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Return the latest staged row per non-null customer_id with customer_id, email, tier, is_deleted, updated_at, and batch_id.
Result columns · in this order
customer_id | Business key for the customer; one row is intentionally NULL for key validation practice. |
email | Customer email from the source system. |
tier | Customer tier attribute. |
is_deleted | 1 when the source row is an explicit tombstone. |
updated_at | Source update timestamp. |
batch_id | Ingestion batch identifier used as a deterministic tie-breaker. |
How to approach it
Filter null keys, rank each customer, then keep the newest row.
Sample input
| customer_id | tier | is_deleted | updated_at | batch_id | |
|---|---|---|---|---|---|
| 101 | ana@example.com | gold | 0 | 2026-03-05 10:00:00 | 7001 |
| 102 | ben@example.com | silver | 0 | 2026-03-05 11:00:00 | 7001 |
| 103 | cy@example.com | bronze | 1 | 2026-03-05 12:00:00 | 7001 |
| 104 | dee-old@example.com | gold | 0 | 2026-03-05 09:00:00 | 7000 |
| 104 | dee@example.com | platinum | 0 | 2026-03-05 12:30:00 | 7001 |
| 105 | eli@example.com | bronze | 0 | 2026-03-05 08:00:00 | 7001 |
| null | ghost@example.com | silver | 0 | 2026-03-05 13:00:00 | 7001 |
| 106 | fay@example.com | silver | 0 | 2026-03-04 23:30:00 | 6999 |
8 rows — all rows shown.
Expected output
| customer_id | tier | is_deleted | updated_at | batch_id | |
|---|---|---|---|---|---|
| 101 | ana@example.com | gold | 0 | 2026-03-05 10:00:00 | 7001 |
| 102 | ben@example.com | silver | 0 | 2026-03-05 11:00:00 | 7001 |
| 103 | cy@example.com | bronze | 1 | 2026-03-05 12:00:00 | 7001 |
| 104 | dee@example.com | platinum | 0 | 2026-03-05 12:30:00 | 7001 |
| 105 | eli@example.com | bronze | 0 | 2026-03-05 08:00:00 | 7001 |
| 106 | fay@example.com | silver | 0 | 2026-03-04 23:30:00 | 6999 |
6 rows — all rows shown.
Constraints
Use ROW_NUMBER partitioned by customer_id ordered by updated_at DESC, batch_id DESC. Exclude NULL customer_id rows, keep row_num = 1, and order by customer_id.
Expected skills
Staging hygiene, deterministic tie-breaking, and one-row-per-key merge sources.
Submit for review to find out what your query gets right, what it gets wrong, and how it compares with the best working query for this exercise.
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