title: ora-02270 How do i fix this?
body: <p>This is what I have: </p>
  
  <pre><code>CREATE TABLE STUDENTS(
      stu_id NUMBER(9) NOT NULL,
      stu_name VARCHAR2(15) NOT NULL,
      stu_address VARCHAR2(15),
      stu_major VARCHAR2(6),
      CONSTRAINT students_pk PRIMARY KEY (stu_id)
  );
  
  
  CREATE TABLE GRADE(
      stu_id NUMBER(9) NOT NULL,
      course_id VARCHAR2(7),
      stu_crse_grade VARCHAR2(1),
      PRIMARY KEY (stu_id, course_id),
      FOREIGN KEY (stu_id) REFERENCES students(stu_id),
      CHECK (stu_crse_grade = 'A' 
      AND stu_crse_grade = 'B' 
      AND stu_crse_grade = 'C' 
      AND stu_crse_grade = 'D' 
      AND stu_crse_grade = 'F')
  );
  
  
  CREATE TABLE COURSE(
      course_id VARCHAR2(7),
      course_title VARCHAR2(20),
      instructor_id NUMBER(3),
      PRIMARY KEY (course_id, instructor_id),
      FOREIGN KEY (course_id) REFERENCES grade(course_id)
  );
  </code></pre>
  
  <p>When I try to create the 3rd table I get this error. Is it because of the composite primary key in the grade table? How do I fix this?</p>