Databases · Middle · Question 67 of 75

What does `SELECT DISTINCT ON (user_id) * FROM orders ORDER BY user_id, created_at DESC` return?

1Only users with exactly one order
✓Correct answer: One row per user: the first by the given order, here the latest order
3All orders without duplicates

Explanation

DISTINCT ON is a PostgreSQL extension for 'latest per group'. The ORDER BY must start with the DISTINCT ON columns.

Further reading

PostgreSQL: SELECT ↗

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