Common one-to-many table for multiple entities

Question

Suppose I have two tables, Customer and Vendor. I want to have a common address table for customer and vendor addresses. Customers and Vendors can both have one to many ad

Answer 1

I'd say the missing piece of the puzzle is the "is a" relationship that is often overlooked in data modeling; this is distinct from the familiar "has a" relationship. An "is a" relationship is similar to an inheritance relationship in a object oriented design. To model this you'll need a base table that represents the common attributes of vendors and customers. For example, we could call the base table "Organizations":

Organizations       Vendors               Customers
--------------      ---------------------  ---------------------
OrganizationID(PK)  OrganizationID(FK/PK)  OrganizationID(FK/PK)
AddressID1(FK)
AddressID2(FK)

In this example Vendor "is a" organization, and Customer "is a" organization, whereas an organization "has a" address. The Organizations, Vendors, and Customers tables share a common key and a common key sequence enforced by referential integrity.