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This problem is paper-only - see explanation for the canonical SQL solution.
Given Orders(id, customer_id, order_date, total), return each row plus a running_total column that is the cumulative spend for that customer up to and including the current row, ordered by (order_date, id) within each customer. Sort the output by customer_id ascending, order_date ascending, id ascending.
For the auto-grader: return [{ id, customer_id, order_date, total, running_total }].
A medium sql problem, graded against 6 test cases (4 of them hidden).
Query-writing problems - joins, aggregation, window functions, and query tuning.
Reach for it when you see: A schema and a question about the data rather than a function signature.
More SQL problems →```sql
SELECT id, customer_id, order_date, total,
SUM(total) OVER (
PARTITION BY customer_id
ORDER BY order_date, id
ROWS UNBOUNDED PRECEDING
) AS running_total
FROM Orders
ORDER BY customer_id, order_date, id;
```
ROWS vs RANGE:
- `ROWS` is positional - exactly N rows back / forward.
- `RANGE` is value-based - includes peers (rows with the same ORDER BY value).
For a running total this difference matters when ORDER BY has ties: `RANGE` will sum all peer rows together, `ROWS` won't. The interviewer might ask "what happens with two orders on the same date?" - know the answer.
The full reference solution in every supported language stays in the editor above - reveal it there once you have had a real attempt.
Read off this problem's own test suite, so these are the cases a submission actually has to survive.
These apply to the pattern as a whole, not just this problem.