Question

I’m designing a database that will hold contracts and warranties. A warranty can link to a contract but doesn’t depend on a contract to exist. How can I define the relationship between the 2?

Answer 1

Assuming that a contract must link to exactly one warranty, I’d have 2 tables:

Contract
  ContractId  (Primary key)
  WarrantyId  (foreign key to Warranty'Warranty_Id
  ...
  ...

Warranty
  Warranty_Id  (Primary key)
  ...
  ...

If, on the other hand, a contract can link to none, or more than 1 warranty, then I’d have a junction table instead:

Contract
  ContractId  (Primary key)
  ...
  ...

Warranty
  Warranty_Id  (Primary key)
  ...
  ...

ContractWarranty
  ContractId  (Primary key) (Foreign key to Contract table)
  Warranty_Id (Primary key) (Foreign key to Warranty table)