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Stop reading SQL theory. Start solving.

This book is 84 hand-picked SQL problems that take you from your first SELECT statement to genius-level analytical queries — the kind that show up in real technical interviews.

No theory chapters. No filler. Every single problem gives you a clear prompt, a sample input table, the exact expected output, a working solution, and a plain-English explanation of why it works — not just what to type.

The seven volumes rise one honest step at a time: Beginner → Easy-Medium → Medium → Medium-Hard → Hard → Expert → Genius. Volume 1 is single-table filtering and sorting. By Volume 7 you're computing medians without window functions, counting concurrent events, and finding the smallest missing positive integer — pure interview-grade challenges.

Every query in this book was tested against a real database before publishing. No broken code, no queries that only work in theory.

Who this is for

You already know the basics of SQL and want to get genuinely good at it. Whether you're preparing for a data or backend interview, leveling up from simple queries to window functions and CTEs, or just want deliberate practice instead of passive reading — this is your workbook.

How to use it

Solve each problem yourself first. Open any free SQL playground, recreate the table, and write your own query before reading the solution. The reading comes second; the typing comes first.

Note: examples use standard SQL. A few advanced solutions (window functions, PERCENTILE_CONT, recursive CTEs) target PostgreSQL-style engines; equivalents are explained where they differ.

146 pages · 7 volumes · 84 problems · one complete path from beginner to expert.

What's inside (you can add this as a bulleted section)

Volume 1 — Beginner: single-table filtering, sorting, basic conditions

Volume 2 — Easy-Medium: aggregation, GROUP BY, HAVING, CASE, NULL handling

Volume 3 — Medium: INNER/LEFT joins, subqueries, the classic NULL traps

Volume 4 — Medium-Hard: multi-table joins and CTEs

Volume 5 — Hard: window functions (ROW_NUMBER, RANK, running totals, medians)

Volume 6 — Expert: interview-grade problems — pivots, recursive CTEs, graph traversal, sargability

Volume 7 — Genius: everything at once — gaps-and-islands, concurrent events, hierarchies, the hardest patterns

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Kick off your book project, get started with GhostAI, get better at marketing, or spend the day doing all three! Free live workshops on Zoom. Saturday, June 27, 2026.

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