Error 1005 (HY000): Can't create table db.Wine (errno: 150) - mysql

Question

I have this code to create some tables:
CREATE TABLE Appelations (
No int AUTO_INCREMENT,
Appelation varchar(35),
County varchar(20),
State varchar(15),
Area varchar(25),
IsAVA varchar(3),
PRIMARY KEY (No)
);
CREATE TABLE Grapes (
ID int AUTO_INCREMENT,
Grape varchar(25),
Color varchar(10),
PRIMARY KEY (ID)
);
CREATE TABLE Wine (
No int AUTO_INCREMENT,
Grape varchar(25),
Winery varchar(40),
Appelation varchar(35),
Name varchar(40),
Year year,
Price int,
Score int,
Cases int,
PRIMARY KEY (No),
FOREIGN KEY (Grape) REFERENCES Grapes(Grape),
FOREIGN KEY (Appelation) REFERENCES Appelations(Appelation)
);
But when I run it, I get this error:
ERROR 1005 (HY000): Can't create table 'db.Wine' (errno: 150)
Does anyone know how to fix this? Thanks.

Answer 1

You need indexes on your foreign keys: "MySQL requires indexes on foreign keys and referenced keys so that foreign key checks can be fast and not require a table scan."
Example here: http://sqlfiddle.com/#!9/d228b8
CREATE TABLE Appelations (
No int AUTO_INCREMENT,
Appelation varchar(35),
County varchar(20),
State varchar(15),
Area varchar(25),
IsAVA varchar(3),
INDEX appelation_ind (Appelation), /*<---*/
PRIMARY KEY (No)
);
CREATE TABLE Grapes (
ID int AUTO_INCREMENT,
Grape varchar(25),
Color varchar(10),
INDEX grape_ind (Grape), /*<---*/
PRIMARY KEY (ID)
);
CREATE TABLE Wine (
No int AUTO_INCREMENT,
Grape varchar(25),
Winery varchar(40),
Appelation varchar(35),
Name varchar(40),
Year year,
Price int,
Score int,
Cases int,
PRIMARY KEY (No),
FOREIGN KEY (Grape) REFERENCES Grapes(Grape),
FOREIGN KEY (Appelation) REFERENCES Appelations(Appelation)
);

Answer 2

That's because the FOREIGH KEY columns in the table are referencing the columns that are neither primary keys nor have indexes on them (in parent tables). You can change the type and make them point to ID and No columns of Grapes and Appelations tables respectively, e.g.:
CREATE TABLE Wine (
No int AUTO_INCREMENT,
Grape_id int,
Winery varchar(40),
Appelation_no int,
Name varchar(40),
Year year,
Price int,
Score int,
Cases int,
PRIMARY KEY (No),
FOREIGN KEY (Grape_id) REFERENCES Grapes(id),
FOREIGN KEY (Appelation_no) REFERENCES Appelations(No)
);
Here's the SQL Fiddle.