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Oracle Database Links and MySQL Fully-Qualified Table Names

Oracle Usage

Database Links are schema objects used to interact with remote database objects such as tables. Common use cases for database links include selecting data from tables that reside in a remote database.

To use database links, Oracle net services must be installed on both the local and remote database servers to facilitate communications.

Examples

Create a database link named remote_db. When creating a database link, you have the option to specify the remote database destination using a TNS Entry or to specify the full TNS Connection string.

CREATE DATABASE LINK remote_db CONNECT TO username IDENTIFIED BY password USING 'remote';

CREATE DATABASE LINK remotenoTNS CONNECT TO username IDENTIFIED BY password
  USING '(DESCRIPTION=(ADDRESS_LIST=(ADDRESS = (PROTOCOL = TCP)(HOST =192.168.1.1)
  (PORT =1521)))(CONNECT_DATA =(SERVICE_NAME = orcl)))';

After the database link is created, you can use the database link directly as part of a SQL query using the database link name @remote_db as a suffix to the table name.

SELECT * FROM employees@remote_db;

Database links also support DML commands.

INSERT INTO employees@remote_db
(employee_id, last_name, email, hire_date, job_id) VALUES
(999, 'Claus', 'sclaus@example.com', SYSDATE, 'SH_CLERK');

UPDATE jobs@remote_db SET min_salary = 3000 WHERE job_id = 'SH_CLERK';

DELETE FROM employees@remote_db WHERE employee_id = 999;

For more information, see Managing Database Links in the Oracle documentation.

MySQL Usage

Currently, MySQL doesn’t provide a direct comparable alternative for Oracle Database Links. You can use the fully-qualified names to query data from another database within the same cluster. This functionality is similar to querying data from a different schema in Oracle. If the data cannot be stored under the same MySQL Cluster, then there is no equivalent to Oracle Database Links in MySQL.

If the data can’t be placed under the same MySQL Cluster then there is no relevant equivalent to Oracle Database Links in MySQL.

Examples

Query all flight ids from the all_flights table in the flights database, assume that this code runs from another database.

SELECT flight_id from flights.all_flights;

This query returns the data only if the user has permissions to the table and the database.