Practice SQL online — real PostgreSQL exercises.
Practice SQL online with 60+ graded PostgreSQL exercises across E-Commerce, Social Media, and Banking datasets. Write queries against live PostgreSQL tables — SELECT, JOINs, GROUP BY, window functions, CTEs — and get an instant performance score on every submission.
Unlike SQL sandboxes or static tutorial sites, every SQL practice problem runs against 50,000+ real rows. The Smart Debugger diagnoses exactly what went wrong without spoiling the answer. Interview-ready SQL skills, built query by query.
- Live PostgreSQL query execution — real databases, real data
- Smart Debugger with 41 diagnostic rules
- 60+ auto-graded SQL exercises across 3 datasets
- 28-topic structured learning curriculum
- E-Commerce, Social Media, and Banking datasets
- Easy, Medium, and Hard SQL practice problems
- Daily SQL puzzle with streak tracking
- Free to start — no installation required
Practice on three real-world datasets
Each dataset is a fully relational PostgreSQL schema with tens of thousands of rows, so your queries behave exactly as they would in production — not on three-row toy tables.
- E-Commerce — users, orders, order_items, and products. Ideal for INNER and LEFT JOINs, revenue aggregations, and customer-cohort analysis.
- Social Media — users, posts, follows, and likes. Great for self-joins, engagement metrics, and window-function ranking.
- Banking — accounts, transactions, and transfers. Built for running totals, balance reconciliation, and date-range filtering.
How grading works
Every submission runs against the live database and is graded on two axes: correctness (does your result set match the expected output exactly?) and efficiency (a performance score derived from the query plan). You get an instant verdict on each attempt — and when something is off, the Smart Debugger explains the cause without handing you the answer.
What you'll learn
The 28-topic curriculum moves from the fundamentals to the patterns interviewers actually ask about: SELECT and filtering, every JOIN type, GROUP BY and aggregates, subqueries and CTEs, window functions, and query optimization. Keep the SQL cheat sheet open while you work, and read the deep-dive guides on JOINs and window functions on the blog.
Frequently asked questions
Is it actually free?
Yes. All Easy challenges, the SQL Playground, the SQL Sandbox, all curriculum topics, and the Daily Puzzle are free forever. No credit card required.
What SQL dialect do you use?
PostgreSQL. The most commonly tested database in technical interviews and the most powerful open-source option for data work.
Do I need to install anything?
Nothing. Sign up, and you're writing SQL against a live database in under 30 seconds. No Docker, no local setup, no configuration.
Are these real interview questions?
The challenge patterns — JOINs, GROUP BY, window functions, CTEs — are exactly what appears in data analyst and backend engineer interviews. They're graded on correctness and efficiency, the same way a code submission is.