SQL for beginners: explore a PostgreSQL database

Mama Ngo has run her shop in Nkoldongo, Yaoundé, for twenty years. Groceries, soap, sardines, Maggi cubes. And a notebook, where everything was written down. In the spring, her nephew set up a till on an old laptop; since then, everything is entered and nobody knows anything any more. "The notebook, I opened it and I could see. Here, I see a black screen." This workshop is a first encounter with a database, and it is designed for someone who has never opened one. You will not write a line of SQL and you will not open any terminal: you work in a web interface, from a link, and you look. Learning the command line and the idea of a table at the same time means stacking two difficulties that have nothing to do with each other. The guide is not read, it is practised. In six places it asks you to answer before carrying on, and the commented answer waits under a ribbon you only pull once you have decided. Looking for an answer, even getting it wrong, fixes an idea far better than reading it. In an hour and a quarter, you will know what a table, a column, a row and a type are; why a price stored as text breaks the calculations six months later; and why an empty cell and a zero do not mean the same thing, the confusion that will make two thirds of someone else's sales disappear, later in the path. SQL is the most requested technical skill for entry-level jobs, and the one most independent of the employer's technical choices: it is just as useful in an SME running an ERP as for reconciling a mobile money account. This is where you start.