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85 hands-on challenges on four real databases. Write a query, run it, and get feedback that tells you exactly what's off. No signup, no setup.

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79 bite-size lessons
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department_report.sql employees

Challenge

Which departments have more than 5 employees? Return department_name and total_employees, biggest first.

Challenges: 85
Lessons: 79
Databases: 4
Tables to query: 29
Accounts needed: 0

Instant feedback

Wrong answers that teach.

Most practice sites stop at "incorrect". Query Dojo compares your result with the expected one and tells you what's different: a missing alias, extra rows, the wrong column order, a filter that let too much through.

Every query runs on a real SQLite engine inside your browser, so results come back in milliseconds, even offline.

Attempt 1 Not quite

SELECT d.name AS department_name, COUNT(*)
FROM employees e
JOIN departments d ON e.department_id = d.id
GROUP BY d.name
HAVING COUNT(*) > 5;

Your column 'COUNT(*)' should be named 'total_employees' - add AS total_employees.

Attempt 2 Not quite

SELECT d.name AS department_name, COUNT(*) AS total_employees
FROM employees e
JOIN departments d ON e.department_id = d.id
GROUP BY d.name;

Expected 3 rows, you returned 5. 2 rows shouldn't be there.

Attempt 3 Solved · +10

SELECT d.name AS department_name, COUNT(*) AS total_employees
FROM employees e
JOIN departments d ON e.department_id = d.id
GROUP BY d.name
HAVING COUNT(*) > 5
ORDER BY total_employees DESC;

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Daily practice

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A new free challenge every day, the same one for everybody. Solve it for a bonus and keep your streak alive.

Today's challenge Start a streak today

Group Albums by Decade

The music team wants to analyze catalog distribution across decades.

Easy Aggregation music

Solve it for +25 points (10 + 15 daily bonus)

Train by topic

12 SELECT & filtering WHERE, ORDER BY, LIKE, CASE, dates and strings 23 JOINs Inner, left and self joins across related tables 38 Aggregation GROUP BY, HAVING, COUNT, SUM, AVG 27 Subqueries Nested SELECTs, IN, EXISTS and correlated queries 19 Window functions ROW_NUMBER, RANK, LAG, running totals 22 CTEs WITH clauses and recursive queries 16 Writes & indexes INSERT, UPDATE, DELETE, CREATE INDEX 4 Transactions BEGIN, COMMIT, ROLLBACK, SAVEPOINT

transaction.sql The Atomic Stock Transfer

BEGIN;
UPDATE product_inventory SET current_stock = current_stock - 50 WHERE product_id = 1;
UPDATE product_inventory SET current_stock = current_stock + 50 WHERE product_id = 3;
COMMIT;

Forget the COMMIT and everything rolls back

Beyond SELECT

Practice the queries that change data.

INSERT, UPDATE, DELETE, indexes and real transactions run on a private copy of the database, so nothing you write can break it. Then we check the table, not just your syntax.

Try a transaction challenge

Real data