INTERVAL YEAR (year_precision) TO MONTH
Stores a period of time in years and months, where year_precision is the number of digits 
in the YEAR datetime field. Accepted values are 0 to 9. The default is 2.

INTERVAL DAY (day_precision) TO SECOND (fractional_seconds_precision)
Stores a period of time in days, hours, minutes, and seconds, where
day_precision is the maximum number of digits in the DAY datetime field. Accepted values 
are 0 to 9. The default is 2.
fractional_seconds_precision is the number of digits
in the fractional part of the SECOND field. Accepted
values are 0 to 9. The default is 6. 
 
CREATE TABLE test
          ( d_ymint                INTERVAL YEAR(2) TO MONTH,
            d_dsint                INTERVAL DAY(2) TO SECOND(6));
SQL> INSERT INTO dt VALUES 
          ( INTERVAL'12-01' YEAR TO MONTH,
            INTERVAL '50 10:20:20.123' DAY(2) TO SECOND(3));