Relational Queries, 1974
SQL has outlived almost every language that was supposed to replace it. This era seeds real tables and lets you interrogate them with SELECT, WHERE, ORDER BY, GROUP BY and JOIN until the answers stop surprising you.
Code and data track · 6 missions · boss mission, no written exam · free, no signup. Everything below runs in the browser terminal on the SERVBG home page.
What you will do
- read rows from a table
SELECT * FROM users;SQL was born at IBM in 1974 (SEQUEL). You describe WHAT you want; the engine figures out how.
- filter rows with a condition
SELECT * FROM users WHERE city = 'Sofia';WHERE is a filter over rows. =, >, <, LIKE — the query narrows to exactly what matters.
- sort the result set
SELECT * FROM users ORDER BY age DESC;ORDER BY sorts on any column, ASC or DESC. The database does the heavy lifting for you.
- aggregate — count the rows
SELECT COUNT(*) FROM users;Aggregates (COUNT, SUM, AVG, MIN, MAX) collapse many rows into one answer.
- group, then aggregate per group
SELECT city, COUNT(*) FROM users GROUP BY city;GROUP BY buckets rows, then aggregates each bucket. "How many per city?" in one line.
- Boss missioncombine two tables on a key
SELECT name, total FROM users JOIN orders ON users.id = orders.user_id;JOIN is the heart of relational: relate rows across tables by a shared key. Normalise, then join back.
Certificate
This is one of the original eras, so it ends at the boss mission: there is no written exam and no certificate for it. Clearing the boss marks the era complete and banks the XP. The expansion tracks (networking, Cisco IOS, FortiOS, containers, Kubernetes, cloud, operations, defence, models and the nine graphics eras) are the ones that carry exams.