A typical database management system (DBMS) allows users to store, access, and modify data in an organized, efficient way. Originally, each DBMS had its own application programming interface (API) used for development of client programs working with a DBMS. While these clients often had friendly interface for non-technical users, their development required a programmer with the knowledge of the used DBMS. Because of this, it was hard to migrate from one DBMS to another.
Structured Query Language (SQL) is an aid how to work with all DBMS in one uniform way. It consists from Data Definition Language (DDL) and Data Manipulation Language (DML). As DDL is used to create, delete, alter tables and etc., DML provides way how insert, delete, update and select records. It is not a procedural language; i.e. it determines what to do and not how.
In another words SQL is a language allowing users to express their requests - access data, on an ad-hoc basis.
SQL became an ANSI standard in 1986 and an ISO standard in 1987; it is used today in many great database management systems.
There are two possible pronunciations of SQL: former “ess-cue-ell” and “sequel”.