SQL Concepts

SQL is a descriptive, entity-oriented query language for data manipulation with its roots in relational algebra. Today SQL is used either as a stand-alone programming language or within other languages like C, C++, Java, ADA, COBOL, FORTRAN, PL/1, PASCAL etc.

SQL actually consists of three sub languages:

• DDL - Data Definition Language: Used for creating databases and tables and for maintaining the structure.
• DML - Data Manipulation Language: Used for accessing and extracting data from a database (add, update, delete etc.).
• DCL - Data Control Language: Used to control access to the database and therefore essential for the security system.

In most implementations of SQL functions from other programming languages (if-clauses, iterations etc.) have been added. Some SQL-versions, such as Oracle's PL/SQL, can therefore be seen as independent programming languages.