The Oracle distributed database management system architecture lets you access data in remote databases using Oracle Net and an Oracle Database server. You can identify a remote table, view, or materialized view by appending @
dblink to the end of its name. The
dblink must be a complete or partial name for a database link to the database containing the remote table, view, or materialized view.
References to Objects in Remote Databases for more information on referring to database links
Restrictions on Distributed Queries
Distributed queries are currently subject to the restriction that all tables locked by a
UPDATE clause and all tables with
LONG columns selected by the query must be located on the same database. In addition, Oracle Database currently does not support distributed queries that select user-defined types or object
REF data types on remote tables.