Welcome to your interview.
The question is on your right: Optimizing GROUP BY Aggregations. 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.
How do you approach data aggregation using GROUP BY for massive datasets to minimize processing time?