ALTER USER --+--> <username> --++------------------------+--->
               +--> PUBLIC ------+++-> alter-user-opts --+-+
                                   +----------<----------+

  alter-user-opts =

  -+-> ACCOUNT -----+--> LOCK ----+----------------------------------+->
   |                +--> UNLOCK --+                                  |
   +-> IDENTIFIED EXTERNALLY ----------------------------------------+
   +-> RENAME TO ------> <new-username> -----------------------------+
   +-> COMMENT IS --+--> '<string>' ---------+-----------------------+
   |                +-------- / <------------+                       |
   +-> NO PROFILE ---------------------------------------------------+
   +-> PROFILE <profile_name> ---------------------------------------+