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SQL Mastery Series

A Problem-Solving Workbook — 84 Solved SQL Challenges from Beginner to Interview-Ready

This book is 100% completeLast updated on 2026-07-02
Hatem M.

84 hand-picked SQL problems, fully solved and explained — from your first SELECT to interview-ready queries. Seven volumes of pure practice: a problem, the data, the answer, and why it works. No theory chapters, no filler, every query tested against a real database. Solve first, read second.

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About

About

About the Book

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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Author

About the Author

Hatem M.

Hatem M. is a programmer and technical author whose work focuses on modern C++, large language models, and AI systems.

His books combine first-principles explanations with complete implementations and reproducible experiments. They include C++ Algorithmic Mastery, an eight-volume series on algorithms and problem solving; Build an LLM Inference Engine in C++, which constructs a GPT-style inference engine from scratch; LLM Quantization: From the Bits Up, which develops the theory and practice of neural network quantization from the bit level upward; and C++ Autopsy, a forensic investigation of ten subtle C++ bugs that compiled successfully, ran correctly, and still produced the wrong answers.

Contents

Table of Contents

What's Inside

7 Volumes · 84 Problems · One Complete Path

Volume 1 — Beginner

Single-table filtering, sorting, and basic conditions. Your foundation: SELECT, WHERE, ORDER BY, and reading a query the way the database does.

Volume 2 — Easy-Medium

Aggregation and grouping: GROUP BY, HAVING, CASE, and the NULL traps that quietly break beginner queries.

Volume 3 — Medium

Joins and subqueries enter the picture: INNER JOIN, LEFT JOIN, IN, EXISTS, and the recurring NULL pitfalls hiding inside them.

Volume 4 — Medium-Hard

Multi-table joins and Common Table Expressions (CTEs). Breaking a hard question into readable, composable steps.

Volume 5 — Hard

Window functions: ROW_NUMBER, RANK, DENSE_RANK, running totals, and medians — the tools that separate casual users from strong ones.

Volume 6 — Expert

Interview-grade problems: pivoting, recursive CTEs, graph traversal, cohort retention, and query sargability — where correctness alone is no longer enough.

Volume 7 — Genius

Everything at once: medians without window functions, gaps-and-islands, concurrent-event counting, hierarchies, and the smallest missing positive integer. The hardest patterns, one final time.

Every problem includes a prompt, sample input data, the expected output, a working solution, and a plain-English explanation. Every query tested against a real database before publishing.

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