Independent practice · SQLite

Produce canonical refund records

Practice dataset

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Your task

Return refund_id, order_id, amount, status, booked_at sorted by refund_id.
Keep one exact record per nonconflicting refund_id. Exclude all variants of conflicting keys. Do not apply status/date filters yet.

Pass every output check to complete this task. Suggested active time: 10 minutes. You can keep working after that.

Required output

Return exactly these columns in this order.

refund_idstring
order_idnumber
amountnumber
statusstring
booked_atstring

Expected output: 9 rows. Keep the requested row order.

Values, data types and the number of copies of each row must match. A missing value is distinct from zero and from an empty string.

Preserve SQL NULL unless the task explicitly gives a replacement rule. Check JOINs for extra copies of rows.

Reconciliation checks

Every requested business key appears once.
Preserve SQL NULL and exact output column names.

Need a next step?

Hint 1: where to start

Find the conflicting keys first.

Hint 2: build the method

Exclude all rows with those keys, then SELECT DISTINCT.

Hint 3: check your work

NOT EXISTS can express “no disagreeing record shares this key.”

How your work is checked

Every output check must pass. The score shows how much matched and helps you find mistakes; completion comes from passing all checks. Active time is recorded separately.

Passing records a correct practice output on this device. It is not a professional certification.

Source materials

21 original source records.

Data dictionary

orders.order_id integer: Unique sale key; an unmatched refund must not create a sale.
orders.region text: Sales reporting region.
orders.status text: Only paid sales qualify.
orders.amount integer: Sale value in cents; includes zero.
orders.ordered_at text: ISO sale date; select the half-open reporting month.
refunds.refund_id text: Business key. Collapse exact repeats; exclude all conflicting variants.
refunds.order_id integer: May be orphaned or refer to a sale outside the cohort.
refunds.amount integer: Positive refunded cents; multiple distinct refunds may belong to one order.
refunds.status text: Only posted refunds reduce revenue.
refunds.booked_at text: ISO booking date; apply the same half-open reporting month.

View database setup and records

CREATE TABLE orders (order_id INTEGER, region TEXT, status TEXT, amount INTEGER, ordered_at TEXT);
INSERT INTO orders VALUES
(4000,'East','pending',1000,'2026-09-01'),
(4001,'West','paid',1125,'2026-10-01'),
(4002,'North','paid',1250,'2026-09-01'),
(4003,'East','paid',1375,'2026-09-04'),
(4004,'West','paid',0,'2026-09-05'),
(4005,'North','paid',1625,'2026-09-06'),
(4006,'East','paid',1750,'2026-09-07'),
(4007,'West','pending',1875,'2026-09-08');
CREATE TABLE refunds (refund_id TEXT, order_id INTEGER, amount INTEGER, status TEXT, booked_at TEXT);
INSERT INTO refunds VALUES
('R4000',4002,100,'requested','2026-09-01'),
('R4001',4003,110,'posted','2026-09-02'),
('R4002',4004,120,'posted','2026-09-03'),
('R4003',4005,130,'posted','2026-09-04'),
('R4004',4006,140,'posted','2026-09-05'),
('R4005',4007,150,'posted','2026-09-06'),
('PART-4000',4003,200,'posted','2026-09-01'),
('OVER-4000',4005,9999,'posted','2026-09-01'),
('ORPH-4000',4999,250,'posted','2026-09-01'),
('END-4000',4006,800,'posted','2026-10-01'),
('R4001',4003,110,'posted','2026-09-02'),
('R4001',4003,110,'posted','2026-09-02'),
('R4002',4004,121,'posted','2026-09-03');

Your work

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SQL query

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Show the reference answer

WITH clean_refunds AS (
 SELECT DISTINCT r.* FROM refunds r WHERE NOT EXISTS (
  SELECT 1 FROM refunds x WHERE x.refund_id=r.refund_id AND
  (x.order_id<>r.order_id OR x.amount<>r.amount OR x.status<>r.status OR x.booked_at<>r.booked_at)
 )
) SELECT refund_id,order_id,amount,status,booked_at FROM clean_refunds ORDER BY refund_id

First resolve identity over the entire source; only then apply accounting eligibility.