SQL> CREATE TABLE Course_Enrollment
  2  (
  3   Student_ID char(8) NOT NULL,
  4   Course_ID char(10) NOT NULL,
  5   Year_enrolled char(4) NOT NULL,
  6   Semester Integer NOT NULL,
  7   Grade Integer DEFAULT NULL,
  8   PRIMARY KEY(Student_ID,Course_ID, Year_enrolled, Semester),
  9   FOREIGN KEY(Student_ID) REFERENCES Student(Student_ID) ON UPDATE CASCADE
 10   FOREIGN KEY(Course_ID) REFERENCES Course(Course_ID) ON UPDATE CASCADE
 11   CONSTRAINT GradeCheck CHECK (Grade IN (1,2,3,4,5,6,7))
 12  );
 FOREIGN KEY(Student_ID) REFERENCES Student(Student_ID) ON UPDATE CASCADE
                                                           *
ERROR at line 9:
ORA-00905: missing keyword