anchor.diff:  base_table_def -> CREATE USER NAME identified opt_user_opts_list                                : {'create_user', unwrap_bin('$3'), '$4', '$5'}.
   drop_table_def -> DROP TABLE opt_exists table_list opt_restrict_cascade                         : list_to_tuple(['drop_table', {'tables', '$4'}] ++ '$3' ++ '$5').
   
  +% - alter_user_def -> ALTER USER user_spec
  +% - 
  +% - user_spec -> user_list proxy_clause
  +% - user_spec -> NAME spec_list
  +% - 
  +% - spec_list -> identified spec_list 
  +% - spec_list -> user_opt spec_list  
  +% - spec_list -> user_role spec_list 
  +
   identified -> IDENTIFIED BY NAME                                                                : {'identified_by', unwrap_bin('$3')}.
   identified -> IDENTIFIED EXTERNALLY opt_as                                                      : {'identified_extern', '$3'}.
   identified -> IDENTIFIED GLOBALLY opt_as                                                        : {'identified_globally', '$3'}.
  
positive.code:  schema_element
   base_table_def
   drop_table_def
   base_table_element_commalist
   base_table_element
   column_def
  
negative.code:  UNLOCK
   QUOTA
   UNLIMITED
   ALTER
   'AND'
   'NOT'
   'OR'
  