我是StackOverflow的新手,所以如果我做错了,请抱歉。抱歉我的英语 - 这不是我的母语。
好的,长话短说。我正在使用:
Server version: 5.6.31 MySQL Community Server (GPL)
我有两张这样的表:
表格文字
CREATE TABLE `texts` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`body` text,
`source_id` int(11) unsigned DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `texts_sources_key` (`source_id`),
CONSTRAINT `texts_sources_key` FOREIGN KEY (`source_id`) REFERENCES `texts` (`id`) ON DELETE SET NULL ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8
table texts_sources
CREATE TABLE `texts_sources` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`short_desc` varchar(255) DEFAULT NULL,
`long_desc` text,
`url` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8
如您所见 - 有外键将这些表与 ON DELETE SET NULL ON UPDATE CASCADE 相关联。
这是初始数据:
mysql> select * from texts;
+----+------+-----------+
| id | body | source_id |
+----+------+-----------+
| 1 | *** | 1 |
+----+------+-----------+
1 row in set (0.00 sec)
mysql> select * from texts_sources;
+----+------------+-----------+----------------+
| id | short_desc | long_desc | url |
+----+------------+-----------+----------------+
| 1 | * | NULL | http://url.com |
+----+------------+-----------+----------------+
1 row in set (0.00 sec)
现在让我们做一些魔术。
mysql> update texts_sources set id=5;
Query OK, 1 row affected (0.05 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from texts_sources;
+----+------------+-----------+----------------+
| id | short_desc | long_desc | url |
+----+------------+-----------+----------------+
| 5 | * | NULL | http://url.com |
+----+------------+-----------+----------------+
1 row in set (0.01 sec)
mysql> select * from texts;
+----+------+-----------+
| id | body | source_id |
+----+------+-----------+
| 1 | *** | 1 |
+----+------+-----------+
1 row in set (0.00 sec)
不工作。更有趣:
mysql> delete from texts_sources;
Query OK, 1 row affected (0.18 sec)
mysql> select * from texts;
+----+------+-----------+
| id | body | source_id |
+----+------+-----------+
| 1 | *** | 1 |
+----+------+-----------+
1 row in set (0.00 sec)
不工作。好。也许它根本不起作用。让我们试试这个:
mysql> update texts set source_id=5;
ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`serj_by`.`texts`, CONSTRAINT `humor_sources_key` FOREIGN KEY (`source_id`) REFERENCES `texts` (`id`) ON DELETE SET NULL ON UPDATE CASCADE)
mysql> insert into texts (body, source_id) values ("***", 7);
ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`serj_by`.`texts`, CONSTRAINT `humor_sources_key` FOREIGN KEY (`source_id`) REFERENCES `texts` (`id`) ON DELETE SET NULL ON UPDATE CASCADE)
工作。乐趣。甚至更有趣(texts_sources是空的,希望你记得):
mysql> insert into texts (body, source_id) values ("***", 1);
Query OK, 1 row affected (0.16 sec)
mysql> select * from texts_sources;
Empty set (0.00 sec)
mysql> select * from texts;
+----+------+-----------+
| id | body | source_id |
+----+------+-----------+
| 1 | *** | 1 |
| 2 | *** | 1 |
+----+------+-----------+
2 rows in set (0.00 sec)
所以我的问题很明显。这是啥?如何使其在所有情况下都按预期工作?任何帮助都非常感谢。提前谢谢!
答案 0 :(得分:2)
让我们仔细看看:
CONSTRAINT `texts_sources_key`
FOREIGN KEY (`source_id`)
REFERENCES `texts` (`id`) ON DELETE SET NULL ON UPDATE CASCADE
虽然您将此命名为texts_sources_key
,但外键实际上引用了同一个表中的列。你可能想要它
CONSTRAINT `texts_sources_key`
FOREIGN KEY (`source_id`)
REFERENCES `texts_sources` (`id`) ON DELETE SET NULL ON UPDATE CASCADE
另外,在创建约束之前,您需要先创建text_sources表。