Question

我在将数据插入表格时遇到问题。我已经多次重新创建了这两个表，试图解决我的问题。第一个表login，包含id（主键），用户名和密码。第二个表userinfo包含id（主键），名字，姓氏，电子邮件和登录$ id（引用登录主键ID的外键）。我可以很好地插入登录表，我总是首先插入，以便第二个表可以获得第一个表的id用作外键。但是一旦我将数据插入userinfo表，我就得到了 错误1452：无法添加或更新子行：外键constaint失败。 我不知道为什么它一直无法插入。任何帮助都会很好，谢谢你。

+-------+------------------+------+-----+---------+----------------+
| Field | Type             | Null | Key | Default | Extra          |
+-------+------------------+------+-----+---------+----------------+
| id    | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| user  | varchar(50)      | NO   |     | NULL    |                |
| passwd| varchar(50)      | NO   |     | NULL    |                |
+-------+------------------+------+-----+---------+----------------+

+-------------------+------------------+------+-----+---------+----------------+
| Field             | Type             | Null | Key | Default | Extra          |
+-------------------+------------------+------+-----+---------+----------------+
| id                | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| firstN            | varchar(50)      | NO   |     | NULL    |                |
| lastN             | varchar(50)      | NO   |     | NULL    |                |
| email             | varchar(125)     | NO   |     | NULL    |                |
| login$id          | int(10) unsigned | NO   | MUL | NULL    |                |
+-------------------+------------------+------+-----+---------+----------------+

这是我的表格代码

CREATE TABLE login(
  id INT UNSIGNED NOT NULL AUTO_INCREMENT,
  user VARCHAR(50) NOT NULL,
  passwd VARCHAR(50) NOT NULL,
  PRIMARY KEY (id)
);

CREATE TABLE userinfo(
  id INT UNSIGNED NOT NULL AUTO_INCREMENT,
  firstN VARCHAR(50) NOT NULL,
  lastN VARCHAR(50) NOT NULL,
  email VARCHAR(125) NOT NULL,
  login$id INT UNSIGNED NOT NULL,
  PRIMARY KEY (id),
  FOREIGN KEY (login$id) REFERENCES login(id)
);

Answer 1

This is because INSERT query for userinfo table does not have login id. You can get the last inserted id for login by using LAST_INSERT_ID() MySQL function and amend the queries like below:

INSERT INTO login (user, passwd) VALUES ('DDan', 'Password1');
INSERT INTO userinfo (firstN, lastN, email, login$id) VALUES ('Dan', 'Dan', 'email@yahoo.com', LAST_INSERT_ID());

Here's the SQL Fiddle, and here's the documentation for LAST_INSERT_ID().

MySQL无法添加行：外键约束失败

1 个答案: