value_spec 

<value_spec> ::=
  <literal>
| <parameter_spec>
| NULL
| USER
| USERGROUP
| SYSDBA
| CURRENT_SCHEMA
| UID
| [<schema_name>.]<sequence_name>.NEXTVAL
| [<schema_name>.]<sequence_name>.CURRVAL
| <table_name>.CURRVAL
| DATE
| TIME
| TIMESTAMP
| UTCDATE
| TIMEZONE
| UTCDIFF
| TRUE
| FALSE
| TRANSACTION