Create DATABASE LINK

A database link is a schema object in one database that enables you to access objects on another database. The other database need not be an Oracle Database system. However, to access non-Oracle systems you must use Oracle Heterogeneous Services.
You might want to create a database link, for instance, if you want the data in a remote database updated when the local database is updated. Here’s how to accomplish this:
The first thing you need to do is to create a database link pointing to the other location. The database link can be created with a command similar to the following:
    CREATE [SHARED | PUBLIC] DATABASE LINK <link-name>
    [CONNECT TO <username> IDENTIFIED BY <password>]
    [USING <connect-string>];
To create a fixed user database link, a username and password to connect with must be specified. For example:
    CREATE PUBLIC DATABASE LINK BASING
    CONNECT TO USRCRY IDENTIFIED BY CRYPWD
    USING BASING_ORA;
    Select count(*) from table@basing;
You’ll want to give the database link a better name, use the appropriate userid/password to connect to the remote database, and configure your TNSNAMES.ORA file with a TNS alias to point to that database.