Start

How the course works

5 min

What you'll learn

what SQL really is: you phrase a question about the data, and the database engine works out the search route on its own
how to tell apart the four kinds of lesson block — theory, live SQL, question and practice — and use each one for what it’s good at
when a lesson counts as done: reach the end and answer the questions

This course is built on PostgreSQL — one of the most in-demand open-source databases. That’s a deliberate choice, not a limitation: the core SQL constructs carry over to MySQL, SQL Server and SQLite for the most part. Every place where the dialects diverge is flagged with a purple callout like this one; at the end of Module 6 you’ll find a cheat sheet mapping the dialects to each other.

What you need to start: no programming background required — just a browser.

Prologue — "The Signal"

The year is 2184. The orbital archive station Vault-9 is the last surviving node of the Academy of Archivistics. Today is your first day of practical training: a dim corridor, amber holopanels, the steady hum of server racks. From a speaker comes a voice that sounds a lot like purring.

QUERY: Cadet. I’m module S.Q.L.: the full name is a mouthful, but the job is simple — I turn your questions into queries against the data. A request in the language of the archives is called a query, so everyone just calls me QUERY. Your timing is good: overnight the station picked up something out of a dead sector of the Net.

The signal repeats with the stubbornness of a lighthouse. Inside is something no one has come across since the Great Severance: an untouched database from old Earth. A PostgreSQL of the online shop "Kotomarket", from 2024 — buyers, products, orders, events — a whole life, deliberately preserved by someone. To read it, you need the language of the archives: SQL. And that’s what you’ll be taught here — not just from lecture notes.

A cadet in an orbital station corridor stares at a holopanel showing a repeating signal from a dead sector of the Net — First watch aboard Vault-9: the station picks up a signal, and inside it sits an untouched 2024 database.

How your watch works

This isn’t the kind of course where you read a page and close the tab. Here you see a short idea, run a live SQL query and immediately test it against the data of the online shop "Kotomarket".

Every lesson is built like a short working shift for a data archivist:

theory — you work out why a new construct is needed;
live SQL — you run an example, then tweak it on the spot and check the result;
question — a quick check that the idea actually landed;
practice — you lock in the skill on tasks in the trainer.

A lesson counts as done once you’ve reached the end and answered the questions. That’s how SQL stops being a pile of words and becomes a working tool — and every module you finish raises your clearance level for the archive.

SQL (Structured Query Language) is the language of queries to databases. Aboard Vault-9 they call it the language of the archives, but the essence hasn’t changed since 2024: you phrase a question — which products, orders or events from "Kotomarket" you need — and the database engine picks the search route on its own.

While you were getting your bearings, QUERY loaded the whole . At the very end of the file, below the last row of data, sits a comment left by a human: "For the one who knows how to ask. Start with SELECT. — K." Who K. is, the archives won’t say. What SELECT is — you’ll find out right now.