Not online, but SQL Antipatterns is the book that had the largest impact on my thinking: https://www.amazon.com/SQL-Antipatterns-Programming-Pragmatic-Programm

Not online, but SQL Antipatterns is the book that had the largest impact on my thinking: https://www.amazon.com/SQL-Antipatterns-Programming-Pragmatic-Programmers/dp/1934356557/ref=sr_1_1?ie=UTF8&qid=1484685482&sr=8-1&keywords=sql+antipatterns https://www.amazon.com/SQL-Antipatterns-Programming-Pragmati... But as you said, you haven't actively learned SQL, so probably need to find some free data sets to work with. You can probably start with Data is Plural. That will, at least, give you some raw data sets so you can get started on learning how to build up a database from unorganized data first: https://tinyletter.com/data-is-plural https://tinyletter.com/data-is-plural Edit to add: First and foremost, you have to learn normalization. Without that, you aren't doing any SQL.