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This problem is paper-only - see explanation for the canonical SQL solution.
Given Customers(id, total_spend), bucket customers into quartiles by total_spend ascending using NTILE(4). Lower spend gets quartile 1; higher spend gets quartile 4.
Tiebreak by id ascending. Return [{ id, total_spend, quartile }] sorted by quartile ascending, total_spend ascending, id ascending.
For the auto-grader: implement assignQuartiles(customers).
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, total_spend,
NTILE(4) OVER (ORDER BY total_spend ASC, id ASC) AS quartile
FROM Customers
ORDER BY quartile, total_spend, id;
```
NTILE bucketing rule: with `n` rows split into `k` buckets, the first `n mod k` buckets get `ceil(n/k)` rows; the remaining buckets get `floor(n/k)` rows. Example: 10 rows / 4 buckets -> sizes 3, 3, 2, 2.
When to prefer percentiles instead: `NTILE` is positional, not value-based. Two customers with identical spend can land in different buckets. If you need value-based bucketing, use `PERCENT_RANK` or `CUME_DIST` with explicit thresholds.
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.