多项选择题的数据库结构

Question

I am developing a demo application for an online multiple choice examination. Each question will have multiple options, of course. On the question screen, candidate will select one of the option, submit it and will be navigated to the next question.

I have worked out following table structure.

CREATE  TABLE users (
  username VARCHAR(45) NOT NULL ,
  password VARCHAR(45) NOT NULL ,
  enabled TINYINT NOT NULL DEFAULT 1 ,
);

CREATE TABLE questions (
    id int(10) NOT NULL auto_increment
    question varchar(800) NOT NULL,
    right_option int(10) NOT NULL references options(id)
);

CREATE TABLE options (
    id int(10) NOT NULL auto_increment,  
    question_id int(10) NOT NULL references questions(id),
    option varchar(150) NOT NULL,              
);

CREATE TABLE exam_details (
    id  int(10) NOT NULL,
    username varchar(45) NOT NULL references users(username),
    date_of_exam date,
    exam_result varchar(10) NOT NULL, -- PASS/FAIL
    exam_score int(10) NOT NULL,      -- e.g. 40 
    no_of_questions int(10) NOT NULL  -- total no. of questions in the test
);     

CREATE TABLE user_answers (
    id  int(10) NOT NULL,
    username varchar(45) NOT NULL references users(username),
    question_id int(10) NOT NULL references questions(id),
    answer int(10) NOT NULL references options(id)
 );

The database will be MySql. But please ignore the syntax since i just want to convey the idea. Please suggest if there can be a better approach.
Just to add I will be using spring & hibernate on the server side.

Answer 1

Once you clean things up a bit, biggest one being the user_answers.username (which is de-normalized), by trying something like this:

CREATE  TABLE users (
  id int(10) auto_increment primary key,
  username VARCHAR(45) NOT NULL ,
  password VARCHAR(45) NOT NULL ,
  enabled TINYINT NOT NULL DEFAULT 1
);

CREATE TABLE questions (
    id int(10) auto_increment primary key,
    question varchar(800) NOT NULL,
    right_option int(10) NOT NULL references options(id)
);

CREATE TABLE options (
    id int(10) auto_increment primary key,
    question_id int(10) NOT NULL references questions(id),
    `option` varchar(150) NOT NULL
);

CREATE TABLE exam_details (
    id int(10) auto_increment primary key,
    username varchar(45) NOT NULL references users(username),
    date_of_exam date not null,
    exam_result varchar(10) NOT NULL, -- PASS/FAIL
    exam_score int(10) NOT NULL,      -- e.g. 40 
    no_of_questions int(10) NOT NULL  -- total no. of questions in the test
);     

CREATE TABLE user_answers (
    id int(10) auto_increment primary key,
    userId int(10) NOT NULL references users(id),
    question_id int(10) NOT NULL references questions(id),
    answer int(10) NOT NULL references options(id)
);

Then the only problem that immediately jumps out at me is that the user_answers.answer could technically be saved as an answer to a different question.

The biggest takeaway for you is to never do that with the username in the answers table. Can't have more than one real user with the same name that way (big problem). Also, if the user name was a typo, it changes in one place in users table. Data integrity. Join on an id as such.

Note: an auto_increment must be a primary key, and a primary key can never be NULL, so it is redundant to type NOT NULL next to it. Just saying.

Answer 2

I recently had the need to write a questionnaire system that was fully database driven and changeable by the client.

I ended up storing the possible answers as a JSON object in the database and then storing the answer given against the question ID, however this adds a few levels of complexity.

If every question is a multi-choice answer then your approach would be a logical approach