自己的MySQL外键(MySQL foreign keys on self)

 我目前正在尝试在MySQL中创建一个自引用表，但是似乎我无法在表本身上创建一个外键，我收到一个MySQL错误： 
 
Error Code: 1005. Can't create table 'biological classification' (errno: 150)
 
 这是我的代码： 
 
# Table creation
DROP TABLE IF EXISTS `biological classification`;
CREATE TABLE `biological classification` (
  `idBC` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `idParent` int(11) DEFAULT NULL,
  `type` varchar(45) DEFAULT NULL,
  `value` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`idBC`),
  UNIQUE KEY `idnew_table_UNIQUE` (`idBC`),
  CONSTRAINT `SelfKey` FOREIGN KEY (`idParent`) REFERENCES `biological classification` (`idBC`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=20 DEFAULT CHARSET=latin1 COMMENT='A table that contains the Biological Classification of anima';

# insert into table
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (1,NULL,'Class','Mammalia');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (2,1,'Genus','Giraffa');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (3,2,'Species','Giraffa camelopardalis');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (5,1,'Genus','Panthera');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (6,1,'Genus','Loxodonta');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (7,5,'Species','Panthera leo');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (8,5,'Species','Panthera tigris');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (9,6,'Species','Loxodonta africana');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (10,1,'Class','Marsupialia');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (11,10,'Genus','Macropus');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (12,11,'Species','Macropus rufus');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (13,1,'Genus','Sarcophilus');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (14,13,'Species','Sarcophilus harrisii');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (15,10,'Genus','Didelphis');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (16,15,'Species','Didelphis virginiana');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (17,NULL,'Class','Aves');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (18,17,'Genus','Aquila');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (19,18,'Species','Aquila chrysaetos');

I'm currently trying to make a self referencing table in MySQL, however it seems I can't make a foreign key on the table itself, I'm getting an MySQL error:
 
Error Code: 1005. Can't create table 'biological classification' (errno: 150)
 
This is my code:
 
# Table creation
DROP TABLE IF EXISTS `biological classification`;
CREATE TABLE `biological classification` (
  `idBC` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `idParent` int(11) DEFAULT NULL,
  `type` varchar(45) DEFAULT NULL,
  `value` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`idBC`),
  UNIQUE KEY `idnew_table_UNIQUE` (`idBC`),
  CONSTRAINT `SelfKey` FOREIGN KEY (`idParent`) REFERENCES `biological classification` (`idBC`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=20 DEFAULT CHARSET=latin1 COMMENT='A table that contains the Biological Classification of anima';

# insert into table
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (1,NULL,'Class','Mammalia');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (2,1,'Genus','Giraffa');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (3,2,'Species','Giraffa camelopardalis');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (5,1,'Genus','Panthera');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (6,1,'Genus','Loxodonta');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (7,5,'Species','Panthera leo');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (8,5,'Species','Panthera tigris');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (9,6,'Species','Loxodonta africana');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (10,1,'Class','Marsupialia');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (11,10,'Genus','Macropus');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (12,11,'Species','Macropus rufus');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (13,1,'Genus','Sarcophilus');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (14,13,'Species','Sarcophilus harrisii');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (15,10,'Genus','Didelphis');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (16,15,'Species','Didelphis virginiana');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (17,NULL,'Class','Aves');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (18,17,'Genus','Aquila');
INSERT INTO `biological classification` (`idBC`,`idParent`,`type`,`value`) VALUES (19,18,'Species','Aquila chrysaetos');

原文：https://stackoverflow.com/questions/7230145