SQL Quest › SQL Interview Questions › Subqueries & CTEs
EXISTS vs IN: Departments with Top Performers
Google's performance review system flags departments that have at least one top performer (performance_rating >= 4.5) for leadership bench-strength reports. Write it with EXISTS (correlated subquery). Show department and dept_avg_rating (average performance_rating, 2 dec). Sort by dept_avg_rating DESC. EXISTS vs IN is a Google-favorite interview because of the optimizer question underneath: EXISTS short-circuits on first match (fast when your subquery is big), while IN materializes the entire subquery set. At Google's scale, getting this right is the difference between a query that runs in 2 seconds vs 2 minutes on a billion-row table.
Solve it in the browser editor →
Runs on SQLite in your browser, graded against the expected result, no signup. A wrong answer gets a diagnosis, not just "incorrect".
Schema
employees
| emp_id | name | department | position | salary | hire_date | manager_id | performance_rating |
|---|---|---|---|---|---|---|---|
| 1 | Alice Johnson | Engineering | Senior Developer | 95000 | 2019-03-15 | 5 | 4.5 |
| 2 | Bob Smith | Engineering | Developer | 75000 | 2020-06-01 | 1 | 3.8 |
| 3 | Carol Williams | Marketing | Marketing Manager | 85000 | 2018-09-20 | NULL | 4.2 |
Expected output: Engineering appears with its dept average
Hint
Concepts
SELECT EXISTS Subquery Correlated Subquery GROUP BY EXISTS / Subquery
Practise the topic: SQL practice questions · CTE practice · GROUP BY exercises
In these company practice sets
Amazon · Google · Meta · Snowflake
A SQL Quest challenge matched to patterns reported for these companies — not a question any of them has published.
Related questions
Where would this cost you points in an interview?
Ten questions, no signup: a Skillmap across nine SQL skills and the one to fix first.
Take the readiness test