A primary key must carry a value. Does this value have to be unique? If so$,$ where does need to be unique?

It must be unique in its table, such that no two rows can have the same primary key

It must be unique within the row, such that no columns can have the same value as the primary ke

It must be unique throughout the entire database, such that no two primary key values can be the same throughout all tables in the database, regardless of the associations between tables

The primary key does not need to be unique, particularly when it is carrying a copy of another tabl primary key