SQL (Structured
Query Language) is a special-purpose programming language designed for storing, manipulating
and retrieving data stored
in a Relational
Database Management System (RDBMS).SQL consists of a data definition language
and a data manipulation language. 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 enhanced several times with added features. Most Relational Database Management Systems like MS
SQL Server, Microsoft Access, Oracle, MySQL, DB2, Sybase, PostgreSQL and
Informix use SQL as a database querying language.
Different Products of RDMS are:
Oracle
|
Oracle Corporation
|
SQL Server 2000
|
Microsoft
Corporation
|
DB2 UDB
|
IBM
|
My SQL
|
My SQL
|
Sybase
|
Sybase
|
In SQL we have
standard commands to interact with Relational Database. Those commands are Create, Alter, Truncate, and
Drop. These Commands can be classified into groups based on their nature.
1) DDL - Data Definition Language
2) DML- Data Manipulation Language
3) DQL- Data Query Language
4) DCL- Data Control Language
5) TCL- Transaction Control Language
1)DDL - Data Definition Language: These Statements (Commands) are used to
Create, Insert, Modify and Drop Database Objects.
Some Examples:
a) Create: Create Statement is used to make a new
database, table, index, or stored procedures.
By
using Create Statement we are creating a table in Database. Tables are organized
into rows and columns.
Syntax
for Create Statement:
Create
Table tablename (Column Name1 data type(size),
Column Name1 data type(size), Column Name2 data type(size), Column Name3 data
type(size), ………);
Here:
§ The column
name represents specify the names of the columns of the table.
§ The data
type parameter represents which type of data the column can hold (e.g. varchar integer,
date etc.).
§ The size
parameter represents the maximum length of the column of the table.
Example
for Create Statement:
Create Table Employee
(empid int (20), First Name Varchar(50),
Last Name Varchar(50), Deportment varchar(50), Address Varchar(50),City Varchar
(50));
Table name is Employee
In this table empid column is represents int data type and it will hold
an integer Value. Last Name, First Name, Deportment, Address and City columns
are of type varchar and will hold characters, and the maximum length for these
fields is 50 characters.
The empty "Employee" table will now look like this:
|
|
|
|
|
empid
|
First Name
|
Last Name
|
Deportment
|
Address
|
City
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2) DML- Data Manipulation Language: These Statements (Commands) are used to Insert,
Update and Delete Database Objects.
3) DQL- Data Query Language: These Statements (Commands) are used Select Commands
4) DCL- Data Control Language: These Statements (Commands) are used to create roles, permissions, and referential integrity as well it is
used to control access to database by securing it.
Examples: GRANT,
REVOKE statements
5) TCL- Transaction
Control Language: These Statements (Commands) are used to manage different transactions occurring within a database.
Examples: COMMIT,
ROLLBACK statements