MySQL的：使用两个外键到同一个表

Question

I'm using MySQL workbench to design a database. Server is mysql 5.5.6

I've defined a few foreign keys linking the "candidates" table to the "countries" table. I get this error:

Executing SQL script in server
ERROR: Error 1005: Can't create table 'customer.candidats' (errno: 150)

The thing is: i'm referencing twice the countries table: once for the "nationality" column, once for the user address's country of origin. Is that allowed? Is this the right way to do it?

Here is the generated code that seems to trigger the issue.

CREATE TABLE IF NOT EXISTS `customer`.`candidats` (
  `id` INT NOT NULL AUTO_INCREMENT,
  `nom` VARCHAR(40) NULL,
  `prenom` VARCHAR(40) NULL,
  `qualite` ENUM('0001','0002') NULL COMMENT '0001 = Madame\n0002 = Monsieur',
  `sexe` SET('1','2') NULL COMMENT '1 = Femme\n2 = Homme',
  `date_de_naissance` DATE NULL,
  `Nationalite` INT NOT NULL,
  `selor_bilinguisme` TINYINT(1) NULL,
  `rue` VARCHAR(60) NULL,
  `numero` VARCHAR(10) NULL,
  `pays` INT NOT NULL,
  `region` INT NOT NULL,
  `localité` VARCHAR(40) NULL,
  `code_postal` VARCHAR(10) NULL,
  `email` VARCHAR(241) NULL,
  `tel_domicile` VARCHAR(30) NULL,
  `tel_bureau` VARCHAR(30) NULL,
  `tel_mobile` VARCHAR(30) NULL,
  `tel_prefere` ENUM('01','02','03') NULL DEFAULT '03',
  PRIMARY KEY (`id`),
  INDEX `fk_candidats_pays_idx` (`Nationalite` ASC, `pays` ASC),
  INDEX `fk_candidats_régions1_idx` (`region` ASC),
  CONSTRAINT `fk_candidats_pays`
    FOREIGN KEY (`Nationalite` , `pays`)
    REFERENCES `customer`.`pays` (`id` , `id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_candidats_régions1`
    FOREIGN KEY (`region`)
    REFERENCES `customer`.`régions` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB

The "pays" table ("countries" in French)

CREATE TABLE IF NOT EXISTS `customer`.`pays` (
  `id` INT NOT NULL AUTO_INCREMENT,
  `nom_fr` VARCHAR(45) NULL,
  `nom_nl` VARCHAR(45) NULL,
  `nationalite_fr` VARCHAR(45) NULL,
  `nationalite_nl` VARCHAR(45) NULL,
  PRIMARY KEY (`id`),
  UNIQUE INDEX `id_UNIQUE` (`id` ASC))
ENGINE = InnoDB

Answer 1

Your schema generator doesn't work correctly.

It should generate:

CONSTRAINT `fk_candidats_pays`
    FOREIGN KEY (`pays`)
    REFERENCES `customer`.`pays` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
CONSTRAINT `fk_candidats_Nationalite`
    FOREIGN KEY (`Nationalite`)
    REFERENCES `customer`.`pays` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,

To your other question: This type of referencing seems strange when you see it the first time, but it's quite normal and I think there is no other way of constructing this type of relationship.