Independent practice · SQLite

Count unique customers by stage

Your task

Target: 70/100. Suggested active time: 10 minutes. You can keep working after that.

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Use COUNT(DISTINCT customer_id).

View the scoring standard

Accuracy checks the values. Coverage checks the requested output. Time is recorded separately and never changes your score.

columns: 20 points

rows: 80 points

Tables and practice data

order_id	customer_id	status	amount	region	ordered_at
1	1	paid	120	East	2026-09-01
2	2	pending	140	West	2026-09-02
3	1	paid	100	East	2026-09-03
4	3	paid	180	West	2026-09-03
5	99	paid	80	East	2026-09-04
6	NULL	cancelled	0	NULL	2026-09-04
7	2	paid	120	West	2026-09-05
8	4	paid	30	North	2026-09-06

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SQL query

Import answer

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SELECT stage, COUNT(DISTINCT customer_id) AS customers FROM events GROUP BY stage

The repeated visit from customer 1 must count once.