Database Server info

SELECT
user
,sys_context('USERENV', 'DB_UNIQUE_NAME') DB_UNIQUE_NAME
,sys_context('USERENV', 'HOST') HOST
,sys_context('USERENV', 'INSTANCE') INTSANCE
,sys_context('USERENV', 'SERVER_HOST') SERVER_HOST
,sys_context('USERENV', 'SID') SID
FROM dual

or
select name from v$database;