Question

I want to limit the datatype value that can be stored within a field to a specific range of integer values: [0,10].

On user input within a PHP script I validate and sanitise the data to make sure it is within the range 0 to 10. However, is there a way to ensure this remains true within the votes table itself via some sort of datatype or constraint?

At the moment I store the int value within an UNSIGNED TINYINT which of course has the range of 0-255. I am aware of ENUM as an option. However, I have read that it is not advisable when using numbers: http://komlenic.com/244/8-reasons-why-mysqls-enum-data-type-is-evil/

The SQL:

CREATE TABLE votes (
vote_id MEDIUMINT UNSIGNED NOT NULL AUTO_INCREMENT,
article_id MEDIUMINT UNSIGNED NOT NULL,
user_id MEDIUMINT UNSIGNED NOT NULL,
user_vote TINYINT UNSIGNED NOT NULL,
PRIMARY KEY (vote_id),
FOREIGN KEY (article_id) REFERENCES articles (article_id) ON DELETE CASCADE ON UPDATE NO ACTION,
FOREIGN KEY (user_id) REFERENCES users (user_id) ON DELETE CASCADE ON UPDATE NO ACTION,
CONSTRAINT article_uservoted UNIQUE KEY (user_id, article_id),
INDEX vote_value (article_id, user_id, user_vote)
) ENGINE=INNODB;

I hope someone can assist.

Answer 1

You can create a table of allowed vote values and add a foreign key in your votes table, so when you try to insert a vote with user_vote value other than existing in your allowed_votes table you get a constraint fail error:

CREATE TABLE allowed_votes (
  vote_rank TINYINT UNSIGNED NOT NULL,
  PRIMARY KEY (vote_rank)
) ENGINE = InnoDB;

INSERT INTO allowed_votes( vote_rank ) VALUES(1),(2),(3),(4),(5),(6),(7),(8),(9),(10);

ALTER TABLE votes
ADD FOREIGN KEY (user_vote) REFERENCES allowed_votes (vote_rank);