Oracle dblink create cross-database operations

Create a dblink: create public database link link_to_test connect to the username 
IDENTIFIED by "Password Caps"
a using
'(the DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP) (HOST = cross-database ip address) (PORT = 1521))) ( CONNECT_DATA = (SERVICE_NAME = database service name))) '

Create synonyms: create synonym synonym name FOR database name @link_to_test;
use synonyms: select count (*) from a synonym name; check can achieve the effect of other libraries