Mysql 插入前触发器的语法
好的,我认为这是错误的方法:Mysql 插入前触发器的语法,mysql,triggers,schema,constraints,mysql-error-1170,Mysql,Triggers,Schema,Constraints,Mysql Error 1170,好的,我认为这是错误的方法: mysql> mysql> show tables; +---------------------+ | Tables_in_nntp | +---------------------+ | articles | | newsgroups | | newsgroups_articles | +---------------------+ 3 rows in set (0.00 sec) mysql&g
mysql>
mysql> show tables;
+---------------------+
| Tables_in_nntp |
+---------------------+
| articles |
| newsgroups |
| newsgroups_articles |
+---------------------+
3 rows in set (0.00 sec)
mysql> describe newsgroups;
+-----------+----------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+----------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| newsgroup | longtext | NO | | NULL | |
+-----------+----------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
mysql> show create table newsgroups;
+------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| newsgroups | CREATE TABLE `newsgroups` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`newsgroup` longtext NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=7 DEFAULT CHARSET=latin1 |
+------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> ALTER TABLE newsgroups ADD UNIQUE (newsgroup);
ERROR 1170 (42000): BLOB/TEXT column 'newsgroup' used in key specification without a key length
mysql>
has应填充一个
好的,作为root,我做了一个触发器,如下所示:
mysql>
mysql> show tables;
+---------------------+
| Tables_in_nntp |
+---------------------+
| articles |
| newsgroups |
| newsgroups_articles |
+---------------------+
3 rows in set (0.00 sec)
mysql>
mysql> delimiter |
mysql> CREATE TRIGGER make_hash BEFORE INSERT ON newsgroups
-> FOR EACH ROW BEGIN
-> INSERT INTO hash values ('0');
-> END;
-> |
Query OK, 0 rows affected (0.18 sec)
mysql>
然而,这只是虚拟数据。我怎样才能使触发器真正创建散列呢?我认为您应该保持主键不变。
您可以添加一个哈希列
ALTER TABLE `newsgroups` ADD COLUMN `hash` CHAR(32) NOT NULL DEFAULT '';
然后用
UPDATE newsgroups SET hash = MD5(newsgroup);
然后删除重复项并添加唯一约束
您还可以在插入之前添加和更新之前添加触发器,以设置哈希值
CREATE DEFINER=`root`@`localhost`
TRIGGER `before_insert_newsgroups`
BEFORE INSERT ON `newsgroups`
FOR EACH ROW BEGIN
set new.hash = md5(new.newsgroup);
END
取决于您使用的SQL客户端,您可能不想我正在查看,您是否正在使用SQL来更改表?这些命令来自MySql控制台?它不是一个完整的语句,我添加了缺少的部分。ok创建了一个伪触发器,但无法获得您上面描述的那种触发器的语法。我似乎缺少一些东西。您需要另一个用于哈希的表?同一个表应该有新闻组(只有一个字符串,大约80个字符)和哈希,这样哈希就可以设置为唯一的。“TRIGGER command denied to user…”-您应该检查您的用户有哪些特权,并在必要时与其他用户一起运行“创建触发器”。@Vatev我将以root用户身份尝试,但我不认为这是问题所在,用户java有用法
。