錯誤：無法添加或更新子行：外鍵約束失敗？

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)

在最後一天半的時間裏得到這條消息。試圖在兩個表之間建立一對多（外鍵）關係。在users:id和leavetable:users_id之間。當用戶登錄時，他們會得到一個ID。當他們將表格提交給hours列時，我希望ID能夠保留表格數據。當有人創建一個新的身份證號碼並且不會更新leavetable:user_id時，它會拋出錯誤。它會拋出上面的錯誤。

這裏是我的代碼：

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; 

我的表結構：

+---------------------+ 
| 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，你必須清理子表的數據，那麼mastertable之間清晰的外鍵後，你可以清除所有數據