How large is the database

col "Database Size" format a20
col "Free space" format a20
col "Used space" format a20
select round(sum(used.bytes) / 1024 / 1024 / 1024 ) || ' GB' "Database Size"
, round(sum(used.bytes) / 1024 / 1024 / 1024 ) - 
 round(free.p / 1024 / 1024 / 1024) || ' GB' "Used space"
, round(free.p / 1024 / 1024 / 1024) || ' GB' "Free space"
from    (select bytes
 from v$datafile
 union all
 select bytes
 from  v$tempfile
 union  all
 select  bytes
 from  v$log) used
, (select sum(bytes) as p
 from dba_free_space) free
group by free.p
/