Looking for help to work out a subscription service schema

I'm finding it difficult to decide on a schema for a monthly subscription service. In particular, if my the credit cards table should be related to the customer or to the subscription.

The tables I currently have are the following:

   users
      id
      other fields.

   addresses
      id
      userid
      other fields

   subscriptions
      开发者_开发百科id
      userid
      other fields

   cards
      id
      userid
      last4digits

A user can only have one subscription. For now, only credit cards are accepted as a form of payment. However, that could change in the future. My schema is simplistic, but I'm afraid my setup will be a pain to alter in the future if more payment types are added.

Can you provide me with some advice please?

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Your database design should consider what types of queries you will want to execute against the data, however, without knowing more, how about introducing a Payments table:

Clients 1..* Cards

Cards 1..* Payments

Payments 1..* Subscriptions

This way in the future you can easily add other payment types, e.g. add:

Clients 1..* PaypalAccounts

PaypalAccounts 1..* Payments

Also, I'm assuming a payment can be taken for more than one subscription.