圆形外键约束失败mysql

Question

如果我在InnoDB引擎上设计数据库，并且我有3个表，我无法删除，因为每个表示“外键约束失败” - 是否意味着设计错误？

请参阅下面的结构：

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; 

我怀疑问题是default_identity_id ...我将它作为一个标志，标识表？

请指教！

Answer 1

由于ypercube没有创建答案，我会的。

MySQL Database design. Inserting rows in 1to1 tables

这回答我的问题 - 它不仅仅是指向表彼此更好的和灵活的设计。谢谢。