Lets try this scenario:
I will have one master table in my database, lets call it "customers". Each
customer has several invoices which will be stored in an "invoices" table.
Either of the tables may exist or may not exist, or both may exist. I can determine that easily enough with GetSchema and return all of the "TABLE" items.

I want to link the "customer" table and the "invoices" table so that each customer can have many invoices and so that I can retrieve them as needed using a standard query. I believe the relationship is called "one to many"

If I use Access, I can link the tables using the relationships tool, but my users will not have Access, and as such must interact with the interface I am building.

I have searched for a couple of weeks and have found nothing which relates to doing this programmatically, even if it was written in another programming language it would be helpful. I think I just need the correct query string syntax.

I'd appreciate any guidance.