Most SQL courses warn you about joins. In our data, joins were not the hard part. The first lesson was. We make SQLMaxx Learn, a free SQL course with 66 lessons and 615 practice problems. You write each query, and PostgreSQL runs it in your browser. From August 19 to October 25, 2026, 99 learners with accounts sent 13,105 graded answers. Here is what we found. Also: Our SQL course, SQLMaxx Learn , is completely free, and you do not need an account to start. How we counted, ...