Nice article. I will be following you. Please see my blogpost on learning SQL Injection manually: https://steemit.com/infosec/@netscape101/how-to-learn-sql-injection
http://www.infosectoughguy.com/2017/06/how-to-learn-sql-injection.html
I would highly recommend people try hacking Damn Vulnerable Web app. You can run it on a VM on your local machine and attack it with SQLMap.
http://www.dvwa.co.uk/