SQL> desc v$mystat
 Name                             Null?    Type
 -------------------------------- -------- ----------------------
 SID                                       NUMBER
 STATISTIC#                                NUMBER
 VALUE                                     NUMBER

SQL> select statistic#, name from v$statname where name like '%undo%';
STATISTIC# NAME
---------- -----------------------------------------------------------
        75 DBWR undo block writes
       176 undo change vector size
       177 transaction tables consistent reads - undo records applied
       179 data blocks consistent reads - undo records applied
       188 rollback changes - undo records applied
       200 auto extends on undo tablespace
       202 total number of undo segments dropped
       220 global undo segment hints helped
       221 global undo segment hints were stale
       222 local undo segment hints helped
       223 local undo segment hints were stale
       224 undo segment header was pinned
       226 SMON posted for undo segment recovery
       229 SMON posted for undo segment shrink
       236 IMU undo retention flush
       242 IMU undo allocation size

16 rows selected.