Orders per User in One Report

#994

The report currently recounts orders separately for every user, which scales poorly on larger data. Rewrite it as one set-based calculation: every user must remain in the result, even with no orders. Return id and orders_count, sorted by id.

Original query

SELECT u.id, (SELECT COUNT(*) FROM orders o WHERE o.user_id = u.id) AS orders_count FROM users u ORDER BY u.id

Voorbeeld van verwachte uitvoer

Zo ziet een correct antwoord eruit — het aantal rijen is op zichzelf staand en hoeft niet overeen te komen met de schematabellen.

id	orders_count
1	2
2	2
3	1

Je queryresultaat verschijnt hier