Question

我尝试使用两个外键字段创建表格训练。但MySQL显示错误[1215]无法添加外键约束。我检查了父表是否已创建且两个字段的类型相同。还有什么可能是错的？

drop table if exists areas;
drop table if exists roles;
drop table if exists trainers;
drop table if exists users;
drop table if exists workouts;
drop table if exists user_roles;
drop table if exists trainers_areas;

CREATE TABLE areas(
  id INTEGER UNSIGNED PRIMARY KEY AUTO_INCREMENT NOT NULL,
  name VARCHAR(30)
);

CREATE TABLE roles(
  id INTEGER UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
  role VARCHAR(30)
);

create TABLE trainers(
  id INTEGER UNSIGNED PRIMARY KEY AUTO_INCREMENT NOT NULL,
  name VARCHAR(30) NOT NULL,
  birthday TIMESTAMP,
  sex CHAR(1)
);

create TABLE users(
  id INTEGER PRIMARY KEY AUTO_INCREMENT NOT NULL,
  name VARCHAR(30) NOT NULL,
  email VARCHAR(20),
  password VARCHAR(20),
  registered TIMESTAMP DEFAULT now(),
  enabled BOOL DEFAULT TRUE
);

CREATE TABLE workouts(
  id INTEGER UNSIGNED PRIMARY KEY  NOT NULL AUTO_INCREMENT,
  area_id INTEGER UNSIGNED NOT NULL,
  trainer_id INTEGER UNSIGNED NOT NULL,
  date TIMESTAMP,
  completed BOOLEAN NOT NULL,
 CONSTRAINT FOREIGN KEY (area_id) REFERENCES areas(id),
 CONSTRAINT FOREIGN KEY (trainer_id) REFERENCES trainers(id)
);


CREATE TABLE users_roles(
  user_id INTEGER UNSIGNED NOT NULL,
  role_id INTEGER UNSIGNED NOT NULL,
  FOREIGN KEY (user_id) REFERENCES users(id),
  FOREIGN KEY (role_id) REFERENCES roles(id)
);

CREATE TABLE trainers_areas(
  area_id INTEGER UNSIGNED NOT NULL,
  treiner_id INTEGER UNSIGNED NOT NULL,
  FOREIGN KEY (area_id) REFERENCES areas(id),
  FOREIGN KEY (treiner_id) REFERENCES trainers(id),
  UNIQUE (treiner_id, area_id)
);

Answer 1

数据类型必须匹配，SIGN也是如此。如果您未指定UNSIGNED，则会签名。

与另一个答案中提到的foreign_key_checks混淆，我会做最后一件事。人们经常忘记他们做到了，并猜测问题出现在哪里：Stackoverflow。

以下内容可行：

创建测试平台：

create schema Monday001a;
use Monday001a;

脚本：

drop table if exists areas;
drop table if exists roles;
drop table if exists trainers;
drop table if exists users;
drop table if exists workouts;
drop table if exists user_roles;
drop table if exists trainers_areas;

CREATE TABLE areas(
  id INTEGER UNSIGNED PRIMARY KEY AUTO_INCREMENT NOT NULL,
  name VARCHAR(30)
);

CREATE TABLE roles(
  id INTEGER UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
  role VARCHAR(30)
);

create TABLE trainers(
  id INTEGER UNSIGNED PRIMARY KEY AUTO_INCREMENT NOT NULL,
  name VARCHAR(30) NOT NULL,
  birthday TIMESTAMP,
  sex CHAR(1)
);

create TABLE users(
  id INTEGER UNSIGNED PRIMARY KEY AUTO_INCREMENT NOT NULL,
  name VARCHAR(30) NOT NULL,
  email VARCHAR(20),
  password VARCHAR(20),
  registered TIMESTAMP DEFAULT now(),
  enabled BOOL DEFAULT TRUE
);

CREATE TABLE workouts(
  id INTEGER UNSIGNED PRIMARY KEY  NOT NULL AUTO_INCREMENT,
  area_id INTEGER UNSIGNED NOT NULL,
  trainer_id INTEGER UNSIGNED NOT NULL,
  date TIMESTAMP,
  completed BOOLEAN NOT NULL,
 CONSTRAINT FOREIGN KEY (area_id) REFERENCES areas(id),
 CONSTRAINT FOREIGN KEY (trainer_id) REFERENCES trainers(id)
);


CREATE TABLE users_roles(
  user_id INTEGER UNSIGNED NOT NULL,
  role_id INTEGER UNSIGNED NOT NULL,
  FOREIGN KEY (user_id) REFERENCES users(id),
  FOREIGN KEY (role_id) REFERENCES roles(id)
);

CREATE TABLE trainers_areas(
  area_id INTEGER UNSIGNED NOT NULL,
  treiner_id INTEGER UNSIGNED NOT NULL,
  FOREIGN KEY (area_id) REFERENCES areas(id),
  FOREIGN KEY (treiner_id) REFERENCES trainers(id),
  UNIQUE (treiner_id, area_id)
);

清理：

drop schema Monday001a;

来自名为Using FOREIGN KEY Constraints的MySQL手册页：

外键和引用键中的对应列必须有类似的数据类型。整数类型的大小和符号必须是相同。字符串类型的长度不必相同。对于非二进制（字符）字符串列，字符集和排序规则必须是一样的。

Answer 2

要查找特定错误，请执行以下操作：

SHOW ENGINE INNODB STATUS

查看LATEST FOREIGN KEY ERROR部分。

子列的数据类型必须与父列完全匹配。例如，由于medicalhistory.MedicalHistoryID是INT，Patient.MedicalHistory也需要是INT，而不是SMALLINT。

此外，您应该在运行DDL之前运行查询set foreign_key_checks=0，以便您可以按任意顺序创建表，而不需要在相关子表之前创建所有父表。

Answer 3

在每个区块后添加ENGINE = INNODB。

1215无法添加外键约束

3 个答案: