What Is Sql?
Structured Query Language (SQL) is a standard query language. It is usually used with all relational databases for data manipulation and definition.
All the relational systems support SQL, therefore allowing migration of database from one DBMS to a different. In fact, this is one of the reasons of the main success of Relational DBMS. A user may be capable to write a program using SQL for an application that includes data being stored in more than one DBMSs, given these DBMS support standard SQL. This feature is usually referred to as portability. Though, not all the features of SQL executed in one RDBMS are available in others because of customization of SQL. Though, please note there is just ONE standard SQL.
SQL gives an interface where the user can state "What" are the expected results. The query implementation plan and optimisation is performed by the DBMS. The query plan and optimisation shows how a query needs to be implemented. For instance, if three tables X, Y and Z are to be joined mutually then which plan (X JOIN Y) and then Z or X JOIN (Y JOIN Z) may be implemented. All these decisions are depend on statistics of the relations.
SQL is known as a non-procedural language as it just states what is to be dome rather than how it is to be complete. Also, as SQL is a higher-level query language, it is closer to a language like English. Thus, it is very user friendly.
The American National Standard Institute (ANSI) has designed standard versions of SQL. The first standard in this series was formed in 1986. It was known as a SQL-86 or SQL1. This standard was revised and better later and SQL-92 or SQL-2 was released. A newer standard of SQL is SQL3 which is also called as SQL- 99. In this part we will try to cover features from latest standards. Though, some features may be found to be very specific to definite DBMS.
Some of the main features of SQL are:
- It is an English-like language.
- It is a non procedural language.
- It can process a one record as well as sets of records at a time.
- It is dissimilar from a third generation language (C& COBOL). All SQL
Statements describe what is to be complete rather than how it is to be complete.
- SQL is a data sub-language having of three built-in languages: Data definition language (DDL), Data manipulation language (DML) and Data control language (DCL).
- It insulates the user from the underlying algorithm and structure.
- SQL has facilities for defining database security, views, integrity constraints, transaction controls, etc.