SQL Query Logic vs Quarry

SQL Query Logic is an independent study app for learners who want to understand how SQL queries work, not just memorize syntax. It is built for beginners, students, analysts, developers, and interview candidates who need structured practice across fundamentals, practical skills, common pitfalls, and advanced concepts. Practice through 160 focused questions, each with a clear explanation so you can learn from every answer. - FSRS spaced-repetition intervals to review at the right time - Weak-point heatmap to show topics that need attention - Daily challenge for steady practice - Mock exams for timed review - Offline practice for commutes, travel, or quiet study - No login required Use it to review SELECT logic, joins, grouping, filtering, NULL behavior, subqueries, set operations, and reasoning patterns that often cause mistakes. Independent study app for SQL 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. Practice offline, no login required.

Data interview practice that runs entirely on your device. Write real SQL and Python (pandas), get graded instantly, and see exactly why. NEW IN 1.1 • Designed for iPhone Duo: question and editor side by side when open, a focused layout when closed, and it adapts as you fold. • A new native design for iPhone and iPad, in light and dark mode. • 60 new problems: a staff-level data engineering set (gaps and islands, sessionisation, slowly changing dimensions, funnels, retention) and company-style SQL sets. • Clearer results: instant correct / not quite feedback, expected vs. actual tables, and the query plan for your SQL. WHAT'S INSIDE • 168 problems across three tracks: 61 SQL, 22 pandas and 85 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. PRIVATE BY DESIGN No accounts. No analytics. No ads. No tracking. Quarry collects nothing and works fully offline. Built by a working data engineer, for analysts, data engineers, data scientists and software engineers who want a quiet, fast place to actually practice.