Question

Doing my first tryouts with foreign keys in a mySQL database and are trying to do a insert, that fails for this reason: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails

Does this mean that foreign keys restrict INSERTS as well as DELETES and/or UPDATES on each table that is enforced with foreign keys relations?

Thanks!

Updated description:

Products
----------------------------
id    | type
----------------------------
0     | 0
1     | 3

ProductsToCategories
----------------------------
productid | categoryid
----------------------------
0         | 0
1         | 1

Product table has following structure

CREATE  TABLE IF NOT EXISTS `alpha`.`products` (
  `id` MEDIUMINT UNSIGNED NOT NULL AUTO_INCREMENT ,
  `type` TINYINT(2) UNSIGNED NOT NULL DEFAULT 0 ,    
  PRIMARY KEY (`id`) ,  
  CONSTRAINT `funkyfunky`  
    FOREIGN KEY (`id` )
    REFERENCES `alpha`.`ProductsToCategories` (`productid` )    
    ON DELETE CASCADE,    
    ON UPDATE CASCADE)  

ENGINE = InnoDB;

Answer 1

Your products table is slightly wrong, as you don’t need to reference anything from it. References go in the “other” tables, and point to the main, e.g:

create table products (
  id int auto_increment,
  type int,
  primary key (id)
);

create table categories (
  id int auto_increment,
  name varchar(128),
  primary key (id)
)

create table products_to_categories (
  product_id int references products,
  category_id int references categories
);