Question

I have two tables as follows:

CREATE TABLE customer
(
  id INT NOT NULL AUTO_INCREMENT,
  name VARCHAR(25),
  PRIMARY KEY(id)
);

CREATE TABLE `client`
(
  `id` INT NOT NULL AUTO_INCREMENT,
  `name` VARCHAR(200),
  `customer_id` INT NOT NULL,

   PRIMARY KEY(`id`),
   INDEX(`customer_id`),
   FOREIGN KEY (`customer_id`) REFERENCES `customer`(`id`) ON UPDATE CASCADE ON DELETE RESTRICT
);

Then I ran the following:

INSERT INTO customer (name) VALUES ('Customer1');

Now the table customer contains name: Customer1, id: 1

Then I ran this:

INSERT INTO client (name, customer_id) VALUES ('Client of Customer1',34);

It was supposed to fail, but it inserted successfully. Why is that?

This is on MySQL 5.1 on Linux Mint.

Answer 1

Do a show create table customer. It’ll show the engine used at the end of the dumped create table statement. If they’re showing as MyISAM, that engine doesn’t suport foreign keys. The FK definitions are parsed, but otherwise ignored.

To force a table to be Inno DB, which DOES support foren keys, you have to do

CREATE TABLE ( ... blah blah blah ...) TYPE=InnoDB;
                                       ^^^^^^^^^^^--force InnoDB type