将带有FOREIGN KEY的表添加到MySQL数据库会导致errno 150

Question

I'm attemping to execute the following SQL and am receiving errno: 150 'cannot create table path_relations' in response. According to the MySQL documentation this is caused by my FOREIGN KEY restraints having issues. What am I doing wrong?

DROP TABLE IF EXISTS `paths`;
DROP TABLE IF EXISTS `path_relations`;

CREATE TABLE `paths` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(256) CHARACTER SET utf8 DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=24 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

CREATE TABLE `path_relations` (
    `ancestor` int(11) NOT NULL DEFAULT '0',
    `descendant` int(11) NOT NULL DEFAULT '0',
    PRIMARY KEY(`ancestor`, `descendant`),
    FOREIGN KEY(`ancestor`) REFERENCES paths(`id`),
    FOREIGN KEY(`descendant`) REFERENCES paths(`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

Answer 1

Here is a checklist for you, good luck ;)

1) type of foreign key source and reference fields must be identical

2) both source and reference fields must be unsigned

3) source field must be indexed

4) both tables must be InnoDB

Answer 2

如果您将paths.id 未签名，是否paths.id ？

Answer 3

UPDATED: In the first table you define your integer value as unsigned whilst in the second you haven't. The fields must be identical in structure to satisfy a foreign key.

Do you have any data in the table already? if so make sure that all records would satisfy the constraint. NULL values in the foreign keyed column will prevent this from working.