语法插入

Question

好之前触发，所以我see，这种错误的做法：

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> 

的已经应该用trigger填充？

好了，因为我的根做了一个触发像这样：

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。我怎么能让这个触发器实际上创建哈希？

Answer 1

我认为你应该保持原来的主键。
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); 

填充它，然后删除重复项，并添加你的唯一约束。

您还可以添加BEFORE INSERT和BEFORE UPDATE触发器设置hash值

CREATE DEFINER=`root`@`localhost` 
TRIGGER `before_insert_newsgroups` 
BEFORE INSERT ON `newsgroups` 
FOR EACH ROW BEGIN 

    set new.hash = md5(new.newsgroup); 

END 

根据不同的SQL客户端上使用的是你可能wan't到change the DELIMITER before and after the create trigger statement