Difference between one-to-one and one-to-many relationship in database

Question

This is probably a basic(dumb) question but when having a one-to-one relationship in a database the other table has a foreign key ID(in this example). And in a one-to-many relat

Answer 1

To enable one-to-one relationship you need to add unique constraint to foreign key. It is not possible to have two foreign keys for each table as it will be impossible to create records.