SQL Fundamentals

Twenty-five multiple-choice questions, one from each lesson of SQL for Beginners. Every one puts a real table and a real query in front of you and asks what comes back: which rows an INNER JOIN quietly drops, why comparing a column to NULL returns nothing at all, what COUNT(*) and COUNT(column) disagree about, what TRUNCATE resets that DELETE does not, and the order the clauses actually run in, which is not the order you write them.

It is not a syntax quiz. Nothing here can be answered by recognising a keyword. The later questions go as far as window functions, top-N-per-group, and why wrapping an indexed column in a function quietly costs you the index.

Six are straightforward, twelve take a minute of reading, and seven are hard.

Every learner sits the same twenty-five questions, so one score can be compared with another.

Anyone who writes SQL by pattern-matching against queries that worked before and wants to find out how much of it they actually understand. It suits developers, analysts, and anyone preparing for an interview where a query gets put on a whiteboard.

It assumes you have seen a SELECT and know what a table is. It does not assume you have tuned a query or designed a schema.