SQL is a difficult acronym for a difficult language, but what it does is shuttle information into and out of your database in an organized manner. Your web applications and developers have to speak it, and your database – whether Oracle, MySQL, Postgres or some other will return information back using this computing dialect.
Since every movement on your website, from page to page (sessions) and purchase to purchase all involve interaction using these queries, writing them well can have a huge impact on your website performance. How big? We’ve fixed queries by adding indexes or rewriting them and seen improvements by as much as 100x. That’s converting pages that take ten seconds to ones that take 1/10 of a second. Be especially vigilant about those queries generated by Object Relational Mappers like Active Record, Ruby’s ORM layer.