Foreign keys referring other foreign keys in PostgreSQL

Question

In PostgreSQL I have a database, which I intend to make the following table declaration:

CREATE TABLE canvas_user (
    id INTEGER,
    login_id VARCHAR(50) UNIQ         


        

Answer 1

Make the foreign key from the correction table to the submission table a compound key that is unique. Also, review the design of the submission table; num is a serial type and should be the unique primary key. You can add a unique constraint to the columns num, user_id, and assignment_id

CREATE TABLE canvas_user (
    id INTEGER,
    login_id VARCHAR(50) UNIQUE NOT NULL,
    email VARCHAR(355) UNIQUE NOT NULL,
    name_given VARCHAR(30),
    name_family VARCHAR(30),
    name_full VARCHAR(50),
    role canvas_role,
    last_login TIMESTAMP,
    PRIMARY KEY (id)
);


CREATE TABLE problem (
    id SERIAL,
    title VARCHAR(50),
    author VARCHAR(50),
    path TEXT,
    compiler VARCHAR(20),
    PRIMARY KEY (id)
);


CREATE TABLE assignment (
    id INTEGER,
    title TEXT NOT NULL,
    points_possible INTEGER NOT NULL,
    problem_id INTEGER,
    PRIMARY KEY (id),
    FOREIGN KEY (problem_id) REFERENCES problem(id)
);


CREATE TABLE submission (
    num SERIAL,
    user_id INTEGER,
    assignment_id INTEGER,
    timestamp TIMESTAMP,
    path TEXT,
    lti_info TEXT[],
    PRIMARY KEY(num, user_id, assignment_id),
    FOREIGN KEY (user_id) REFERENCES canvas_user(id),
    FOREIGN KEY (assignment_id) REFERENCES assignment(id)
);


CREATE TABLE correction (
    num INTEGER,
    user_id INTEGER,
    assignment_id INTEGER,
    timestamp TIMESTAMP,
    path TEXT,
    execution_time interval,
    PRIMARY KEY(num, user_id, assignment_id),
    FOREIGN KEY (num, user_id,assignment_id ) REFERENCES submission(num, user_id, assignment_id)

);