循环外键约束失败mysql

清泉水

如果我在InnoDB数据库设计在发动机上，有三个表不能删除，因为每个表都说外键约束失败-这是否意味着设计错误？
7 |& F4 t8 V# _6 P0 a7 O请参阅以下结构：
CREATE TABLE IF NOT EXISTS `account` (  `account_id` smallint(5) unsigned NOT NULL AUTO_INCREMENT, PRIMARY KEY (`account_id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;CREATE TABLE IF NOT EXISTS `identity` (  `identity_id` int(10) unsigned NOT NULL AUTO_INCREMENT, `user_id` int(10) unsigned DEFAULT NULL, `account_id` smallint(5) unsigned DEFAULT NULL, PRIMARY KEY (`identity_id`), KEY `fk_details1` (`user_id`),    KEY `fk_account1` (`account_id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;CREATE TABLE IF NOT EXISTS `user` (  `user_id` int(10) unsigned NOT NULL AUTO_INCREMENT, `login` varchar(64) NOT NULL DEFAULT '', `password` varchar(32) NOT NULL DEFAULT '', `default_identity_id` int(10) unsigned DEFAULT NULL, PRIMARY KEY (`user_id`), UNIQUE KEY `login_UNIQUE` (`login`), KEY `fk_identity1` (`default_identity_id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;---- Constraints for table `identity`--ALTER TABLE `identity`  ADD CONSTRAINT `fk_details1` FOREIGN KEY (`user_id`) REFERENCES `user` (`user_id`) ON DELETE CASCADE ON UPDATE CASCADE, ADD CONSTRAINT `fk_account1` FOREIGN KEY (`account_id`) REFERENCES `account` (`account_id`) ON DELETE CASCADE ON UPDATE CASCADE;---- Constraints for table `user`--ALTER TABLE `user`  ADD CONSTRAINT `fk_identity1` FOREIGN KEY (`default_identity_id`) REFERENCES `identity` (`identity_id`) ON DELETE CASCADE ON UPDATE CASCADE;我怀疑问题出在default_identity_id …我应该把它作为标志移到身份表吗？
2 [. {0 G- g# |# e% s2 ?请指教！
                                                               
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