database link in oracle database

 Make sure we have database entries of target db in tnsnames.ora

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CREATE DATABASE LINK remote_db_link
CONNECT TO username IDENTIFIED BY password
USING 'remote_database_tns';

CREATE PUBLIC DATABASE LINK link_name
CONNECT TO username IDENTIFIED BY password
USING 'tns_string';

[oracle@pm admin]$ cat tnsnames.ora

chennai  =    # ----> this is "tns_string"

  (DESCRIPTION =

    (ADDRESS_LIST =

      (ADDRESS = (PROTOCOL = TCP)(HOST = pm.shaikh.com)(PORT = 1521))

    )

    (CONNECT_DATA =

      (SID = chennai)

    )

  )

SELECT * FROM remote_table@remote_db_link;

drop public database link db_link_name;

drop database link db_link_name;

select * from all_db_links;

select * from dba_db_links;

select * from user_db_links;

set lines 400;

col owner for a10;

col db_link for a30;

col username for a20;

col host for a20;

select owner,db_link,username,host from all_db_links;