SQL · Intermediate

SQL: trustworthy customer reports

Handle missing relationships, NULL values and customer reports without counting mistakes.

Prerequisite: SQL for everyday data · 60 minutes of guided study

2 published lessons, from first principles to a small project.

What you’ll be able to do

Follow the numbered modules. Read the example, explain why it works, attempt the exercise, then compare your result with the supplied checks.

Setup: A modern browser. JavaScript, TypeScript, Python and SQLite exercises run here; project workshops state their additional setup.

Times estimate guided reading and practice. Projects and revision can take longer.

Find missing relationships safely with NOT EXISTS
Ask whether a related row exists instead of multiplying rows with a join.
25 min · Browser exercise →
Project · Report on customers with no orders
A useful report must define what zero activity means.
35 min · Browser exercise →