A database administrator creates a new database and assigns the primary key.

A relational database uses tables consisting of rows and columns where a primary key uniquely identifies each row (record). As stated in the CompTIA ITF+ FC0-U71 Official Study Guide:

"Relational databases store data in tables consisting of rows and columns. Each table has a primary key, which uniquely identifies each record."

"Document and key/value databases are types of NoSQL databases and do not use primary keys in the same structured tabular format."

Non-structured databases (like object storage or big data repositories) do not enforce primary keys.