CSE28 · CSE foundations & data structures

SQL Joins Detective

A school library lost track of books. Use SELECT, JOIN and GROUP BY on the library tables to find the answers.

📶 L200⏱ 30 min🧪 Live lab

🎯 You will learn to

Filter with WHERE
Join two tables
Group and count

🧪 Live environment

Runs entirely in your browser: nothing is installed, no real cloud account is used and your code is never sent to our server.

Loading the lab…

✅ Steps & checkpoints

Run the starter query
Answer case 1 with a JOIN
Answer case 2 with GROUP BY
Solve the LEFT JOIN case

🗺️ Library joins

Members and books meet in loans; INNER JOIN keeps matches, LEFT JOIN keeps every member, GROUP BY counts.

The 2D diagram shows the exact flow, ports and trust boundaries. The 3D scene is a concept view of the same parts; packets travel along the same arrows.

🤔 Think about it

When do you need a LEFT JOIN instead of an INNER JOIN?

Your answer (kept only on this device)

🛡️ Safety & cost

Simulations and in-browser runtimes only.

🧹 Cleanup

Nothing to clean up.

📚 Reference documents

SQL as understood by SQLite · SQLite
Introduction to Algorithms (6.006) · MIT OpenCourseWare
The Python Tutorial · Python
Linux man pages · man7.org

Official sources, checked on 5 Nov 2026. Cloud services change often; check the official page before relying on a feature. All references