Oracle 查看占用undo大的sql語句

select 
s.sid,s.serial#,
s.sql_id,
v.usn,
segment_name,
r.status, 
v.rssize/1024/1024 mb
     from 
dba_rollback_segs r, 
v$rollstat v,
v$transaction t,
v$session s
     Where 
r.segment_id = v.usn and 
v.usn=t.xidusn and 
t.addr=s.taddr
order by segment_name;