复合主键的外键

Question

I have a problem with foreign keys.

The master table is:

Course (courseName, courseId) 

and PK is courseId

The second table is:

Section (sectionId, courseId) 

and PK is (sectionId, courseID) , FK is courseID reference Course(courseId)

And the problem table is:

GradeReport (studentId, sectionId, courseId, grade) 

and PK is (studentID, sectionID, courseID)

The FK's are

• courseId reference Course(courseID)
• sectionId reference Section(sectionID)

( no permisson for (courseId, sectionId) reference Section(courseId, sectionID))

The first FK is OK! But the second one gives me an error:

ORA-02270: no matching unique or primary key for this column-list

How can I solve this problem?

Answer 1

Since the primary key of Section is (sectionId, courseID), the foreign key constraint of GradeReport must be (sectionID, courseID).

In fact you will not need a foreign key constraint on GradeReport referencing Course, since the courseID will be in this foreign key constraint.

Answer 2

I don't understand the question fully, but if I had these tables my foreign keys would be:

• Section (which I think is OK for you already)

   FOREIGN KEY ..name.. REFERENCES Course(CourseID) 

• GradeReport (which is where I think you have the problem)

   FOREIGN KEY ..name.. REFERENCES Section(SectionID, CourseID) 

You don't need a separate Foreign Key for GradeReport.CourseID because it's already part of the SectionID, CourseID foreign key to Section , and Section.CourseID can be trusted because of the Section table's foreign key with Course .