Instance/database/schema/Host details

Oracle Database Name

select ora_database_name from dual

Oracle Instance Number

select ora_instance_num from dual

Oracle Current Schema

SELECT sys_context('USERENV', 'CURRENT_SCHEMA') 

  FROM dual;

 

Oracle Host Name

SELECT sys_context('USERENV', 'HOST')

  FROM dual;

 

Oracle Service Name 

 SELECT sys_context('USERENV', 'SERVICE_NAME')

  FROM dual;