Developer C · Backend

Database and API: data modelling, SQL, indexes and transactions, plus API design, auth, validation, errors, versioning and operations.

Verified level

CWorkingMedium confidence

Reviewed 2 months ago by Developer B.

Self assessment

BProficient

Above the verified level — waiting on an owner review.

Target

Target met.

Checklist

6/29

1 item flagged for review.

Assigned to reach C by 13 Oct 2026 — Work through the SQL block, then present what you learned.

Learning log (4)

NotePrimary key vs unique constraint29 Sept 2026

A table has one primary key; unique constraints can be many and allow a NULL depending on the engine.

Code exampleLEFT JOIN that keeps orphan rows29 Sept 2026

SELECT c.id, o.total
FROM customer c
LEFT JOIN "order" o ON o.customer_id = c.id
WHERE o.id IS NULL;

LinkUse The Index, Luke29 Sept 2026
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Recommended by the database owner.
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https://use-the-index-luke.com
Open questionWhen is a composite index worse than two single ones?29 Sept 2026
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Ask in the next review session.
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