SQL Interview Questions in 14 Days with Python 3.11

Fourteen days of drills on the SQL a technical interview actually asks for, run through nothing but Python's own standard library.

This is a drill manual, not a narrative course. Every listing was executed for real against a small SQLite database built up across the fourteen days, and every printed output block, including every EXPLAIN QUERY PLAN, is a paste from that run. Each chapter states a rule in as few words as it can, shows the rule working in a short numbered example with its captured output, and hands it straight back as problems. The vehicle is hiredb, one job-application database with four tables: applications, companies, contacts and a status-history log.

Only Python 3.11 or later is required. sqlite3 ships in the standard library, so there is no server to install, no account to create, and no driver to configure. Every listing runs unchanged on Windows, macOS and Linux.

The first week covers the ground a screen opens with: the table and the first query, SELECT and WHERE, every join type, GROUP BY and aggregate traps, subqueries and CTEs, window functions, and NULL and three-valued logic. The second week covers what separates a pass from a strong pass: indexes, reading a query plan, transactions and isolation, normalisation and schema design, calling SQL safely from Python, one full take-home task, and a closing chapter of forty timed questions, each worked and its own plan read.

The findings are reported as they came out. A missing index turns a two-hundred-thousand-row filter from fourteen milliseconds into one tenth of one. A naive pay comparison shows remote roles earning nineteen points more than onsite ones, and the gap nearly disappears once role is held constant.

Your 14-Day Path

• 1. THE TABLE, THE ROW AND THE QUERY


• 2. SELECT, WHERE AND THE FIRST QUESTIONS


• 3. JOINS: INNER, LEFT AND THE ONE THAT LOSES ROWS


• 4. GROUP BY, HAVING AND AGGREGATE TRAPS


• 5. SUBQUERIES, CTEs AND READABLE SQL


• 6. WINDOW FUNCTIONS


• 7. NULL AND THREE-VALUED LOGIC


• 8. INDEXES AND WHY YOUR QUERY IS SLOW


• 9. READING A QUERY PLAN


• 10. TRANSACTIONS AND ISOLATION


• 11. NORMALISATION AND SCHEMA DESIGN


• 12. SQL FROM PYTHON


• 13. THE TAKE-HOME DATA TASK


• 14. THE LIVE SQL SCREEN

Who It's For

Job seekers preparing a technical screen or a take-home assignment. Students learning SQL through Python's own standard library. Working developers whose SQL has stayed at a beginner's level for years. Anyone who wants every answer checked against a real database, not memorized.

284 worked examples. 286 figures. 650 numbered problems. 392 pages. Built and measured against Python 3.11 and SQLite 3.38.

You need only Python and about an hour a day. Start Day 1.