How to create dblink or drop dblink in oracle

 In Oracle, a database link (dblink) is a schema object in one database that enables you to access objects in another database. This is useful for distributed database systems where you need to perform operations or retrieve data from a remote database.

Creating a Database Link

Basic Syntax

CREATE DATABASE LINK dblink_name
CONNECT TO remote_user IDENTIFIED BY remote_password
USING 'tns_service_name';

• dblink_name: The name of the database link.
• remote_user: The username on the remote database.
• remote_password: The password for the remote user.
• tns_service_name: The TNS service name that resolves to the remote database.

Examples

1. Creating a Basic Database Link

Assume you have a remote database with the TNS service name remote_db and a user remote_user with password remote_password.

CREATE DATABASE LINK remote_dblink
CONNECT TO remote_user IDENTIFIED BY remote_password
USING 'remote_db';

2. Using a Database Link

After creating the dblink, you can use it to query data from the remote database.

Querying a Table

SELECT * FROM employees@remote_dblink;

Joining Local and Remote Tables

SELECT l.local_column, r.remote_column
FROM local_table l
JOIN remote_table@remote_dblink r ON l.id = r.id;

Performing DML Operations

You can also perform DML operations like INSERT, UPDATE, and DELETE using the database link.

Inserting Data

INSERT INTO employees@remote_dblink (employee_id, first_name, last_name)
VALUES (1001, 'John', 'Doe');

Updating Data

UPDATE employees@remote_dblink
SET salary = salary * 1.1
WHERE department_id = 10;

Deleting Data

DELETE FROM employees@remote_dblink
WHERE employee_id = 1001;

Managing Database Links

1. Viewing Existing Database Links

You can query the DBA_DB_LINKS or ALL_DB_LINKS view to see existing database links.

SELECT db_link, username, host
FROM dba_db_links;

Or for the current user:

SELECT db_link, username, host
FROM all_db_links;

2. Dropping a Database Link

To drop a database link, use the DROP DATABASE LINK statement.

DROP DATABASE LINK remote_dblink;

3. Public Database Links

A public database link can be accessed by all users in the database.

Creating a Public Database Link

CREATE PUBLIC DATABASE LINK public_dblink
CONNECT TO remote_user IDENTIFIED BY remote_password
USING 'remote_db';

Dropping a Public Database Link

DROP PUBLIC DATABASE LINK public_dblink;

Considerations

1. Security: Be cautious with the credentials used in database links. Ensure that the remote user has the appropriate privileges and that sensitive information is protected.

2. Performance: Accessing remote databases can introduce network latency. Optimize queries and consider using materialized views for frequently accessed remote data.

3. Dependency Management: Changes in the remote database, such as schema changes, can impact the functionality of the database link.

4. Privileges: Creating a database link requires the CREATE DATABASE LINK privilege. For public database links, you need the CREATE PUBLIC DATABASE LINK privilege.

Use Cases

1. Distributed Databases: Ideal for accessing and integrating data from distributed databases.
2. Data Migration: Useful for migrating data between databases.
3. Reporting and Analytics: Enable consolidated reporting from multiple data sources.
4. Application Integration: Allow different applications to share and access data seamlessly.

By leveraging database links, you can facilitate seamless communication and data exchange between different Oracle databases, enabling more robust and integrated database solutions.