SQL for Beginners: Ask Your Data Straight Questions

Read, change and combine data in PostgreSQL without guessing what a query does. This is for people who have never written SQL, or who copy queries without knowing why they work. You will set up PostgreSQL 18, ask a small shop database for rows, change data safely, summarise it, and join tables without losing or doubling rows. If you skip the NULL and join checks, your queries will return answers that look right and are not.