MySQL innodb - Foreign Key: only 1st works? - mysql

Question

I have this example bellow where customers_b cannot be created.
Error Code 1005 / errno: 121.
However, if I create customers_b first than customers_a, then customers_a is the one which won't be created.
What is wrong? Why I cant link more than one FK to the PK 'id_state'?
Thanks!
SET #OLD_UNIQUE_CHECKS=##UNIQUE_CHECKS, UNIQUE_CHECKS=0;
SET #OLD_FOREIGN_KEY_CHECKS=##FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0;
SET #OLD_SQL_MODE=##SQL_MODE, SQL_MODE='TRADITIONAL,ALLOW_INVALID_DATES';
DROP SCHEMA IF EXISTS `testdb` ;
CREATE SCHEMA IF NOT EXISTS `testdb` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci ;
USE `testdb` ;
-- -----------------------------------------------------
-- Table `testdb`.`state`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `testdb`.`state` ;
CREATE TABLE IF NOT EXISTS `testdb`.`state` (
`id_state` INT NOT NULL,
`abbr` CHAR(2) NOT NULL,
PRIMARY KEY (`id_state`),
UNIQUE INDEX `id_state_UNIQUE` (`id_state` ASC))
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `testdb`.`customers_a`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `testdb`.`customers_a` ;
CREATE TABLE IF NOT EXISTS `testdb`.`customers_a` (
`id_customer` INT NOT NULL AUTO_INCREMENT,
`name` VARCHAR(45) NOT NULL,
`addr_state` INT NOT NULL,
PRIMARY KEY (`id_customer`),
CONSTRAINT `fk_state`
FOREIGN KEY (`addr_state`)
REFERENCES `testdb`.`state` (`id_state`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `testdb`.`customers_b`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `testdb`.`customers_b` ;
CREATE TABLE IF NOT EXISTS `testdb`.`customers_b` (
`id_customer` INT NOT NULL AUTO_INCREMENT,
`name` VARCHAR(45) NOT NULL,
`addr_state` INT NOT NULL,
PRIMARY KEY (`id_customer`),
CONSTRAINT `fk_state`
FOREIGN KEY (`addr_state`)
REFERENCES `testdb`.`state` (`id_state`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;

Answer 1

You can't use the same name fk_state for both constraints. Give one of them a different name.
CREATE TABLE IF NOT EXISTS `customers_b` (
`id_customer` INT NOT NULL AUTO_INCREMENT,
`name` VARCHAR(45) NOT NULL,
`addr_state` INT NOT NULL,
PRIMARY KEY (`id_customer`),
CONSTRAINT `fk_state_b`
FOREIGN KEY (`addr_state`)
REFERENCES `state` (`id_state`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;

Answer 2

Your both tables constraint name is same CONSTRAINT fk_state. for customer_b change that name like below
CREATE TABLE IF NOT EXISTS `customers_a` (
`id_customer` INT NOT NULL AUTO_INCREMENT,
`name` VARCHAR(45) NOT NULL,
`addr_state` INT NOT NULL,
PRIMARY KEY (`id_customer`),
CONSTRAINT `fk_state`
FOREIGN KEY (`addr_state`)
REFERENCES `state` (`id_state`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
CREATE TABLE IF NOT EXISTS `customers_b` (
`id_customer` INT NOT NULL AUTO_INCREMENT,
`name` VARCHAR(45) NOT NULL,
`addr_state` INT NOT NULL,
PRIMARY KEY (`id_customer`),
CONSTRAINT `fk_state1` <-- Here
FOREIGN KEY (`addr_state`)
REFERENCES `state` (`id_state`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;