Structure Query Language
Structure Query Language (SQL) is the most popular and widely used relational standard database language. It is easy to learn and use. It allows the user to define, retrieve and to manipulate the data in the table of database. It was designed and implemented at IBM Research as an interface in an experimental relational database system called System R. This language became the basis for IBM’s first commercially available relation database system. This language is accepted as a standard database language by ANSI and ISO.
The development of SQL began at IBM in the mid-1970s under the name SEQUEL. In 1980, it was renamed as SQL. The ANSI SQL standards were published first in 1968 and updated in 19989 and 1992. The standard versions are SQL-86, SQL-92 and most recent standard version is SQL3, which is concerned to object-oriented programming and other recent database concepts. Structure Query Language is now the standard database language and is used in many commercial DBMS such as DB2, Oracle, SQL Server, INGRES, Sybase, and Microsoft Access etc.
SQL is a comprehensive database language. It is complete data definition language (DDL) and data manipulation language (DML). Its statement are like English Statement.
SQL is not a general purpose programming language like C++, Visual Basic but it is a data sub-language or data access language. Its statement can be embedded into programs written in general purpose languages such as Visual Basic, C++ etc.
Therefore the main feature of SQL are
- SQL statements can be executed on any computer (main-frame and personal computer) and under any operating system.
- The SQL statement or commands accept one or more relations as input and returns a single relation as output.
- SQL follows the relational calculus style. The syntax of SQL statements are also similar to the relational calculus operations.
- It has featured for defining views on database.
- It has featured for specifying security and authorization.
- It has featured for defining integrity constraints.
- It also featured for specifying transaction controls.
Both ANSI and ISO have accepted SQL as the standard language for the relational databases. SQL statements are used to perform different operations on the databases such as to retrieve data from database tables, enter new data in databases and to change data or to delete the data of database etc.Similarly you can define the structure of databases and can change the existing structures of databases.
All these functions are performed on the databases through SQL statements. The statements of SQL are English like statement. Different statements are used to perform different functions. On the basis of SQL statement, SQL is categorized as
- SQL as Data Retrieval Language
- SQL as Data Manipulation Language
- SQL as Data Definition Language
- SQL as Transaction Control Language. For this purpose, SQL provides statement that are used to manage the change in the data of database made by DML statements
- Data Control Language (DCL). For this purpose, SQL provides statement that are used to give or remove access rights.