Welcome to your interview.
The question is on your right: SQL Keys and Adding Columns. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
Explain primary keys, foreign keys, and how you would add a new column to an existing table.