mysql外鍵
https://stackoverflow.com/questions/1905470/cannot-delete-or-update-a-parent-row-a-foreign-key-constraint-fails
CREATE TABLE IF NOT EXISTS `advertisers` (
`advertiser_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
`password` char(32) NOT NULL,
`email` varchar(128) NOT NULL,
`address` varchar(255) NOT NULL,
`phone` varchar(255) NOT NULL,
`fax` varchar(255) NOT NULL,
`session_token` char(30) NOT NULL,
PRIMARY KEY (`advertiser_id`),
UNIQUE KEY `email` (`email`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=2 ;
INSERT INTO `advertisers` (`advertiser_id`, `name`, `password`, `email`, `address`, `phone`, `fax`, `session_token`) VALUES
(1, ‘TEST COMPANY‘, ‘‘, ‘‘, ‘‘, ‘‘, ‘‘, ‘‘);
CREATE TABLE IF NOT EXISTS `jobs` (
`job_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`advertiser_id` int(11) unsigned NOT NULL,
`name` varchar(255) NOT NULL,
`shortdesc` varchar(255) NOT NULL,
`longdesc` text NOT NULL,
`address` varchar(255) NOT NULL,
`time_added` int(11) NOT NULL,
`active` tinyint(1) NOT NULL,
`moderated` tinyint(1) NOT NULL,
PRIMARY KEY (`job_id`),
KEY `advertiser_id` (`advertiser_id`,`active`,`moderated`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=2 ;
INSERT INTO `jobs` (`job_id`, `advertiser_id`, `name`, `shortdesc`, `longdesc`, `address`, `active`, `moderated`) VALUES
(1, 1, ‘TEST‘, ‘TESTTEST‘, ‘TESTTESTES‘, ‘‘, 0, 0);
ALTER TABLE `advertisers`
ADD CONSTRAINT `advertisers_ibfk_1` FOREIGN KEY (`advertiser_id`) REFERENCES `jobs` (`advertiser_id`);
1.第一種情況
advertisers 設置外鍵
advertisers_ibfk_1 advertiser_id db03 jobs advertiser_id CASCADE RESTRICT
那麽
刪除的話，父和字表都可以刪除，如果RESTRICT，父表不能刪除
更新和插入的話，必須先插入字表，然後在插入父表，而且advertiser_id必須一致
比如
INSERT INTO `jobs` (`job_id`, `advertiser_id`, `name`, `shortdesc`, `longdesc`, `address`, `active`, `moderated`) VALUES
(1, 2, ‘TEST‘, ‘TESTTEST‘, ‘TESTTESTES‘, ‘‘, 0, 0);
INSERT INTO `advertisers` (`advertiser_id`, `name`, `password`, `email`, `address`, `phone`, `fax`, `session_token`) VALUES
(2, ‘TEST COMPANY‘, ‘‘, ‘‘, ‘‘, ‘‘, ‘‘, ‘‘);
2.第二種情況
如果兩個表都設置了外鍵
ALTER TABLE `jobs`
ADD FOREIGN KEY (`advertiser_id`) REFERENCES `advertisers` (`advertiser_id`);
advertiser
advertisers_ibfk_1 advertiser_id db03 jobs advertiser_id CASCADE RESTRICT
jobs
jobs_ibfk_1 advertiser_id db03 advertisers advertiser_id RESTRICT RESTRICT
delete from advertisers where advertiser_id=‘2‘; 無法刪除
INSERT INTO `advertisers` (`advertiser_id`, `name`, `password`, `email`, `address`, `phone`, `fax`, `session_token`) VALUES
(3, ‘TEST COMPANY‘, ‘‘, ‘‘, ‘‘, ‘‘, ‘‘, ‘‘);
INSERT INTO `jobs` (`job_id`, `advertiser_id`, `name`, `shortdesc`, `longdesc`, `address`, `active`, `moderated`) VALUES
(2, 3, ‘TEST‘, ‘TESTTEST‘, ‘TESTTESTES‘, ‘‘, 0, 0);
執行兩個insert全部報錯
[SQL]INSERT INTO `jobs` (`job_id`, `advertiser_id`, `name`, `shortdesc`, `longdesc`, `address`, `active`, `moderated`) VALUES
(2, 3, ‘TEST‘, ‘TESTTEST‘, ‘TESTTESTES‘, ‘‘, 0, 0);
[Err] 1452 - Cannot add or update a child row: a foreign key constraint fails (`db03`.`jobs`, CONSTRAINT `jobs_ibfk_1` FOREIGN KEY (`advertiser_id`) REFERENCES `advertisers` (`advertiser_id`))
外鍵總結
1.CASCADE RESTRICT的區別
2.如果是RESTRICT，insert必須先插入字表，就是沒有外鍵的表
3.如果是RESTRICT，delete必須先刪父表，然後再刪除子表
4.如果是整個drop 父表，還是會報錯的，只能先禁用外鍵
本文出自 “要有夢想，萬一實現了呢” 博客，請務必保留此出處http://szgb17.blog.51cto.com/340201/1971646
mysql外鍵