Question

I’m not sure why these have to be unique, but from reading the MySQL forums it appears that they do. However, I think it has something more to do with the INDEX name. I have two tables that have foreign key constraints referencing the same primary key on a third table. If it helps, I’m using MySQL workbench to design the schema.

I usually name my foreign key on each table the same name as the primary key it references. I guess this isn’t possible. It will create the first table with the foreign key constraint, but when it tries to create the second table it throws an error. Here is the second table it throws the error on:

CREATE  TABLE IF NOT EXISTS `joe`.`products_to_categories` (
  `product_to_category_id` INT NOT NULL AUTO_INCREMENT ,
  `category_id` INT NOT NULL ,
  `product_id` INT NOT NULL ,
  PRIMARY KEY (`product_to_category_id`) ,
  INDEX `category_id` (`category_id` ASC) ,
  INDEX `product_id` (`product_id` ASC) ,
  CONSTRAINT `category_id`
    FOREIGN KEY (`category_id` )
    REFERENCES `joe`.`categories` (`category_id` )
    ON DELETE CASCADE
    ON UPDATE NO ACTION,
  CONSTRAINT `product_id`
    FOREIGN KEY (`product_id` )
    REFERENCES `joe`.`products` (`product_id` )
    ON DELETE CASCADE
    ON UPDATE NO ACTION)
ENGINE = InnoDB;

I want the foreign key names to be the same as the primary key in both of the other tables. What should I remove here so that I can use these names. What is the best practice here.

Answer 1

It is not possible because you would have a conflict in the filename for the file that is used for the index IIRC. I probably would name the key < tablename >_< column_name > or something like that.