heartache by refining the requirements a little?
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