MySQL Foreign Key, Can't create table (errno: 150)

Question

I am trying to build the database and tables for my system. But I found that if I don't add the foreign key in the codes. There is no error. I've used many method try to make the codes works, but it still have error.

I am using MySQL 5.5.31, and the codes here: CREATE DATABASE TOS;

DROP TABLE TOS.USER CASCADE;
DROP TABLE TOS.BILL_HEADER CASCADE;
DROP TABLE TOS.TOY CASCADE;


CREATE TABLE TOS.USER
(User Char(8),
Name Char(10),
Type Char(1),
Password Char(12),
PRIMARY KEY(User));

CREATE TABLE TOS.BILL_HEADER
(Bill_No Char(10),
CTime DateTime,
No_Of INTEGER,
Cus_No Char(5),
DTime DateTime,
PRIMARY KEY(Bill_No));

CREATE TABLE TOS.TOY
(Toy_Id Char(10),
FullN Char(50),
ShortN Char(20),
Descrip Char(20),
Price DECIMAL,
Avail Char(1),
Cat Char(1),
PRIMARY KEY(Toy_Id));

CREATE TABLE TOS.BILL_ITEM
(Bill_No Char(10),
BSeq_No INTEGER,
Toy_Id Char(10),
OTime DateTime,
Quan INT,
DCondition Char(1),
PRIMARY KEY(Bill_No,BSeq_No),
FOREIGN KEY(Bill_No) REFERENCES TOS.Bill_Header(Bill_No),
FOREIGN KEY(Toy_Id) REFERENCES TOS.TOY(Toy_Id));

Error:

1005 - Can't create table 'TOS.BILL_ITEM' (errno: 150)

Any help would be greatly appreciated.

Answer 1

The non-descript error 150 is usually related to foreign key data type or length mismatches, or a missing index on the parent table's column.

This look s to be a matter of case sensitivity in the table name Bill_Header (should be BILL_HEADER).
From the MySQL docs on identifier case sensitivity:

In MySQL, databases correspond to directories within the data directory. Each table within a database corresponds to at least one file within the database directory (and possibly more, depending on the storage engine). Consequently, the case sensitivity of the underlying operating system plays a part in the case sensitivity of database and table names. This means database and table names are not case sensitive in Windows, and case sensitive in most varieties of Unix.

Fix the case and it should work:

CREATE TABLE TOS.BILL_ITEM
(Bill_No Char(10),
BSeq_No INTEGER,
Toy_Id Char(10),
OTime DateTime,
Quan INT,
DCondition Char(1),
PRIMARY KEY(Bill_No,BSeq_No),
FOREIGN KEY(Bill_No) REFERENCES TOS.BILL_HEADER(Bill_No),
# Here-----------------------------^^^^^^^^^^^^^^
FOREIGN KEY(Toy_Id) REFERENCES TOS.TOY(Toy_Id));

Since your code worked as is at SQLFiddle.com (http://sqlfiddle.com/#!2/08d1e) the underlying platform there must not be case-sensitive.

Answer 2

Above answer is correct, but this error can also happen if the table your foreign key is referencing is MyISAM instead of innoDB.