Home/ Questions/Q 644117
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-13T21:21:23+00:00

mysql> ALTER TABLE category ADD CONSTRAINT category_parent_category_id FOREIGN KEY (parent) REFERENCES category(id); ERROR 1005

  • 0
mysql> ALTER TABLE category ADD CONSTRAINT category_parent_category_id FOREIGN KEY (parent) REFERENCES category(id);
ERROR 1005 (HY000): Can't create table 'sfnews.#sql-244_1' (errno: 150)

DDL as follows:

Create Table: CREATE TABLE `category` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) NOT NULL,
  `parent` bigint(20) unsigned DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `name` (`name`),
  KEY `parent_idx` (`parent`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1

Why is it wrong?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Self reference should be possible. It’s because “parent” is unsigned and “id” is not. Change the table definitions id column to

     `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,

    and it will work.

    The reference states about foreign keys: “The size and sign of integer types must be the same”

    Seems to be the same problem described here

    • 0