Sql quiz

Test your Sql knowledge with a free interactive quiz — 50 questions with answers and explanations. No signup needed to play.

What does SQL stand for, and what is it primarily used for?

1. What does SQL stand for, and what is it primarily used for?
2. ``` SELECT department, AVG(salary) FROM employees GROUP BY department; ``` What does this query return?
3. What does `SELECT * FROM t` do?
4. What does `LEFT JOIN orders o ON o.user_id = u.id` return for users with no orders?
5. Which clause filters AGGREGATED groups, not individual rows?
6. What is the practical difference between `DELETE FROM t` and `TRUNCATE TABLE t`?
7. What does a `PRIMARY KEY` constraint guarantee?
8. How do you limit a result to the first 10 rows in standard SQL (and PostgreSQL/MySQL/SQLite)?
9. What does `INNER JOIN` return?
10. What is the difference between `COUNT(*)` and `COUNT(col)`?
11. ``` SELECT u.name, o.id FROM users u JOIN orders o ON o.user_id = u.id; ``` Which type of join is this (implicit / explicit)?
12. What does a `UNIQUE` constraint provide that `PRIMARY KEY` does not (and vice versa)?

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