error 1215 MYSQL Cannot add foreign key constraint,

问题

I have this code:

CREATE  TABLE IF NOT EXISTS `biblioteca`.`ejemplar` (

  `idejemplar` INT(11) NOT NULL AUTO_INCREMENT ,

  `estado` VARCHAR(45) NOT NULL ,

  `comentario` VARCHAR(45) NULL ,

  `isbn` VARCHAR(45) NOT NULL ,

  PRIMARY KEY (`idejemplar`) ,

  INDEX `fk_ejemplar_libro1_idx` (`isbn` ASC) ,

  CONSTRAINT `fk_ejemplar_libro1`

    FOREIGN KEY (`isbn` )

    REFERENCES `biblioteca`.`libro` (`isbn` )

    ON DELETE NO ACTION

    ON UPDATE NO ACTION)

ENGINE = InnoDB

DEFAULT CHARACTER SET = utf8

and the table that's makes reference is:

CREATE  TABLE IF NOT EXISTS `biblioteca`.`libro` (
  `isbn` VARCHAR(25) NOT NULL ,
  `idcategoria` INT(11) NOT NULL ,
  `ideditorial` INT(11) NOT NULL ,
  `titulo` VARCHAR(45) NOT NULL ,
  `autor` VARCHAR(45) NOT NULL ,
  `reseÃ±a` VARCHAR(45) NULL ,
  PRIMARY KEY (`isbn`) ,
  INDEX `fk_libro2_idx` (`idcategoria` ASC) ,
  INDEX `fk_libro3_idx` (`ideditorial` ASC) ,
  CONSTRAINT `fk_libro2`
    FOREIGN KEY (`idcategoria` )
    REFERENCES `biblioteca`.`categoria` (`idcategoria` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_libro3`
    FOREIGN KEY (`ideditorial` )
    REFERENCES `biblioteca`.`editorial` (`ideditorial` )
    ON DELETE CASCADE
    ON UPDATE CASCADE)
ENGINE = InnoDB
DEFAULT CHARACTER SET = utf8;

and i think thats foreign keys are good.

回答1:

If these are fresh tables with no values, It seems like an error with the columns

one has a varchar(25) the other a var_char(45) make them the same

edit:

CREATE  TABLE IF NOT EXISTS `biblioteca`.`libro` (
  `isbn` VARCHAR(45) NOT NULL ,
  `idcategoria` INT(11) NOT NULL ,
  `ideditorial` INT(11) NOT NULL ,
  `titulo` VARCHAR(45) NOT NULL ,
  `autor` VARCHAR(45) NOT NULL ,
  `reseÃ±a` VARCHAR(45) NULL ,
  PRIMARY KEY (`isbn`) ,
  INDEX `fk_libro2_idx` (`idcategoria` ASC) ,
  INDEX `fk_libro3_idx` (`ideditorial` ASC) )

ENGINE = INNODB
DEFAULT CHARACTER SET = utf8;



CREATE  TABLE IF NOT EXISTS `biblioteca`.`ejemplar` (

  `idejemplar` INT(11) NOT NULL AUTO_INCREMENT ,

  `estado` VARCHAR(45) NOT NULL ,

  `comentario` VARCHAR(45) NULL ,

  `isbn` VARCHAR(45) NOT NULL ,

  PRIMARY KEY (`idejemplar`) ,

  INDEX `fk_ejemplar_libro1_idx` (`isbn` ASC) ,

  CONSTRAINT `fk_ejemplar_libro1`

    FOREIGN KEY (`isbn` )

    REFERENCES `biblioteca`.`libro` (`isbn` )

    ON DELETE NO ACTION

    ON UPDATE NO ACTION)

ENGINE = INNODB

DEFAULT CHARACTER SET = utf8;

works no problem for me. Ive taken away the other 2 keys which i dont have schemas for though

来源：https://stackoverflow.com/questions/17532926/error-1215-mysql-cannot-add-foreign-key-constraint

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