Postgres

• http://tech.pro/tutorial/1555/10-easy-steps-to-a-complete-understanding-of-sql
• http://www.postgresql.org/docs/current/static/using-explain.html
• http://blog.heapanalytics.com/dont-iterate-over-a-postgres-array-with-a-loop/
• http://use-the-index-luke.com/blog/2013-08/its-not-about-the-star-stupid
• http://www.citusdata.com/blog/76-postgresql-columnar-store-for-analytics
• http://johtopg.blogspot.se/2014/04/upsertisms-in-postgres.html?m=1

CS

• http://codon.com/programming-with-nothing
• http://jlongster.com/2011/12/16/sicp-26-church-notation.html
• https://www.codefellows.org/blog/trees-as-graphs-vs-trees-as-data-structures

Ruby/JS

• http://codecombat.com/
• http://www.codewars.com/
• http://awaxman11.github.io/blog/2013/08/05/what-is-the-difference-between-a-block/

Rails

• http://www.amberbit.com/blog/2014/2/4/postgresql-awesomeness-for-rails-developers/
• http://svs.io/post/59495114366/roll-your-own-web-framework-in-half-an-hour
• http://anilpunjabi.tumblr.com/post/25948339235/ruby-and-rails-interview-questions-and-answers
• https://gist.github.com/ryansobol/5252653
• http://thereq.com/q/best-ror-software-interview-questions/hard

Regex

• http://www.regexr.com/
• http://qntm.org/files/re/re.html