Database Links
A path to a remote database, allowing a user to treat tables in the
remote database as if they where local.
Database links cannot be altered only created and dropped.
For ease of administration always user the CONNECT TO string, if it is omitted
the current username and password is used to connect to the remote
database meaning that users and passwords must be kept in step.
To create a private link:
CREATE (PUBLIC or SHARED) DATABASE LINK name CONNECT TO user identified by password USING 'tsnames_alias';
This allows you to query, e.g. select * from v$parameter@name.xx.xxx.com;
You cannot select LONG values from a segment across a link.
The command 'create database link tony.pls2 etc' run within the
system schema creates a link called tony.pls2 in the system schema.
DBA_DB_LINKS shows all links, username is the user the link is connecting to.