Database Query Logic vs Quarry

Database Query Logic is an independent study app for building confidence with query reasoning, SQL behavior, joins, filters, aggregation, NULL handling, subqueries, indexes, transactions, and edge cases. Designed for beginners, students, developers, analysts, and interview candidates, it turns 160 focused questions into repeatable practice across Fundamentals, Practical Skills, Common Pitfalls, and Advanced Concepts. - FSRS spaced-repetition intervals - Weak-point heatmap to spot gaps - Daily challenge for steady progress - Mock exams for timed review - Explanation included with every question - Offline practice for study anywhere - No account or login required Practice offline, no login required. Your study flow is built for private, independent preparation. Independent study app for Database Query Logic practice. Not affiliated with, endorsed by, or sponsored by any company, certification body, exam operator, or vendor. All trademarks belong to their respective owners.

Data interview practice that runs entirely on your device. Write real SQL and Python (pandas), get graded instantly, and see exactly why. NEW IN 1.2 • Today's problem: one problem a day, on Home and in a new widget for your Home Screen and Lock Screen. • Streaks and a daily goal: solve something every day and watch the streak grow. • An optional daily reminder, off unless you turn it on. • 20 new problems: A/B tests, attribution, quartiles, pivots, rate limiters and more. • Make it yours: six accent colours and four code editor colour schemes. • Quarry Pro: every Medium and Hard problem, a review queue that brings back the problems you found hard, and every future problem pack. WHAT'S INSIDE • 188 problems across three tracks: SQL, pandas and Python (algorithms and data structures). • Real execution, real grading. Your output is checked against the expected result, with no self-marking. • Company-style practice. Filter problems written in the style of the company you're interviewing at. • Hints and full solutions when you're stuck. • Difficulty levels from Easy to Hard, grouped by topic. • A free-form Playground for scratch SQL and Python. • Designed for iPhone, iPad and iPhone Duo. FREE AND PRO Every Easy problem, a sample of Medium ones, the daily problem, streaks, the widget and the Playground are free. Quarry Pro unlocks the other 119 problems, the review queue and every future pack. Quarry Pro is available monthly or yearly (auto-renewing), or as a one-time lifetime purchase. Payment is charged to your Apple Account. Subscriptions renew automatically unless cancelled at least 24 hours before the end of the current period; manage or cancel them in your Apple Account settings. PRIVATE BY DESIGN No accounts. No analytics. No ads. No tracking. Quarry collects nothing and works fully offline. Terms of Use: https://www.apple.com/legal/internet-services/itunes/dev/stdeula/ Privacy Policy: https://mayankgulaty.github.io/quarry-site/privacy.html Built by a working data engineer, for analysts, data engineers, data scientists and software engineers who want a quiet, fast place to actually practice.