http://www.codeproject.com/Articles/33052/Visual-Representation-of-SQL-Joins http://nosql.mypopescu.com/post/51770099382/sql-joins-visualized

With IN and subquery / or "top" like keywords - http://javarevisited.blogspot.com.au/2012/12/how-to-find-second-highest-or-maximum-salary-sql.html

Top 5 Online Courses to Learn SQL and Database for Beginners - Best of Lot 
 - https://dev.to/javinpaul/5-online-courses-to-learn-sql-and-database-for-beginners-best-of-lot-5533