DDL- (Data Definition Language)

These commands help you to manage the database structure. When you execute DDL commands then auto-commit takes place at the end of the transaction. The lists of DDL Commands are.

1) CREATE

This command is used to create database and database objects.

Example

To create a database

CREATE DATABASE DB1;

To create objects in the database

CREATE TABLE L1(
A NUMBER(4)
);

2) DROP

This command is used to drop database and database objects.

Example

To drop database

DROP DATABASE DB1;

To drop objects in the database

DROP TABLE L1;

3) ALTER

This allows you to rename an existing table and It can also be used to add, modify, or drop a column from an existing table.

Example

To add a column to a table

ALTER TABLE L1 ADD B VARCHAR2(4) NOT NULL;

To drop a column from a table

ALTER TABLE L1 MODIFY B NUMBER(5);

To modify a column from a table

ALTER TABLE L1 DROP COLUMN B;

To rename a database object

ALTER TABLE L1 RENAME TO L2;

4) RENAME

This command is used to rename an object in the database.

Example

RENAME L60 TO T1;

5) TRUNCATE

It deletes all data from the table. Actually, truncate doesn’t remove data but de-allocates whole Data pages and pointers to index.

Example

TRUNCATE TABLE L1;

•  It is much faster.
•  We can’t use condition if a statement contains Truncate.
•  A trigger doesn’t fire on truncate.
•  It cannot be rolled back.

6) COMMENTS

Example

To create comment on column

COMMENT ON COLUMN EMPL.FNAME IS 'MAIDON NAME';

To alter comment on column

COMMENT ON COLUMN EMPL.FNAME IS 'MAIDON NAME IS FATHER NAME';

To drop comment on column

COMMENT ON COLUMN EMPL.FNAME IS '';