外键存在时为什么'外键约束失败'？

我有一个简单的查询外键存在时为什么'外键约束失败'？

UPDATE `t_timecard_detail` SET `timeoff_request_id` = 'adad8e0d-c22b-41c3-a460-6cf982729299' WHERE `id` = 'cfc7a0a1-4e03-46a4-af89-069a0661cf55';

这给这个错误

ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`demo1_timeapp`.`t_timecard_detail`, CONSTRAINT `timeoff_request_id_refs_id_48fe5c4` FOREIGN KEY (`timeoff_request_id`) REFERENCES `t_timeoff_request` (`id`))

约束

CONSTRAINT `timeoff_request_id_refs_id_48fe5c4` FOREIGN KEY (`timeoff_request_id`) REFERENCES `t_timeoff_request` (`id`)

虽然ID 'adad8e0d-C22B-41c3-a460-6cf982729299' 的存在t_timeoff_request表

mysql> select `id` from t_timeoff_request where `id`='adad8e0d-c22b-41c3-a460-6cf982729299'; 
+--------------------------------------+ 
| id         | 
+--------------------------------------+ 
| adad8e0d-c22b-41c3-a460-6cf982729299 | 
+--------------------------------------+

所以我不确定当外键存在时为什么mysql会说'外键约束失败'？

MySQL版本：

$ mysql --version 
mysql Ver 14.14 Distrib 5.1.41, for debian-linux-gnu (i486) using readline 6.1

编辑：看起来像一个表具有ENGINE = MyISAM和其他innodb的

输出的show create table t_timecard_detail;

CREATE TABLE `t_timecard_detail` (
    `id` varchar(36) NOT NULL, 
    `change_time` datetime NOT NULL, 
    `department_id` varchar(36) DEFAULT NULL, 
    `day` date NOT NULL, 
    `in_punch_id` varchar(36) DEFAULT NULL, 
    `punch_in` datetime DEFAULT NULL, 
    `paid_in` datetime DEFAULT NULL, 
    `infraction_in_id` varchar(36) DEFAULT NULL, 
    `schedule_in` datetime DEFAULT NULL, 
    `type_in` varchar(10) NOT NULL, 
    `out_punch_id` varchar(36) DEFAULT NULL, 
    `punch_out` datetime DEFAULT NULL, 
    `paid_out` datetime DEFAULT NULL, 
    `schedule_out` datetime DEFAULT NULL, 
    `infraction_out_id` varchar(36) DEFAULT NULL, 
    `type_out` varchar(10) NOT NULL, 
    `work_min` int(11) NOT NULL, 
    `ot_min` int(11) NOT NULL, 
    `ot2_min` int(11) NOT NULL, 
    `pay_type_id` varchar(36) NOT NULL, 
    `timecard_id` varchar(36) NOT NULL, 
    `user_entered` tinyint(1) NOT NULL, 
    `comments` varchar(256) DEFAULT NULL, 
    `timeoff_request_id` varchar(36), 
    PRIMARY KEY (`id`), 
    KEY `t_timecard_detail_department_id` (`department_id`), 
    KEY `t_timecard_detail_in_punch_id` (`in_punch_id`), 
    KEY `t_timecard_detail_infraction_in_id` (`infraction_in_id`), 
    KEY `t_timecard_detail_out_punch_id` (`out_punch_id`), 
    KEY `t_timecard_detail_infraction_out_id` (`infraction_out_id`), 
    KEY `t_timecard_detail_pay_type_id` (`pay_type_id`), 
    KEY `t_timecard_detail_timecard_id` (`timecard_id`), 
    KEY `t_timecard_detail_4f5ffbb5` (`timeoff_request_id`), 
    CONSTRAINT `department_id_refs_id_1b23ee35` FOREIGN KEY (`department_id`) REFERENCES `t_department` (`id`), 
    CONSTRAINT `infraction_in_id_refs_id_17b2e173` FOREIGN KEY (`infraction_in_id`) REFERENCES `t_pay_group_infraction` (`id`), 
    CONSTRAINT `infraction_out_id_refs_id_17b2e173` FOREIGN KEY (`infraction_out_id`) REFERENCES `t_pay_group_infraction` (`id`), 
    CONSTRAINT `in_punch_id_refs_id_4d13a8b2` FOREIGN KEY (`in_punch_id`) REFERENCES `t_punch` (`id`), 
    CONSTRAINT `out_punch_id_refs_id_4d13a8b2` FOREIGN KEY (`out_punch_id`) REFERENCES `t_punch` (`id`), 
    CONSTRAINT `pay_type_id_refs_id_70cb7404` FOREIGN KEY (`pay_type_id`) REFERENCES `t_pay_type` (`id`), 
    CONSTRAINT `timecard_id_refs_id_7889236c` FOREIGN KEY (`timecard_id`) REFERENCES `t_timecard` (`id`), 
    CONSTRAINT `timeoff_request_id_refs_id_48fe5c4` FOREIGN KEY (`timeoff_request_id`) REFERENCES `t_timeoff_request` (`id`) 
) ENGINE=InnoDB DEFAULT CHARSET=latin1

输出的show create table t_timeoff_request;

CREATE TABLE `t_timeoff_request` (
    `id` varchar(36) NOT NULL, 
    `change_time` datetime NOT NULL, 
    `employee_id` varchar(36) NOT NULL, 
    `submitted_date` datetime NOT NULL, 
    `time_off_day` date NOT NULL, 
    `mins_charged` int(11) NOT NULL, 
    `pay_type_id` varchar(36) NOT NULL, 
    `employee_comment` varchar(300) NOT NULL, 
    `approved_status` varchar(10) NOT NULL, 
    `approved_by_id` varchar(36) DEFAULT NULL, 
    `approved_date` datetime DEFAULT NULL, 
    `approved_comment` varchar(300) DEFAULT NULL, 
    PRIMARY KEY (`id`), 
    KEY `t_timeoff_request_employee_id` (`employee_id`), 
    KEY `t_timeoff_request_pay_type_id` (`pay_type_id`), 
    KEY `t_timeoff_request_approved_by_id` (`approved_by_id`) 
) ENGINE=MyISAM DEFAULT CHARSET=latin1

来源

2010-10-08 Anurag Uniyal

show create table t_timecard_detail;显示创建表t_timeoff_request; – iddqd 2010-10-08 12:05:38

@iddqd，我粘贴了'create table'结构 – 2010-10-08 12:45:35

我认为这是一个错误。 MySQL不应允许您将InnoDB的FORISIGN KEY引用添加到MyISAM表中，因为MyISAM引擎不是事务性的，InnoDb是。

Try: 
ALTER TABLE t_timeoff_request ENGINE=InnoDB;

来源

2010-10-08 13:18:49 iddqd

是看起来像一个bug，它不应该允许一个外键，并可能导致非常微妙的错误 – 2010-10-08 14:10:52

我希望我可以upvote这个答案100次。我一直在解决这个问题好几个小时，果然，我的主表是MyISAM出于某种原因。谢谢你iddqd！ – Matt 2011-02-11 22:32:09

同样的错误！很荣幸iddqd！ – 2014-06-04 17:21:03

如果您在FK上设置了一个约束，那么问题可能出现在另一个表中。您是否设置了FK选项，如ON UPDATE CASCADE？

来源

2010-10-08 12:04:54 vulkanino

外键约束不能适用于MyISAM数据表engine.both应该使用InnoDB引擎支持外键约束。

来源

2012-02-04 07:19:30 Prakash

外键存在时为什么'外键约束失败'？

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