Question

ALTER TABLE book
ADD FOREIGN KEY (category_id)
REFERENCES category (category_id)
ON DELETE CASCADE
ON UPDATE CASCADE;

每当我运行这个ALTER TABLE语句时，它都会继续回复，＆＃34;错误代码：1072。键列＆＃39; category_id＆＃39;不存在。＆＃34;

我确定这是一个简单的解决方法，但我在向其中一个表添加外键时遇到问题。我上周刚开始学习SQL，所以任何帮助都将不胜感激！

我的CREATE TABLE语句如下：

CREATE TABLE IF NOT EXISTS book
(book_id INT not null PRIMARY KEY AUTO_INCREMENT,
title VARCHAR(100) not null,
description TEXT not null,
price DEC(18,2) not null
) ENGINE=InnoDB;

CREATE TABLE IF NOT EXISTS category
(category_id INT not null PRIMARY KEY AUTO_INCREMENT,
code1 VARCHAR(20) not null,
name1 VARCHAR(100) not null
) ENGINE=InnoDB;

Answer 1

CREATE TABLE IF NOT EXISTS category
(category_id INT not null PRIMARY KEY AUTO_INCREMENT,
code1 VARCHAR(20) not null,
name1 VARCHAR(100) not null
) ENGINE=InnoDB;

此表具有Primay Key category_id，但下表没有Column as＆＃34; category_id＆＃34;这是在Alter Command.Add中引用的列＆＃34; category_id在下表中，然后执行Alter命令。

CREATE TABLE IF NOT EXISTS book
(book_id INT not null PRIMARY KEY AUTO_INCREMENT,
title VARCHAR(100) not null,
description TEXT not null,
price DEC(18,2) not null
) ENGINE=InnoDB;

Answer 2

这是完整的脚本

CREATE TABLE IF NOT EXISTS book
(book_id INT not null PRIMARY KEY AUTO_INCREMENT,
title VARCHAR(100) not null,
description TEXT not null,
price DEC(18,2) not null,
category_id INT not null 
) ENGINE=InnoDB;

CREATE TABLE IF NOT EXISTS category
(category_id INT not null PRIMARY KEY AUTO_INCREMENT,
code1 VARCHAR(20) not null,
name1 VARCHAR(100) not null
) ENGINE=InnoDB;

ALTER TABLE book
ADD FOREIGN KEY (category_id)
REFERENCES category (category_id)
ON DELETE CASCADE
ON UPDATE CASCADE;

ALTER TABLE时不存在SQL键列

2 个答案: