value_spec 

<value_spec> ::=
  <
literal>
| <
parameter_spec>
| NULL
| USER
| USERGROUP
| LOCALSYSDBA
| SYSDBA [(<
user_name>)]
| SYSDBA [(<
usergroup_name>)]
| [<owner>.]<
sequence_name>.NEXTVAL
| [<
owner>.]<sequence_name>.CURRVAL
| DATE
| TIME
| TIMESTAMP
| TIMEZONE
| TRUE
| FALSE
| TRANSACTION
| UTCDIFF