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.

Restrictions on Distributed Queries

Distributed queries are currently subject to the restriction that all tables locked by a FOR 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.