mysql无法添加外键：错误1215（hy000）

Question

我收到错误 1215 (hy000)：无法添加外键约束，然后我运行以下 .sql 文件。下面的代码也没有创建文档表，可能是因为它无法创建外键。谁能告诉我如何修复下面的代码，以便它创建包含外键的文档表而不会引发错误：

CREATE DATABASE IF NOT EXISTS petclinic;
GRANT ALL PRIVILEGES ON petclinic.* TO pc@localhost IDENTIFIED BY 'pc';

USE petclinic;

CREATE TABLE IF NOT EXISTS types (
  id INT(4) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
  name VARCHAR(80),
  INDEX(name)
) engine=InnoDB;

CREATE TABLE IF NOT EXISTS documenttypes (
  id INT(4) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
  name VARCHAR(80),
  INDEX(name)
) engine=InnoDB;

CREATE TABLE IF NOT EXISTS owners (
  id INT(4) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
  first_name VARCHAR(30),
  last_name VARCHAR(30),
  address VARCHAR(255),
  city VARCHAR(80),
  telephone VARCHAR(20),
  INDEX(last_name)
) engine=InnoDB;

CREATE TABLE IF NOT EXISTS pets (
  id INT(4) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
  name VARCHAR(30),
  birth_date DATE,
  type_id INT(4) UNSIGNED NOT NULL,
  owner_id INT(4) UNSIGNED NOT NULL,
  INDEX(name),
  FOREIGN KEY (owner_id) REFERENCES owners(id),
  FOREIGN KEY (type_id) REFERENCES types(id)
) engine=InnoDB;

CREATE TABLE IF NOT EXISTS documents (
  id int(11) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
  client_id int(4) NOT NULL,
  type_id INT(4), 
  name varchar(200) NOT NULL,
  description text NOT NULL,
  filename varchar(200) NOT NULL,
  content mediumblob NOT NULL, 
  content_type varchar(255) NOT NULL,
  created timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  FOREIGN KEY (client_id) REFERENCES owners(id),
  FOREIGN KEY (type_id) REFERENCES documenttypes(id)
) engine=InnoDB;

我尝试了at this link 的建议，但这些建议都不适用于此代码。有人可以向我展示一些可以使用此代码的东西吗？

Answer 1

外键列的数据类型必须与原始列完全相同。

试试这个：

CREATE TABLE IF NOT EXISTS documents (
  id int(11) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
  client_id int(4) UNSIGNED NOT NULL,
  type_id INT(4) UNSIGNED NOT NULL, 
  name varchar(200) NOT NULL,
  description text NOT NULL,
  filename varchar(200) NOT NULL,
  content mediumblob NOT NULL, 
  content_type varchar(255) NOT NULL,
  created timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  FOREIGN KEY (client_id) REFERENCES owners(id),
  FOREIGN KEY (type_id) REFERENCES documenttypes(id)
) engine=InnoDB;

添加了UNSIGNED 到client_id 和UNSIGNED NOT NULL 到type_id（虽然NOT NULL 部分不是强制性的）

sqlfiddle demo