SQL is everywhere these days. Whether you're learning backend development [https://www.boot.dev/], data engineering, DevOps, or data science, SQL is a skill you'll want in your toolbelt. This a free and open text-based handbook. If you want to get started, just scroll down and start reading. That said, there are two

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The SQL Handbook is a free and open text-based handbook for Web Developers. Try the interactive version of this SQL course on Boot.dev, complete with coding challenges and projects. Watch the video walkthrough of this course on FreeCodeCamp's YouTube channel.

The SQL Handbook – A Free Course for Web Developers

Chapter 6: How to Structure Return Data in SQL

Chapter 7: How to Perform Aggregations in SQL