Need help understanding this SQL (generated by doctrine)

i am actually reading Doctrine Reference: One to Many, Unidirectional with Join table. but this will probably be more of a SQL quesiton. basically, this is supposed to model a one to many, unidirectional relationship. i guess from the PHP code (in that link), its such that 1 user have many phonenumbers.

the question is from the SQL, it seems like 1 user can have many phonenumbers. and 1 phonenumber can only belong to 1 user. am i right?

CREATE TABLE User (
    id INT AUTO_INCREMENT NOT NULL,
    PRIMARY KEY(id)
) ENGINE = InnoDB;

CREATE TABLE users_phonenumbers (
    user_id INT NOT NULL,
    phonenumber_id INT NOT NULL,
    UNIQUE INDEX users_phonenumbers_phonenumber_id_uniq (phonenumber_id),
    PRIMARY KEY(user_id, 
phonenumber_id)
) ENGINE = InnoDB;

CREATE TABLE Phonenumber (
    id INT AUTO_INCREMENT NOT NULL,
    PRIMARY KEY(id)
) ENGINE = InnoDB;

ALTER TABLE use开发者_如何学Crs_phonenumbers ADD FOREIGN KEY (user_id) REFERENCES User(id);
ALTER TABLE users_phonenumbers ADD FOREIGN KEY (phonenumber_id) REFERENCES Phonenumber(id);

can't i just simplify the database to ... below ... no need for join tables and what not?

Users (id, name)
Phonenumbers (id, user [FK], number)

Correct, these are two valid approaches to the same problem. And yes, the unique index on users_phonenumbers means that each phone number can belong to only one user.

The design is actually suboptimal.

The idea must have been that there are telephone numbers, users, and that they can be linked many-to-many. Because of the unique index on phonenumberid hoever, each number can only be assigned to one user.

Then the whole users_phonenumbers has become redundant, because they could just have added a userid column on the phonenumbers table and save themselves a join.

BAd table design if you ask me.