SQL is a standard computer language used to operate relational databases, that is to say, a stock of information organized in tables in the relational data model. PostgreSQL is an open source relational database management system. Its stable behavior and extensive programming options make it a widely recognized management system that can handle very large volumes of data. It operates on a traditional client / server architecture. MySQL and Oracle are the two other most used relational database management systems. While PostgreSQL has a sophisticated queries planner allowing it to effectively reach quite a lot of tables, MySQL is instead focused on the optimization of simple queries. PostgreSQL and Oracle have far more similarities between them. Their main differentiation lies in their cost of acquisition, Oracle being considered as quite expensive while PostgreSQL is open source.