MySQL Set NULLABLE Unique Field

Question

I've a case where I need to store twitter username, email, and some other field to be unique. However, I can only set twitter username later. Not on registration process. How can I handle this in SQL?

Here's my current SQL structure:

CREATE TABLE `kios_users` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `username` varchar(32) NOT NULL,
 `password` varchar(60) NOT NULL,
 `email` varchar(100) NOT NULL,
 `no_hp` varchar(15) NOT NULL,
 `twitter_oauth_token` varchar(60) NOT NULL,
 `twitter_oauth_token_secret` varchar(60) NOT NULL,
 `twitter_username` varchar(32) NULL,
 `verify_level` enum('just_reg','hp_ok','all_ok') NOT NULL,
 PRIMARY KEY (`id`),
 UNIQUE KEY `email` (`email`),
 UNIQUE KEY `no_hp` (`no_hp`),
 UNIQUE KEY `username` (`username`),
 UNIQUE KEY `twitter_username` (`twitter_username`)
) ENGINE=MyISAM

With this kind of structure, I can't set twitter_username to empty. Can you suggest me the best table structure?

Answer 1

You could set a dummy unique value, but is not the best. You could manage uniqueness in the app logic, not the best. I think the best is to use another table with only two fields: id and twitter_username with a unique key on twitter_username and insert only when you have the twitter username. Also, there should be a one-to-one relationship on both id columns.

Answer 2

You've set twitter_username to be "NOT NULL". Try

`twitter_username` varchar(32) NULL

Answer 3

Could you not just allow NULL for your twitter params and enforce uniqueness at the application level? (ie. in php/.net/whatever you're using)

Alternatively, store the twitter account details in a separate table linked to your user id