Complicated database design

Question

We have a situation in a database design in our company. We are trying to figure out the best way to design the database to store transactional data. I need expert’s advice on the best relational design to achieve it. Problem: We have different kind of “Entities” in our system, for example; Customers, Services, Dealers etc. These Entities are doing transfer of funds between each other. We need to store the history of the transfers in database.

Solutions:

1. One table of transfers and another table to keep “Accounts” information. There are three tables “Customers”, “Services”, “Dealers”. There is another table “Accounts”. An account can be related to any of the “Entities” mentioned above; it means (and that’s the requirement) that logically there should be a one-to-one relationship to/from Entities and Accounts. However, we can only store the Account_ID in the Entities table, but we cannot store the foreign key of Entities in Accounts table. Here the problem happens in terms of database design. Because if there is a customer’s account, it is not restricted by the database design to not be stored in Services table etc. Now we can keep all transfers in one table only since Accounts are unified among all the entities.
2. Keep the balance information in the table primary Entities table and separate tables for all transfers. Here for all kind of transfers between the entities, we are keeping separate tables. For example, a transfer between a Customer and Service provider will be stored in a table called “Spending”. Another table will have transfer data for transfer between Service and Dealers called “Commission” etc. In this case, we are not storing all the transfers of the funds in a single table, but the foreign keys are properly defined since the tables “Spending” and “Commission” are only between two specific entities.

According to the best practices, which one of the above given solutions is correct, and why?

Answer 1

If you are simply looking for schemas that claim to deal with cases like yours, there is a website with hundreds of published schemas. Some of these pertain to storing transaction data concerning customers and suppliers. You can take one of these and adapt it.

http://www.databaseanswers.org/data_models/

If your question is about how to relate accounts to business contacts, read on.

Customers, Services, and Dealers are all sub classes of some super class that I'll call Contacts. There are two well known design patterns for modeling sub classes in database tables. And there is a technique called Shared primary Key that can be used with one of them to good advantage.

Take a look at the info and the questions grouped under these three tags:

single-table-inheritance class-table-inheritance shared-primary-key

If you use class table inheritance and shared primary key, you will end up with four tables pertaining to contacts: Contacts, Customers, Dealers, and Services. Every entry in Contacts will have a corresponding entry in one of the three subclass tables.

An FK in the accounts table, let's call it Accounts.ContactID will not only reference a row in Contacts, but also a row in whichever of Customers, Dealers, Services pertains to the case at hand.

This may work outwell for you. Alternatively, single table table inheritance works out well in some of the simpler cases. It depends on details about your data and your intended use of it.

Answer 2

You can make table Accounts with three fields with FK to Customers,Dealers and Services and it's will close problem. But also you can make three table for each type of entity with accounting data. You have the deal with multi-system case in system design. Each system solve the task. But for deсision you need make pros and con analyses about algorithm complexity, performance and other system requirements. For example one table will be more simple to code, but three table give more performance of sql database.