Step 6 of 6 — Stretch

Grouping and aggregation — one answer per group

Ten questions, the first easy and the last hard. An explanation follows every answer — the ones you get wrong are the useful ones.

Answering needs an account

Reading needs no account — the chapter is open in full. But answering the ten questions, seeing the explanations and getting a result needs one.

Reading the chapter needs nothing — Grouping and aggregation — one answer per group is open in full.