SQL AN OVERVIEW
What is SQL?
SQL is an acronym of Structured Query Language. It is built to work around Relational Databases which are sets of related information stored in tables. SQL was introduced by IBM as the language to interface with its prototype relational database management system, SYSTEM R. The first commercially available SQL relational database management was introduced in 1979 by Oracle Corporation.
Benefits of SQL?
1. SQL has become the database language of choice because it is flexible, powerful, and easy to learn.
2. SQL is a non-procedural language. Process sets of records rather than just one at a time and provides automatic navigation to the data.
3. SQL provides commands for a variety of tasks including: querying data, creating, updating and replacing objects and inserting, updating and deleting rows.
4. All major relational database management systems support SQL thus one can transfer all the skills gained with SQL from one RDBMS to another. Programs written in SQL are portable; they can often be moved from one database system to another with little modification.
Division of SQL
Every SQL statement begins with a command word key phrase. There are three major categories.
1. Data Definition Language (DDL)
Data definition language is a set of commands that defines database objects.
Create (New database objects)
Alter (Existing database objects)
Drop (Existing database objects)
2. Data Manipulation Language (DML)
Select (to query)
Update (modifying tables)
Insert (adding new records)
Delete (remove existing records)
3. Data Control Language (DCL)
Grant (Create user, provides database objects access)
Revoke (Revokes the user, revokes database objects access)
Commit (Commit the changes)
Rollback (Nullify the changes)