create database link "database_link_name"
connect to username
identified by "password"
using 'connection_name';
select distinct db_link, created from dba_db_links where db_link='DB LINK NAME';
These views are helpful for working with DB links in Oracle:
DBA_DB_LINKS - All DB links defined in the database
ALL_DB_LINKS - All DB links the current user has access to
USER_DB_LINKS - All DB links owned by current user
