Window Functions vs GROUP BY

Context

In product analytics at Splice, you often need both summarized metrics and row-level context. Interviewers ask this question to check whether you understand when SQL should collapse rows versus when it should preserve them.

Core question

Explain the difference between a window function and a GROUP BY in SQL. In your answer, cover:

1. How each changes the shape of the result set
2. What kinds of analysis each is best suited for
3. When you would use one instead of the other in a Splice example, such as analyzing Studio sessions, sample downloads, or subscription activity
4. Whether they can be used together in the same query

Scope guidance

Keep the answer practical rather than purely theoretical. The interviewer is looking for a clear explanation of behavior, a few concrete examples, and awareness of common mistakes such as using GROUP BY when you still need row-level detail.