This is a basic database design question. I want a table (or multiple tables) defining relationships between customers. I want it so PrimaryCustomer can be linked to multiple SecondaryCustomers, and can have many SecondaryCustomers with the same relationship.
PrimaryCustomerID RelationshipID SecondaryCustomerID
1) If the primary key is {PrimaryCustomerID} then I can only have one linked customer of any kind.
2) If the primary key is {PrimaryCustomerID, RelationshipID}, then I can only have one linked customer for each relationship type.
3) If the primary key is {PrimaryCustomerID, RelationshipID, SecondaryCustomerID}, then I can have whatever I like, but having all columns as the primary key seems completely wrong.
What’s the right way to set things up?
Number 3 is the right way to go for this data model. Linking tables often have all the columns in a join as all they do is link to other tables.