在多个表中分配主键和外键

Question

I just started a class in Oracle SQL and we were given an assignment to create 3 entity and 2 relation tables. He gave us these fields and said add as we feel necessary:

Course: department, semester, maximumEnrolled
Instructor: firstName, lastName, ssn
Room: roomNumber, building
Teaches: instructor, course
Uses: course, room

When I created the tables, only the first 4 worked but I am not able to create the uses table. The error is:

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

This is what I did:

CREATE TABLE course
    (course_id NUMBER(4) PRIMARY KEY,
    courseName VARCHAR2(30) NOT NULL,
    department VARCHAR2(50),
    semester VARCHAR2(10),
    maximumEnrolled NUMBER(36) NOT NULL);

CREATE TABLE room
    (roomNo NUMBER(5) PRIMARY KEY,
    building VARCHAR2(10));

CREATE TABLE instructor
    (instructor_id NUMBER(6) PRIMARY KEY,
    firstName VARCHAR2(20),
    lastName VARCHAR2(30) NOT NULL
    ssn NUMBER(9) NOT NULL);

CREATE TABLE teaches
    (instructor_id NUMBER(5) NOT NULL,
    course_id NUMBER(4) NOT NULL,
    teachingCourse VARCHAR2(4) PRIMARY KEY, 
    CONSTRAINT instructor_fk FOREIGN KEY (instructor_id) REFERENCES instructor (instructor_id)
    CONSTRAINT course_fk FOREIGN KEY (course_id) REFERENCES course (course_id));

CREATE TABLE uses
    (course_id NUMBER(4) NOT NULL,
    roomNo NUMBER(5) NOT NULL,
    roomUse VARCHAR2(4) PRIMARY KEY,
    CONSTRAINT course_fk FOREIGN KEY (course_id) REFERENCES course (course_id)
    CONSTRAINT room_fk FOREIGN KEY (roomNo) REFERENCES room (roomNo));

I thought maybe the problem is that I used course_id as a FK in the teaches table so I tried:

CREATE TABLE uses
  (roomUsage VARCHAR2(30) PRIMARY KEY,
  roomNo NUMBER(5) NOT NULL,
  courseName VARCHAR2(30) NOT NULL,
  CONSTRAINT room_fk FOREIGN KEY (roomNo) REFERENCES room (roomNo),
  CONSTRAINT course_fk FOREIGN KEY (courseName) REFERENCES course (courseName));

But it didn't work either and gave the same error. What am I doing wrong?

Answer 1

There are some commas missing in some of your table definitions (after lastname in instructor , after the first fk in the two last tables) and also a data type mismatch (in size) for the instructor_id in teaches . Also, foreign key constraint names must be unique - you are reusing course_fk in the uses table - rename it.

The corrected code would be this:

CREATE TABLE course
    (course_id NUMBER(4) PRIMARY KEY,
    courseName VARCHAR2(30) NOT NULL,
    department VARCHAR2(50),
    semester VARCHAR2(10),
    maximumEnrolled NUMBER(36) NOT NULL
    );

CREATE TABLE room
    (roomNo NUMBER(5) PRIMARY KEY,
    building VARCHAR2(10));

CREATE TABLE instructor
    (instructor_id NUMBER(6) PRIMARY KEY,
    firstName VARCHAR2(20),
    lastName VARCHAR2(30) NOT NULL,
    ssn NUMBER(9) NOT NULL
    );

CREATE TABLE teaches
    (instructor_id NUMBER(6) NOT NULL,
    course_id NUMBER(4) NOT NULL,
    teachingCourse VARCHAR2(4) PRIMARY KEY, 
    CONSTRAINT instructor_fk FOREIGN KEY (instructor_id) REFERENCES instructor (instructor_id),
    CONSTRAINT course_fk FOREIGN KEY (course_id) REFERENCES course (course_id)
    );

CREATE TABLE uses
    (course_id NUMBER(4) NOT NULL,
    roomNo NUMBER(5) NOT NULL,
    roomUse VARCHAR2(4) PRIMARY KEY,
    CONSTRAINT course_fk2 FOREIGN KEY (course_id) REFERENCES course (course_id),
    CONSTRAINT room_fk FOREIGN KEY (roomNo) REFERENCES room (roomNo)
    );

Working SQL Fiddle