DB level size and free space

col hostname for a30
select (select host_name from v$instance)hostname,GB_DB_SIZE  , (select sum(BYTES)/1024/1024/1024 from dba_free_space) free from
(
select sum(physical_bytes)/1024/1024/1024 GB_DB_SIZE  from
(
select
      sum(bytes) physical_bytes
    from
      dba_data_files
    union all
select
      sum(bytes)
    from
      dba_temp_files
union all
select sum(BYTES) from v$log
) );