错误1452(23000):无法添加或更新子行:外键约束失败

Question

当我执行以下SQL命令时:

INSERT INTO test_usershosts (RID,userid,hid,Usr,Pass) 
VALUES (NULL,1,1,"user","pass");

我收到以下错误消息:

ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint f
ails (`dm`.`test_usershosts`, CONSTRAINT `test_usershosts_ibfk_1` FOREIGN KEY (`
userid`) REFERENCES `test_users` (`userid`) ON DELETE CASCADE ON UPDATE CASCADE)

我的桌子:

CREATE TABLE IF NOT EXISTS `test_users` (
`userid` int(11) NOT NULL AUTO_INCREMENT,
`username` varchar(10) NOT NULL DEFAULT '',
`password` varchar(50) NOT NULL DEFAULT '',
PRIMARY KEY (userid)
) ENGINE=InnoDB;

INSERT INTO `test_users` (`userid`, `username`, `password) VALUES
(1120, 'guest', '12250170a9624f336ca24');

CREATE TABLE IF NOT EXISTS `test_hosts` (
`hid` int(11) NOT NULL AUTO_INCREMENT,
`UID` int(11) NOT NULL,
`name` varchar(100) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL,
PRIMARY KEY (hid)
) ENGINE=InnoDB;

INSERT INTO `test_hosts` (`hid`, `UID`, `name`) VALUES (30, 10, 'MU');

CREATE TABLE IF NOT EXISTS `test_usershosts` (
`RID` int(11) NULL AUTO_INCREMENT,
`userid` int(11) ,
`hid` int(11) ,
`Usr` varchar(100) ,
`Pass` varchar(100) ,
PRIMARY KEY (RID),
INDEX (userid),
INDEX (hid),
FOREIGN KEY (userid) REFERENCES test_users (userid) 
    ON DELETE CASCADE ON UPDATE CASCADE,
FOREIGN KEY (hid) REFERENCES test_hosts (hid) 
    ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB;

我调查了很多类似的案例,但找不到任何解决方案.任何帮助,将不胜感激.

Answer 1

您获得该异常的原因是因为您在表上插入了一个记录,test_usershosts该记录的值userID不存在于表中test_users.与hid表中不存在的值相同test_hosts.

表test_usershosts依赖于表:test_users和 test_hosts.因此,请确保在表上插入记录时test_usershosts,父表的值hid和userid已存在:test_users和 test_hosts.

尝试执行此查询,肯定会插入.

INSERT INTO test_usershosts (RID,userid,hid,Usr,Pass) 
VALUES (NULL,1120,30,'user','pass');

• SQLFiddle演示

我AUTO_INCREMENT在表上看到了这个选项:test_users并且 test_hosts,因为要在两个表上执行的每个查询上提供值,所以不需要.