Unable to relate two MySQL tables (foreign keys)

Question

Here is my USER table

CREATE TABLE IF NOT EXISTS `users` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `username` varchar(100) NOT NULL,
  `expiry` varchar(6) NOT NULL,
  `contact_id` int(11) NOT NULL,
  `email` varchar(255) NOT NULL,
  `password` varchar(100) NOT NULL,
  `level` int(3) NOT NULL,
  `active` tinyint(4) NOT NULL DEFAULT '1',
  PRIMARY KEY (`id`,`email`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;

And here is my contact_info table

CREATE TABLE IF NOT EXISTS `contact_info` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) NOT NULL,
  `email_address` varchar(255) NOT NULL,
  `company_name` varchar(255) NOT NULL,
  `license_number` varchar(255) NOT NULL,
  `phone` varchar(30) NOT NULL,
  `fax` varchar(30) NOT NULL,
  `mobile` varchar(30) NOT NULL,
  `category` varchar(100) NOT NULL,
  `country` varchar(20) NOT NULL,
  `state` varchar(20) NOT NULL,
  `city` varchar(100) NOT NULL,
  `postcode` varchar(50) NOT NULL,
  PRIMARY KEY (`id`,`email_address`),
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;

The system uses username to login users. I want to modify it in such a way that it uses email for login. But there is no email_address in users table.

I have added foreign key - email in user table(which is email_address in contact_info).

How should I query database?

Do you really want to have two email addresses for each user? Or is it a one to many relation between the two tables? — 2ndkauboy

paxdiablo paxdiablo · Accepted Answer · 2010-06-13T13:21:28

No, no, no, no no. Seriously, no. Don't make me come over there :-)

You're breaking third normal form by storing the email address twice.

The relationship need only be a short one, that of id. Assuming you're not guaranteeing the IDs will be identical in the two tables (i.e., my users.id isn't necessarily equal to my contact_info.id), just add a ci_id to the users table to act as a foreign key to the contact_info table.

Then the query to get a user's username and email will be something like:

select u.username, ci.email
from users u, contact_info ci
where u.username = 'paxdiablo'
and u.ci_id = ci.id;

Unable to relate two MySQL tables (foreign keys)

1 Answers