一对一关系

Question

I'm having trouble with the relationships with MySQL. Could someone tell me if this is a one to one relationship (between account and guest).

CREATE TABlE IF NOT EXISTS account
(
accountID       INT UNSIGNED    NOT NULL COMMENT 'primary key',   
guestFK         INT UNSIGNED    NOT NULL COMMENT 'account linked to particular guest',
password        VARCHAR(20)     NOT NULL COMMENT 'password of guest account',
CONSTRAINT account_PK PRIMARY KEY (accountID), 
CONSTRAINT account_FK FOREIGN KEY (accountID) REFERENCES hotel.guest(guestID)
);



CREATE TABLE IF NOT EXISTS guest
(
guestID     INT UNSIGNED    NOT NULL AUTO_INCREMENT  COMMENT 'primary key',
addressFK   INT UNSIGNED    NOT NULL COMMENT 'foreign key of guest address',
vehicleFK   INT UNSIGNED             COMMENT 'foreign key of guest vehicle',

firstName   VARCHAR(50)     NOT NULL COMMENT 'first name of guest',
lastName    VARCHAR(50)     NOT NULL COMMENT 'last name of guest',
phoneNum    INT UNSIGNED    NOT NULL COMMENT 'phone number of guest',
eMail       VARCHAR(50)     NOT NULL COMMENT 'e-mail address of guest',

CONSTRAINT guest_PK PRIMARY KEY (guestID),
CONSTRAINT address_FK FOREIGN KEY (addressFK) REFERENCES hotel.address(addressID),
CONSTRAINT vehicle_FK FOREIGN KEY (vehicleFK) REFERENCES hotel.vehicle(vehicleID),
CONSTRAINT email_UQ UNIQUE (eMail) COMMENT 'no two guests should have the same e-mail address',
CONSTRAINT guest_UQ UNIQUE (firstName, lastName, phoneNum) COMMENT 'no two guests  should have same name and phone number' 
);

Answer 1

No it isnt. You failed to supply a constraint in the account table to the guest foreign key. As it stands I can have multiple accounts for the same guest.

Consider marking the guestFK as unique. This would also dictate that your relational model needs to be revisited as the guestFK could than serve as a primary key, which would remove the need for accountID.

In your guest table consider a composite key over the following fields:
Firstname,lastname,email,phone number

Also, ensure you aren't storing passwords and are really only storing salted hashes.

Answer 2

Almost... It's not need for the foreign key (accountFK) in guest table if you already have it connected with the account table by the guestFK. There are two ways you can do this:

1. You keep the foreign key (guestFK) in the account table and delete the foreign key (accountFK) from the guest table
2. You keep the foreign key (accountFK) in the guest table and delete the foreign key (guestFK) from the account table.

Answer 3

You have guestFK as a foreign key referencing the guest.guestID field. A foreign key relationship means that an Account can have many guests. SO in terms of DB design, the answer would be NO it isnt one-to-one.