select  *  from USER_UNUSED_COL_TABS;

ALTER TABLE TEST_TABLE DROP UNUSED COLUMNS;

SQL> alter table t set unused column col;

Table altered.

SQL> alter table t set unused column col2;

Table altered.

SQL> select undo_sql from FLASHBACK_TRANSACTION_QUERY
  2  where table_owner='SYS' and table_name='COL$'
  3    and undo_sql like 'update%'
  4    and trunc(COMMIT_TIMESTAMP) = trunc(sysdate)
  5  order by commit_scn;
UNDO_SQL
------------------------------------------------------------------------------------------------------------------------
update "SYS"."COL$" set "COL#" = '2', "SEGCOL#" = '2', "SEGCOLLENGTH" = '22', "NAME" = 'COL', "TYPE#" = '2', "LENGTH" =
'22', "FIXEDSTORAGE" = '0', "PRECISION#" = NULL, "SCALE" = NULL, "NULL$" = '0', "DEFLENGTH" = NULL, "PROPERTY" = '0', "C
HARSETID" = '0', "CHARSETFORM" = '0', "SPARE1" = '0', "SPARE2" = '0', "SPARE3" = '0' where ROWID = 'AAAAACAABAAAZEYAAH';
------------------------------------------------------------------------------------------------------------------------
update "SYS"."COL$" set "COL#" = '2', "SEGCOL#" = '3', "SEGCOLLENGTH" = '22', "NAME" = 'COL2', "TYPE#" = '2', "LENGTH" =
 '22', "FIXEDSTORAGE" = '0', "PRECISION#" = NULL, "SCALE" = NULL, "NULL$" = '0', "DEFLENGTH" = NULL, "PROPERTY" = '0', "
CHARSETID" = '0', "CHARSETFORM" = '0', "SPARE1" = '0', "SPARE2" = '0', "SPARE3" = '0' where ROWID = 'AAAAACAABAAAZEYAAI'
;
------------------------------------------------------------------------------------------------------------------------

2 rows selected.

SQL> select u.name owner, o.name table_name
  2  from sys.user$ u, sys.obj$ o
  3  where u.user# = o.owner#
  4    and o.obj# in
  5        (select obj# from sys.col$ where rowid in ('AAAAACAABAAAZEYAAH','AAAAACAABAAAZEYAAI'))
  6  /
OWNER                          TABLE_NAME
------------------------------ ------------------------------
MICHEL                         T

SQL> begin
  2    sys.dbms_logmnr.add_logfile (logfilename=>'E:\ORACLE\BASES\MIKB2\RL_G1_1.RDO',
  3                                 options=>sys.dbms_logmnr.NEW);
  4    sys.dbms_logmnr.add_logfile (logfilename=>'E:\ORACLE\BASES\MIKB2\RL_G2_1.RDO',
  5                                 options=>sys.dbms_logmnr.ADDFILE);
  6    sys.dbms_logmnr.add_logfile (logfilename=>'E:\ORACLE\BASES\MIKB2\RL_G3_1.RDO',
  7                                 options=>sys.dbms_logmnr.ADDFILE);
  8    sys.dbms_logmnr.add_logfile (logfilename=>'E:\ORACLE\BASES\MIKB2\RL_G4_1.RDO',
  9                                 options=>sys.dbms_logmnr.ADDFILE);
 10    sys.dbms_logmnr.start_logmnr (
 11      startTime => trunc(sysdate),
 12      endTime   => sysdate,
 13      options   =>   sys.dbms_logmnr.skip_corruption
 14                   + sys.dbms_logmnr.committed_data_only
 15                   + sys.dbms_logmnr.dict_from_online_catalog
 16    );
 17  end;
 18  /

PL/SQL procedure successfully completed.

SQL> col seg_owner format a10
SQL> col sql_redo format a80
SQL> select seg_owner, sql_redo
  2  from v$logmnr_contents
  3  where ( operation like 'ALTER%' or operation = 'DDL' )
  4    and lower(sql_redo) like '%set unused%'
  5  /
SEG_OWNER  SQL_REDO
---------- --------------------------------------------------------------------------------
MICHEL     alter table t set unused column col;
MICHEL     alter table t set unused column col2;

2 rows selected.

SQL> exec sys.dbms_logmnr.end_logmnr;

PL/SQL procedure successfully completed.