MySQL 一直提示外键。错误 150

Question

我正在尝试创建一个自身带有外键的表。我想建模一个可以是另一个类别的子类别的类别。这是我的 SQL:

CREATE TABLE IF NOT EXISTS `recipes`.`category` (
  `id` INT NOT NULL COMMENT '',
  `name` VARCHAR(60) NOT NULL COMMENT '',
  `description` VARCHAR(255) NULL COMMENT 'Description of the recipe category.',
  `parent_id` INT NULL COMMENT '',
  PRIMARY KEY (`id`)  COMMENT '',
  CONSTRAINT `parent_id`
    FOREIGN KEY (`id`)
    REFERENCES `recipes`.`category` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION);

但是，MySQL 一直报错:

Can't create table 'recipes.category' (errno: 150)

我想找出我做错了什么，有人可以给我提示吗？文档说:

Cannot create table. If the error message refers to error 150, table creation failed because a foreign key constraint was not correctly formed.

但是，这对我帮助不大。

Answer 1

我想您希望 parent_id 列链接到 id 列(而不是 id 列 id column) 构建层次结构。否则它没有多大意义:

constraint `parent_id`
foreign key (`parent_id`)
references `category` (`id`)
on delete no action
on update no action);

SQLFiddle