Question

我想知道为什么我无法添加这个外键。这是我的架构

CREATE TABLE members(
  member_id INT NOT NULL AUTO_INCREMENT,
  name VARCHAR(50) NOT NULL,
  num_1 int,
  num_2 int,
  password VARCHAR(50) NOT NULL,
  PRIMARY KEY (member_id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE contacts(
  contact_id INT NOT NULL AUTO_INCREMENT,
  s1 int,
  phone_number VARCHAR(10) NOT NULL,
  s2 int,
  s3 int,
  PRIMARY KEY (contact_id),
  FOREIGN KEY (s1) REFERENCES members(num_1) ON DELETE CASCADE ON UPDATE CASCADE,
  FOREIGN KEY (s2) REFERENCES members(num_2) ON DELETE CASCADE ON UPDATE CASCADE,
  FOREIGN KEY (s3) REFERENCES members(member_id) ON DELETE CASCADE ON UPDATE CASCADE
)ENGINE=InnoDB DEFAULT CHARSET=utf8

我在mysql终端上收到此错误 ERROR 1215 (HY000): Cannot add foreign key constraint

我的架构有问题吗？。

Answer 1

这样对我有用：

CREATE TABLE members(
  member_id INT NOT NULL AUTO_INCREMENT,
  name VARCHAR(50) NOT NULL,
  num_1 int,
  num_2 int,
  password VARCHAR(50) NOT NULL,
  PRIMARY KEY (member_id),
  key idx_num1 (num_1),
  key idx_num2 (num_2)
)ENGINE=InnoDB DEFAULT CHARSET=utf8;


CREATE TABLE contacts(
  contact_id INT NOT NULL AUTO_INCREMENT,
  s1 int,
  phone_number VARCHAR(10) NOT NULL,
  s2 int,
  s3 int,
  PRIMARY KEY (contact_id),
  FOREIGN KEY (s1) REFERENCES members(num_1) ON DELETE CASCADE ON UPDATE CASCADE,
  FOREIGN KEY (s2) REFERENCES members(num_2) ON DELETE CASCADE ON UPDATE CASCADE,
  FOREIGN KEY (s3) REFERENCES members(member_id) ON DELETE CASCADE ON UPDATE CASCADE
)ENGINE=InnoDB DEFAULT CHARSET=utf8;

刚刚添加

  key idx_num1 (num_1),
  key idx_num2 (num_2)

表成员中的

。外键需要引用索引列（不一定是唯一的，不一定是NOT NULL能够的。）

来自manual：

InnoDB允许外键引用任何索引列或列组。但是，在引用的表中，必须有一个索引，其中引用的列被列为相同顺序的第一列。

无法添加多个外键

1 个答案: