CREATE TABLE students(
    id SERIAL PRIMARY KEY,
    student_name VARCHAR(20)
);

CREATE TABLE exams(
    id INTEGER GENERATED ALWAYS AS IDENTITY (START WITH 101 INCREMENT 1) PRIMARY KEY,
    exam_name VARCHAR(20)
);

CREATE TABLE study_halls(
    id SERIAL PRIMARY KEY,
    study_hall_name VARCHAR(30),
    exam_id INTEGER,

    CONSTRAINT fk_study_halls_exams
    FOREIGN KEY (exam_id)
    REFERENCES exams(id)
);


CREATE TABLE students_exams(
    student_id INT,
    exam_id INT,

    CONSTRAINT pk_students_exams
    PRIMARY KEY (student_id, exam_id),
    
    CONSTRAINT fk_students_exams_students
    FOREIGN KEY (student_id)
    REFERENCES students(id),

    CONSTRAINT fk_students_exams_exams
    FOREIGN KEY (exam_id)
    REFERENCES exams(id)

);

INSERT INTO students(student_name)
VALUES
    ('Mila'),
    ('Toni'),
    ('Ron');

INSERT INTO exams(exam_name)
VALUES
    ('Python Advanced'),
    ('Python OOP'),
    ('PostgreSQL');

INSERT INTO study_halls(study_hall_name, exam_id)
VALUES
    ('Open Source Hall', 102),
    ('Inspiration Hall', 101),
    ('Creative Hall', 103),
    ('Masterclass Hall', 103),
    ('Information Security Hall', 103);

INSERT INTO students_exams
VALUES 
    (1, 101),
    (1, 102),
    (2, 101),
    (3, 103), 
    (2, 102),
    (2, 103);