SQL Query Semantics vs Quarry

SQL Query Semantics is an independent study app for understanding how SQL queries really work. Use it to build confidence with relational logic, joins, grouping, null handling, predicates, subqueries, and result-set reasoning. Designed for students, developers, data analysts, and interview candidates, the app includes 160 focused practice questions across Fundamentals, Practical Skills, Common Pitfalls, and Advanced Concepts. Features: - FSRS spaced-repetition intervals for smarter review - Weak-point heatmap to spot topics that need work - Daily challenge for consistent practice - Mock exams for timed review - Explanations for every question - Offline practice with no login required Practice offline, no login required. Independent study app for SQL Query Semantics practice. Not affiliated with, endorsed by, or sponsored by any company, certification body, exam operator, or vendor. All trademarks belong to their respective owners.

Quarry is a focused, offline gym for data and coding interviews. 108 hand-picked problems across SQL, pandas, and Python — write real code, run it on your device, and get graded instantly. Everything runs on-device. The SQL and Python engines are built into the app, so there's no sign-up, no internet requirement, and nothing you write ever leaves your phone or iPad. Practice on a plane, on the subway, or anywhere. WHAT'S INSIDE • 108 problems across three tracks: SQL queries, pandas data wrangling, and Python algorithms & data structures. • Real execution, real grading. Your output is checked against the expected result — no self-marking. • Company tags. Filter problems by 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. • Universal app — designed for both iPhone and iPad. PRIVATE BY DESIGN No accounts. No analytics. No ads. No tracking. Quarry collects nothing and works fully offline. Whether you're prepping for a data analyst, data engineer, data scientist, or software role, Quarry gives you a quiet, fast place to actually practice.