With these it helps One-to-one isn't well represented as a first-class relationship type in standard SQL. Much like many-to-many, which is achieved using a connector table and two one-to-many relationships, there's no true "one to one" in SQL. There are a couple of options:
may help you . There are a couple different ways to address this. The question really is about how they get loaded. Do you need to do a check to see if they exist first? This check can have a big hit on performance if done needlessly. The most performant way to accomplish this is through a separate step assuming you can just blindly insert them in that earlier step.