Every SQL skill you'll build later rests on a handful of core ideas. This module covers how relational databases organize information into tables made of rows and columns, why each column has a data type, and how primary keys and foreign keys connect one table to another.
You'll also get a working database set up on your own machine and write your first statements against it — creating a table, inserting a few rows, and reading them back with SELECT — so everything in the following modules is something you can run and experiment with yourself.
Work through the lessons in order, then continue on to Querying & Filtering.
Web Dev Simplified's fast, practical introduction to SQL: what a relational database is, how tables and data types work, and the core statements for creating, reading, and changing data.
Mike Dane's freeCodeCamp course walks through installing MySQL, designing tables, working with keys, and the essential CRUD operations, joins, nested queries, triggers, and ER diagrams — a thorough foundation you can follow along with.
Programming with Mosh's step-by-step MySQL course: setting up a database, writing your first queries, and building confidence with the core SQL statements you'll use throughout the rest of the course.