This page outlines some of the fundamental properties of SQL programming that you need to know as you start learning SQL. For example, SQL is a declarative language, meaning that you tell it what you want and not how to compute it. Also SQL syntax is not well-ordered, meaning that the order in which SQL statements are evaluated is not the same as the order that they appear.
Lukas Eder. 10 Easy Steps to a Complete Understanding of SQL. Created March 17, 2016. Available in html format.
You can find an earlier version of this page on my blog.