MySQL - Unique foreign key

Question

I have to make one of the foreign keys unique. The problem is, I am getting the following message from the phpMyAdmin:

The following indexes appear to be equal an         


        

Answer 1

Just so you know, it seems like you can also have UNIQUE foreign keys:

CREATE TABLE user(
uid INT NOT NULL AUTO_INCREMENT,
username VARCHAR(16) NOT NULL UNIQUE,
email_id INT NOT NULL UNIQUE,
FOREIGN KEY (email_id) REFERENCES email(uid)
    ON DELETE CASCADE
    ON UPDATE CASCADE,

PRIMARY KEY (uid));