Undo DDL statement on View in Oracle
Depending on the version of Oracle and whether you have the appropriate privileges (FLASHBACK ANY TABLE) and if the change was relatively recent,

SELECT text
  FROM dba_views AS OF TIMESTAMP( systimestamp - interval '1' hour )
 WHERE owner = &lt;&lt;owner of view&gt;&gt;
   AND view_name = &lt;&lt;name of view&gt;&gt;


will give you the text of the view definition as of an hour ago.  You can obviously adjust the flashback time to a timestamp just before the DDL you want to undo.