mysql

Question

嗨，我知道有人问过这个问题，但我还没有找到正确的答案，当我尝试进行第二次插入时怎么会这样：

INSERT INTO phone_numbers (phone_number) VALUES ('226');

我收到错误：

ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (week7.phone_numbers, CONSTRAINT phone_numbers_ibfk_1 FOREIGN KEY (user_id) REFERENCES users (id))

下面的 DDL 代码：

create table users (
  id int unsigned not null auto_increment,
  name varchar(100) not null,
  primary key(id)
);

INSERT INTO users (name) VALUES ('alex');


create table phone_numbers (
  id int unsigned not null auto_increment,
  user_id int unsigned not null,
  phone_number varchar(25) not null,
  primary key(id),
  foreign key (user_id) references users (id)

);

 INSERT INTO phone_numbers (phone_number) VALUES ('226');

Answer 1

因为在您的 user_id 字段中没有默认值，这就是为什么它会抛出错误，如下所示，您的插入将起作用

INSERT INTO phone_numbers (user_id,phone_number) VALUES (1,'226');

mysql - 外键约束失败

mysql - Foreign Key Constraint Fails

sql

ddl