Can't add foreign key to mysql

Question

I have multiple tables and they all seem to be fine but there is this one table which I'm trying to create but it wont work because I am keep on getting Error1005 "Foreign key constraint is incorrectly formed" .

These are the two tables. I don't know what seems to be the problem.

CREATE TABLE Patient(             
ID INT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE,
Name VARCHAR(255) NOT NULL, 
Age TINYINT UNSIGNED,
Sex VARCHAR(10),
Contact INT(11),
Email TEXT(2083), 
PRIMARY KEY(ID) 
);


CREATE TABLE Appointments (
Appointment_No INT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE,
Name VARCHAR(255) NOT NULL,
Contact INT(11),
Date DATE NOT NULL,
Time TIME NOT NULL,
Reason TEXT(2083), 
PRIMARY KEY(Appointment_No),
FOREIGN KEY (Name, Contact) REFERENCES Patient (Name, Contact)

); 

Answer 1

As per me, table structure should be like below:

CREATE TABLE Patient(             
ID INT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE,
Name VARCHAR(255) NOT NULL, 
Age TINYINT UNSIGNED,
Sex VARCHAR(10),
Contact INT(11),
Email TEXT(2083), 
PRIMARY KEY(ID) 
);

CREATE TABLE Appointments (
Appointment_No INT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE,
Patient_ID INT UNSIGNED NOT NULL,
Date DATE NOT NULL,
Time TIME NOT NULL,
Reason TEXT(2083), 
PRIMARY KEY(Appointment_No),
FOREIGN KEY (Patient_ID) REFERENCES Patient (ID)

); 

Answer 2

FOREIGN KEY (Name, Contact) REFERENCES Patient (Name, Contact)

The referenced columns in the Patient table must be part of a key. Ideally you would want Patient (Name, Contact) to be a unique key, because then the foreign key is guaranteed to reference exactly one row in the Patient table.

But in your table definition, the Name and Contact columns are not part of a key. That explains why you got the error given your table design.

But your table design is not good. Name and Contact are not good choices as a unique key, because two people can share a name, and in theory you could even have two people with the same name with the same contact details (for example, the former boxer George Foreman named his five sons George).

@Shadow is correct that it's a better idea is to reference Patient(id) instead, because it's guaranteed to be unique already.

Answer 3

Try to split the two foreign keys in two lines like this:

FOREIGN KEY (Contact) REFERENCES Patient (Contact) 
FOREIGN KEY (Name) REFERENCES Patient (Name)

Answer 4

Define Engine so sql statement would end with ENGINE = MyISAM;

It should fix the issue.