SQL is a structured query language which is primarily used for accessing and manipulating data in databases.
SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the International Organization for Standardization (ISO) in 1987. Since then, the standard has been revised to include a larger set of features. Despite the existence of such standards, though, most SQL code is not completely portable among different database systems without adjustments.
Dr. E. F. Codd published the paper, "A Relational Model of Data for Large Shared Data Banks", in June 1970 in the Association of Computer Machinery (ACM) journal, Communications of the ACM. Codd's model is now accepted as the definitive model for relational database management systems (RDBMS). The language, Structured English Query Language (SEQUEL) was developed by IBM Corporation, Inc., to use Codd's model. SEQUEL later became SQL (still pronounced "sequel"). In 1979, Relational Software, Inc. (now Oracle) introduced the first commercially available implementation of SQL. Today, SQL is accepted as the standard RDBMS language.
RDMS stands for Relational Database Management System. It is the basic of all the database systems like SQL, IBM DB2, Oracle, MySQL, Microsoft Access, Microsoft SQL Server and others.
In RDMS data is stored in the form of the object that is called table. A table has row and column relationship. So due to this relationship, it is known as relational database.