We're in the process of adding a bank-like sub-system to our own shop.

We already have customers, so each will be given a sort of account and transactions of some kind will be possible (adding to the account or subtracting from it).

So we at least need the account entity, the transaction one and operations will then have to recalculate overall balances.

How would you structure your database to handle this?

Is there any standard bank system have to use that I could mock?

By the way, we're on mysql but will also look at some nosql solution for performance boost.