These statements define the structure of the database. DDL consist of those statements that create,alter and drop database objects and statements that grant and revoke privileges and roles to user  of the database.

Statements under this category are:

CREATE 

ALTER

DROP

GRANT

REVOKE etc.

Creating Database objects: Create command

Create statement used to create database objects.

e.g. Tables,Views, Synonyms etc.

Syntax of the CREATE TABLE statement

CREATE TABLE Table-name

( Column-name 1 data-type[column constraint],

 Column-name 2 data-type[column constraint],

 -              -                 -

 -              -                 -

Column-name ndata-type[column constraint],

[Table-constraints]  );

Following statement creates an EMPLOYEE -DETAILS table:

CREATE TABLE Employee-details

(  Emp_No       Number(6) PRIMARY KEY

  Emp_Name      Char(6) NOT NULL

  DEPT        Char(20)

  SALARY       Number

    Constraint     DEPT_CHECK

 CHECK(DEPT IN ('ACCOUNT','PERSONNEL','ADMIN'))

);

Altering definition of table : Alter command

ALTER TABLE command is used to alter the definition of a table in the database.

Syntax of the command:

ALTER TABLE Table_name

ADD           column-name data_type           [column_constraint],

[MODIFY         column-name data_type           [column_constraint]];

e.g. Alter table Employee-details add age number.