The relational data model as proposed by Codd provided the basic concepts for a new database management system, the relational database management system (RDBMS). Soon after the relational model was defined, a number of relational database languages were developed and used for instructing the RDBMS. Structured Query Language being one of them.
The SQL language is so inextricably tied to relational database theory that it is impossible to discuss it without also discussing the relational data model.
The Structured Query Language is a relational database language. By itself, SQL does not make a DBMS. It is just a medium which is used to as a means of communicating to the DBMS what you want it to do. SQL commands consist of english like statements which are used to query, insert, update and delete data. What is the meaning of `English like , is that SQL commands resemble english language sentences in their construction and use. This does not mean that you can type in something like "Pull up the figures for last quarter s sales" and expect SQL to understand your request. What it does mean is that SQL is a lot easier to learn and understand than most of the other computer languages.