This query DOES NOT show the TEMP tablespace!
select a.tablespace_name, file_name, b.bytes, a.status
from dba_tablespaces a, dba_data_files b
where a.tablespace_name = b.tablespace_name

This query DOES show the TEMP tablespace but still not the datafile (outer join with dba_data_files)!
select a.tablespace_name, file_name, b.bytes, a.status
from dba_tablespaces a, dba_data_files b
where a.tablespace_name = b.tablespace_name (+)

I also tried joins with v$sort_segment, v$datafile and Oracle still refuses to show the datafile but does show the tablespace WHY?

I thought there might be some thing wrong with TEMP with the dB/Instance but I ran this for 4 different instances/dB.