MySQL is the open-source relational database that powers WordPress, Facebook's early systems, and millions of other websites. When an app needs to store users, posts, orders, or anything else permanently, MySQL is often where that data lives. If you want to build a real web app — or you want a database skill that appears on almost every backend job listing — MySQL is one of the best places to start.

How does MySQL work? You store data in tables, like spreadsheets: each table has columns, like name and email, and each row is one record, like one user. You talk to MySQL with SQL, the standard database language: SELECT reads data, INSERT adds it, UPDATE changes it, and DELETE removes it. You can join tables together — for example, joining users to their orders — so you can answer questions that span your whole dataset.…