Oracle 11g Release 2

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with tab0( str, value ) as
(
  select 'LOCKED AT: ','LOCKED ENTITY: ACCOUNT
  LOCKED BY USER: ops
  LOCKED AT: 31/05/2004 11:47
  CUST NOTES: <Please enter explanation here>
  Customer notes are entered here.
  UNLOCKED ENTITY: ACCOUNT
  UNLOCKED BY USER: ops
  UNLOCKED AT: 31/05/2004 11:49
  UNLOCK NOTES: <Please enter explanation here>
  Test
  LOCKED ENTITY: USER
  LOCKED BY USER: ops
  LOCKED AT: 31/05/2004 11:50
  LOCK NOTES: <Please enter explanation here>
  Test
  UNLOCKED ENTITY: USER
  UNLOCKED BY USER: ops
  UNLOCKED AT: 24/08/2009 16:47
  UNLOCKED NOTES: <Please enter explanation here>' from dual    
), tab as
(
select 
       regexp_substr(value,
              str||'([[:digit:]]{2}/[[:digit:]]{2}/[[:digit:]]{4}\.?)',1,level)
              as Dates_Locked,
       regexp_instr(value,
              str||'([[:digit:]]{2}/[[:digit:]]{2}/[[:digit:]]{4}\.?)',1,level)      
              as Pos_Unlocked,
       str, value       
   from tab0
connect by level <= regexp_count(value,str) 
)
select ltrim( Dates_Locked, str ) as Dates_Locked
  from tab     
 where not regexp_like(substr(value,Pos_Unlocked-2,2),'UN','i');

DATES_LOCKED
31/05/2004
31/05/2004