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Oracle® Database SQL Reference 10g Release 2 (10.2) Part Number B14200-02 |
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# Distributed Queries

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.

See Also: "Referring to Objects in Remote Databases" for more information on referring to database links Oracle Net Services Administrator's Guide for information on accessing remote databases

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. For example, the following statement raises an error because it selects `press_release`, a `LONG` value, from the `print_media` table on the `remote` database and locks the `print_media` table on the `local` database:

    SELECT r.product_id, l.ad_id, r.press_release
       FROM pm.print_media@remote r, pm.print_media l
       FOR UPDATE OF l.ad_id;

In addition, Oracle Database currently does not support distributed queries that select user-defined types or object `REF` datatypes on remote tables.