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Oracle: DBA_OBJECTS - Columns CREATED, LAST_DDL_TIME and TIMESTAMP

dba_objects has three columns that store date-related information:
Name Data type Comment
created date Corresponds to the point in time when the corresponding objects was created.
last_ddl_time date Last modification (DDL statement) of the object or dependent objects. This includes grants and revokes
timestamp varchar2 Last modification of the structure (specification) of the object. In the case of a view, the structure is considered changed if the number, data types, names (or order of columns?) of the returned columns change.
The datatype of created and last_ddl_time is date, the datatype of timestamp is varchar2 (!) in the format YYYY-MM-DD:HH24:MI:SS. 
select
   obj.object_name,
   obj.subobject_name,
   obj.object_type,
   obj.created,
   obj.last_ddl_time,
   to_date(obj.timestamp, 'YYYY-MM-DD:HH24:MI:SS') timestamp_,
   obj.status
from
   user_objects obj
where
-- obj.object_name     like '%FOOBAR%'     and
   obj.object_name not like 'TQ84%'        and
   obj.object_name not like 'ERR$%'        and
   obj.object_type not in ('INDEX', 'LOB')
order by
   obj.timestamp desc;

CREATED <= TIMESTAMP <= LAST_DDL_TIME

In most cases, created <= timstamp and timstamp <= last_ddl_time, although there are some exceptions, especially in the SYS, SYSTEM, XDB, WMSYS and GSMADMIN_INTERNAL schemas: 
select
   count(*),
   owner,
   object_type
from
    dba_objects
where
   to_date(timestamp, 'yyyy-mm-dd:hh24:mi:ss') not between created and last_ddl_time
group by
   owner,
   object_type
order by
   owner,
   object_type;

See also

dba_objects

Index