即使设置foreign_key_checks=0，也无法创建表（错误1215）；

Question

我尝试做的事情已经做了无数次，但现在从MySQL5.6.26升级到5.6.27失败了（在5.7.x中也失败了）。我有一个数据库，其中包含一堆带有外键约束的表。我导出了（使用phpMyAdmin）替换表，指定了以下导出选项：

Disable foreign key checks
Add DROP TABLE / VIEW / PROCEDURE / FUNCTION / EVENT / TRIGGER statement
Add CREATE TABLE statement

结果导出文件包含以下部分：

SET FOREIGN_KEY_CHECKS=0;

DROP TABLE IF EXISTS `application`;
CREATE TABLE `application` (
  `PK_Application` int(11) NOT NULL,
  `FK_Parent` int(11) DEFAULT NULL,
  `ApplicationLevel` tinyint(4) NOT NULL,
  `Description` varchar(35) NOT NULL,
  `Sequence` tinyint(4) NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=15 DEFAULT CHARSET=latin1;

. . .
. . .

DROP TABLE IF EXISTS `product_x_application`;
CREATE TABLE `product_x_application` (
  `PK_Product_X_Application` int(11) NOT NULL,
  `Product_PKID` varchar(36) NOT NULL,
  `FK_Application` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

. . .
. . .

ALTER TABLE `product_x_application`
  ADD CONSTRAINT `product_x_application_ibfk_2` FOREIGN KEY (`FK_Application`) REFERENCES `application` (`PK_Application`) ON DELETE CASCADE ON UPDATE CASCADE;

-- phpMyAdmin SQL Dump
-- version 4.4.15
-- http://www.phpmyadmin.net
--
-- Host: localhost
-- Generation Time: Jan 10, 2016 at 07:01 AM
-- Server version: 5.6.26-log
-- PHP Version: 5.6.12

SET FOREIGN_KEY_CHECKS=0;
SET SQL_MODE = "NO_AUTO_VALUE_ON_ZERO";
SET time_zone = "+00:00";


/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8mb4 */;

--
-- Database: `spmorell_sami`
--

-- --------------------------------------------------------

--
-- Table structure for table `application`
--

DROP TABLE IF EXISTS `application`;
CREATE TABLE `application` (
  `PK_Application` int(11) NOT NULL,
  `FK_Parent` int(11) DEFAULT NULL,
  `ApplicationLevel` tinyint(4) NOT NULL,
  `Description` varchar(35) NOT NULL,
  `Sequence` tinyint(4) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

-- --------------------------------------------------------

--
-- Table structure for table `product_x_application`
--

DROP TABLE IF EXISTS `product_x_application`;
CREATE TABLE `product_x_application` (
  `PK_Product_X_Application` int(11) NOT NULL,
  `Product_PKID` varchar(36) NOT NULL,
  `FK_Application` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

--
-- Indexes for dumped tables
--

--
-- Indexes for table `application`
--
ALTER TABLE `application`
  ADD PRIMARY KEY (`PK_Application`);

--
-- Indexes for table `product_x_application`
--
ALTER TABLE `product_x_application`
  ADD PRIMARY KEY (`PK_Product_X_Application`),
  ADD KEY `Product_PKID` (`Product_PKID`),
  ADD KEY `FK_Application` (`FK_Application`);

--
-- AUTO_INCREMENT for dumped tables
--

--
-- AUTO_INCREMENT for table `application`
--
ALTER TABLE `application`
  MODIFY `PK_Application` int(11) NOT NULL AUTO_INCREMENT;
--
-- AUTO_INCREMENT for table `product_x_application`
--
ALTER TABLE `product_x_application`
  MODIFY `PK_Product_X_Application` int(11) NOT NULL AUTO_INCREMENT;
--
-- Constraints for dumped tables
--

--
-- Constraints for table `product_x_application`
--
ALTER TABLE `product_x_application`
  ADD CONSTRAINT `product_x_application_ibfk_1` FOREIGN KEY (`Product_PKID`) REFERENCES `product` (`Product_PKID`) ON DELETE CASCADE ON UPDATE CASCADE,
  ADD CONSTRAINT `product_x_application_ibfk_2` FOREIGN KEY (`FK_Application`) REFERENCES `application` (`PK_Application`) ON DELETE CASCADE ON UPDATE CASCADE;
SET FOREIGN_KEY_CHECKS=1;

/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;

请注意，application表的主键是在ALTER table语句中定义的。以下是5.5服务器导出的文件：

-- phpMyAdmin SQL Dump
-- version 3.5.8.2
-- http://www.phpmyadmin.net
--
-- Host: localhost
-- Generation Time: Jan 10, 2016 at 05:09 AM
-- Server version: 5.5.42-37.1-log
-- PHP Version: 5.4.23

SET FOREIGN_KEY_CHECKS=0;
SET SQL_MODE="NO_AUTO_VALUE_ON_ZERO";
SET time_zone = "+00:00";

--
-- Database: `spmorell_sami`
--

-- --------------------------------------------------------

--
-- Table structure for table `application`
--

DROP TABLE IF EXISTS `application`;
CREATE TABLE `application` (
  `PK_Application` int(11) NOT NULL AUTO_INCREMENT,
  `FK_Parent` int(11) DEFAULT NULL,
  `ApplicationLevel` tinyint(4) NOT NULL,
  `Description` varchar(35) NOT NULL,
  `Sequence` tinyint(4) NOT NULL,
  PRIMARY KEY (`PK_Application`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=15 ;

-- --------------------------------------------------------

--
-- Table structure for table `product_x_application`
--

DROP TABLE IF EXISTS `product_x_application`;
CREATE TABLE `product_x_application` (
  `PK_Product_X_Application` int(11) NOT NULL AUTO_INCREMENT,
  `Product_PKID` varchar(36) NOT NULL,
  `FK_Application` int(11) NOT NULL,
  PRIMARY KEY (`PK_Product_X_Application`),
  KEY `Product_PKID` (`Product_PKID`),
  KEY `FK_Application` (`FK_Application`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=1633 ;

--
-- Constraints for dumped tables
--

--
-- Constraints for table `product_x_application`
--
ALTER TABLE `product_x_application`
  ADD CONSTRAINT `product_x_application_ibfk_2` FOREIGN KEY (`FK_Application`) REFERENCES `application` (`PK_Application`) ON DELETE CASCADE ON UPDATE CASCADE,
  ADD CONSTRAINT `product_x_application_ibfk_1` FOREIGN KEY (`Product_PKID`) REFERENCES `product` (`Product_PKID`) ON DELETE CASCADE ON UPDATE CASCADE;
SET FOREIGN_KEY_CHECKS=1;

这里，application表的主键在定义表时立即定义。我认为问题在于，product_x_application表（在系统试图重新创建application表时已经存在）对一个表有外键约束，该表在重新创建时没有外键上所需的索引，因为主键尚未定义。

Answer 1

外键应该引用唯一的列（例如，主键）。pk_application目前不是这样的列。但是，从它的名称来看，您似乎想让它成为一个主键：

ALTER TABLE `application` 
ADD CONSTRAINT `application_pk` PRIMARY KEY (`PK_Application`);