Create Database link in Oracle Database 19c

 Syntax

SQL>  create database link <custom database link> 

        connect to <user> identified by
<password> using '(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=                <hostname>)
(PORT=<port number>))(CONNECT_DATA=(SID=<ORACLE_SID>)))';

Example:

  SQL> create database link XSCHLINK connect to aptest identified by aptest123

'(DESCRIPTION =(ADDRESS = (PROTOCOL=tcp)(HOST=apdb001.myorg.com) (PORT=1521)) (CONNECT_DATA = (SERVICE_NAME=ebs_TESTPDB)(INSTANCE_NAME=TESTCDB)))';