What is Data definition language?

Data Definition Language (DDL) in SQL

What is Data Definition Language (DDL)?

Data Definition Language (DDL) is a set of SQL commands used to define, create, modify, and delete database structures.

DDL commands are responsible for managing database objects such as:

• Tables
• Indexes
• Views
• Schemas
• Users (in some database systems)

DDL is an important subset of SQL (Structured Query Language) used in database applications.

Common DDL Commands

Some commonly used DDL commands include:

1. CREATE

The CREATE command is used to create new database objects, such as tables or indexes.

Example:

CREATE TABLE Students (

    StudentID INT,

    Name VARCHAR(50),

    Age INT

);

This command creates a new table named Students with specified columns.

2. ALTER

The ALTER command is used to modify an existing database object, such as adding or changing columns in a table.

Example:

ALTER TABLE Students

ADD Email VARCHAR(100);

This command creates a new table named Students with specified columns.

2. ALTER

The ALTER command is used to modify an existing database object, such as adding or changing columns in a table.

Example:

ALTER TABLE Students

ADD Email VARCHAR(100);

3. DROP

The DROP command is used to delete database objects permanently.

Example:

DROP TABLE Students;

This command deletes the Students table from the database.

Features of DDL

• DDL defines the structure of a database.
• It provides commands to create, modify, and delete database objects.
• It uses predefined SQL syntax to describe data structures.
• It allows defining column names and data types when creating tables.
• Some database systems also allow defining XML data structures using DDL.

How DDL Works

When a new table is created using SQL, the CREATE command is used along with:

• Table name
• Column names
• Data types

After creation:

• The table structure can be modified using the ALTER command.
• The table can be deleted using the DROP command.

DDL and Other SQL Languages

DDL is only one part of SQL. SQL is divided into different categories:

Examples of Other SQL Commands

• DML Commands:
  SELECT, INSERT, UPDATE, DELETE
• DCL Commands:
  GRANT, REVOKE

These commands are not part of DDL but are part of other SQL categories.