Databases · Junior · Question 22 of 75

What does a `LEFT JOIN` return?

SELECT u.name, o.id
FROM users u
LEFT JOIN orders o ON o.user_id = u.id;

1Only orders that have no user
2Only users who have orders
✓Correct answer: Every user; for users without orders the order columns are NULL

Explanation

A LEFT JOIN keeps all rows from the left table. RIGHT JOIN does the same for the right table, and FULL JOIN keeps unmatched rows from both.

Further reading

PostgreSQL: Joins between tables ↗

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