Use database links

admin — Fri, 23 Oct 2009 12:04:05 +0000

Once a database link has been created
you are now ready to select your data from the remote database referenced by the db link.

The syntax is :

select from

For example:

SQL> select * from dept@remotedb;

    DEPTNO DNAME          LOC
---------- -------------- -------------
        10 ACCOUNTING     NEW YORK
        20 RESEARCH       DALLAS
        30 SALES          CHICAGO
        40 OPERATIONS     BOSTON

The database link is opened during the select (or other DML transaction) and remains open for the duration of the session.
After you close a session, the links that were active in the session are automatically closed.

Close a db link

To explicitly close the database link , use the command below:

SQL> alter session close database link remotedb;

Session altered.

Using db links in other DML statements

You can use insert/update/delete statements just as easily with database links

SQL> select * from dept@remotedb;

    DEPTNO DNAME          LOC
---------- -------------- -------------
        10 ACCOUNTING     NEW YORK
        20 RESEARCH       DALLAS
        30 SALES          CHICAGO
        40 OPERATIONS     BOSTON

SQL> insert into dept@remotedb (deptno,dname,loc)
  2  values (50,'MARKETING','BOISE');

1 row created.

SQL> commit;

Commit complete.

SQL> select * from dept@remotedb;

    DEPTNO DNAME          LOC
---------- -------------- -------------
        10 ACCOUNTING     NEW YORK
        20 RESEARCH       DALLAS
        30 SALES          CHICAGO
        40 OPERATIONS     BOSTON
        50 MARKETING      BOISE

SQL> update dept@remotedb set loc = 'LONDON'
     where deptno = 50;

1 row updated.

SQL> commit;

Commit complete.

SQL> select * from dept@remotedb;

    DEPTNO DNAME          LOC
---------- -------------- -------------
        10 ACCOUNTING     NEW YORK
        20 RESEARCH       DALLAS
        30 SALES          CHICAGO
        40 OPERATIONS     BOSTON
        50 MARKETING      LONDON

SQL> delete from dept@remotedb
     where dname = 'MARKETING';

1 row deleted.

SQL> commit;

Commit complete.

SQL> select * from dept@remotedb;

    DEPTNO DNAME          LOC
---------- -------------- -------------
        10 ACCOUNTING     NEW YORK
        20 RESEARCH       DALLAS
        30 SALES          CHICAGO
        40 OPERATIONS     BOSTON

Note that DDL operations are not allowed through a database link:

SQL> alter table dept@remotedb
     add column (manager varchar2(30));

alter table dept@remotedb add column
(manager varchar2(30))
                 *
ERROR at line 1:
ORA-02021: DDL operations are not allowed
           on a remote database

Oracle Database Tips blog » db link usage syntax

Use database links

Close a db link

Using db links in other DML statements

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