错误：无法添加或更新子行：外键约束失败？

Question

Error: Cannot add or update a child row: a foreign key constraint fails? ( testlogin . leavetable , CONSTRAINT leavetable_ibfk_1 FOREIGN KEY
( users_id ) REFERENCES users ( id ) ON DELETE CASCADE ON UPDATE CASCADE)

Been getting this message for the last day and a half. Trying to make a one to many (foreign key) relationship between the two tables. Between users:id and leavetable:users_id . When user logs in they get a id. when they submit a form to column hours I'd like for the id to stay with the form data. It is throwing the error when someone creates a new id number and it wont update the leavetable:user_id . It throws the error above.

Here's my code:

CREATE TABLE IF NOT EXISTS `users` ( 
`email` varchar(255) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL, 
`id` int(11) NOT NULL, 
`password` char(64) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL, 
`salt` char(16) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL, 
`username` varchar(255) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL 
) ENGINE=InnoDB DEFAULT CHARSET=latin1; 



CREATE TABLE IF NOT EXISTS `leavetable` ( 
`hours` int(11) NOT NULL, 
`users_id` int(11) DEFAULT NOT NULL, 
`id` int(11) NOT NULL 
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1; 


 ALTER TABLE `users` 
 ADD PRIMARY KEY (`id`) USING BTREE, 
 ADD UNIQUE KEY `email` (`email`) USING BTREE, 
 ADD UNIQUE KEY `username` (`username`) USING BTREE; 

 ALTER TABLE `leavetable` 
 ADD PRIMARY KEY (`id`) USING BTREE, 
 ADD KEY `users_id` (`users_id`) USING BTREE; 

 ALTER TABLE `leavetable` 
 MODIFY `id` int(11) NOT NULL AUTO_INCREMENT; 
 -- AUTO_INCREMENT for table `users` 
 ALTER TABLE `users` 
 MODIFY `id` int(11) NOT NULL AUTO_INCREMENT; 

ALTER TABLE `leavetable` 
ADD CONSTRAINT `leavetable_ibfk_1` FOREIGN KEY (`users_id`) REFERENCES
`users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE;

my table structure:

+---------------------+
| Tables_in_testlogin |
+---------------------+
| leavetable          |
| users               |
+---------------------+

+----------+--------------+------+-----+---------+----------------+
| Field    | Type         | Null | Key | Default | Extra          |
+----------+--------------+------+-----+---------+----------------+
| email    | varchar(255) | NO   | UNI | NULL    |                |
| id       | int(11)      | NO   | PRI | NULL    | auto_increment |
| password | char(64)     | NO   |     | NULL    |                |
| salt     | char(16)     | NO   |     | NULL    |                |
| username | varchar(255) | NO   | UNI | NULL    |                |
+----------+--------------+------+-----+---------+----------------+
5 rows in set (0.01 sec)

+----------+---------+------+-----+---------+----------------+
| Field    | Type    | Null | Key | Default | Extra          |
+----------+---------+------+-----+---------+----------------+
| hours    | int(11) | NO   |     | NULL    |                |
| users_id | int(11) | NO   | MUL | NULL    |                |
| id       | int(11) | NO   | PRI | NULL    | auto_increment |
+----------+---------+------+-----+---------+----------------+
3 rows in set (0.01 sec)

Answer 1

首先，您必须清除子表的数据，然后清除mastertable之间的外键，之后您才能清除任何数据