MySQL innodb - 外键：只有第一个有效？答案

【问题标题】：MySQL innodb - Foreign Key: only 1st works?MySQL innodb - 外键：只有第一个有效？
【发布时间】：2014-04-08 02:58:57
【问题描述】：

我在下面这个示例中无法创建customers_b。错误代码 1005 / 错误号：121。但是，如果我先创建customers_b 而不是customers_a，那么customers_a 将不会被创建。

怎么了？为什么我不能将多个 FK 链接到 PK 'id_state'？谢谢！

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;

【问题讨论】：

@DaImTo 该错误发生在创建表时，在进行任何插入之前。

标签： mysql create-table

【解决方案1】：

您的两个表约束名称相同 CONSTRAINT fk_state。为 customer_b 更改该名称，如下所示

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;

【讨论】：

【解决方案2】：

您不能对两个约束使用相同的名称fk_state。给其中一个取一个不同的名字。

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;

【讨论】：