oracle undotbs usage

1-- UNDO tablespace current usage / available space
2SELECT a.TABLESPACE_NAME, SIZEMB, USAGEMB, (SIZEMB - USAGEMB) AS FREEMB
3FROM (SELECT round(sum(BYTES) / 1e6) AS SIZEMB, b.TABLESPACE_NAME
4      FROM DBA_DATA_FILES a, DBA_TABLESPACES b
5      WHERE a.TABLESPACE_NAME = b.TABLESPACE_NAME AND b.CONTENTS LIKE 'UNDO'
6      GROUP BY b.TABLESPACE_NAME) a,
7     (SELECT c.TABLESPACE_NAME, sum(BYTES) / 1e6 AS USAGEMB
8      FROM DBA_UNDO_EXTENTS c
9      WHERE STATUS <> 'EXPIRED'
10      GROUP BY c.TABLESPACE_NAME) b
11WHERE a.TABLESPACE_NAME = b.TABLESPACE_NAME;

1-- UNDOTBS usage per User:
2SELECT u.TABLESPACE_NAME          AS TABLESPACE,
3       s.USERNAME,
4       u.STATUS,
5       sum(u.BYTES) / 1024 / 1024 AS SUM_IN_MB,
6       count(u.SEGMENT_NAME)      AS SEG_CNTS
7FROM DBA_UNDO_EXTENTS u, V$TRANSACTION T, V$SESSION s
8WHERE T.ADDR = s.TADDR
9GROUP BY u.TABLESPACE_NAME, s.USERNAME, u.STATUS
10ORDER BY 1, 2, 3;