如何获取更新后生成的哈希值？
thufir@dur:~$
thufir@dur:~$ mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 138
Server version: 5.1.58-1ubuntu1 (Ubuntu)
Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
This software comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to modify and redistribute it under the GPL v2 license
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> use nntp;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
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 | |
| hash | char(32) | NO | | NULL | |
+-----------+----------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
mysql> show triggers;
+-----------+--------+------------+-----------------------------------------------------+--------+---------+----------+----------------+----------------------+----------------------+--------------------+
| Trigger | Event | Table | Statement | Timing | Created | sql_mode | Definer | character_set_client | collation_connection | Database Collation |
+-----------+--------+------------+-----------------------------------------------------+--------+---------+----------+----------------+----------------------+----------------------+--------------------+
| make_hash | INSERT | newsgroups | BEGIN
set new.hash = md5(new.newsgroup);
END | BEFORE | NULL | | root@localhost | utf8 | utf8_general_ci | latin1_swedish_ci |
+-----------+--------+------------+-----------------------------------------------------+--------+---------+----------+----------------+----------------------+----------------------+--------------------+
1 row in set (0.00 sec)
mysql>
mysql>
mysql> DELIMITER $$
mysql>
mysql> USE `nntp`$$
Database changed
mysql> CREATE
-> TRIGGER `nntp`.`make_hash_update`
-> AFTER UPDATE ON `nntp`.`newsgroups`
-> FOR EACH ROW
-> BEGIN
-> set old.hash = md5(new.newsgroup);
-> END$$
ERROR 1362 (HY000): Updating of OLD row is not allowed in trigger
mysql>
mysql> quit;
-> exit
-> ^CCtrl-C -- exit!
Aborted
thufir@dur:~$
此外，从工作台中，我看到旧的触发器:
但不知道如何添加额外的触发器。
最佳答案
不是更新后，而是更新前，而且是新的。不太明白语法，但这至少不会产生语法错误。想要使用工作台:
thufir@dur:~$
thufir@dur:~$ mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 144
Server version: 5.1.58-1ubuntu1 (Ubuntu)
Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
This software comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to modify and redistribute it under the GPL v2 license
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> use nntp;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
mysql> show triggers;
+-----------+--------+------------+-----------------------------------------------------+--------+---------+----------+----------------+----------------------+----------------------+--------------------+
| Trigger | Event | Table | Statement | Timing | Created | sql_mode | Definer | character_set_client | collation_connection | Database Collation |
+-----------+--------+------------+-----------------------------------------------------+--------+---------+----------+----------------+----------------------+----------------------+--------------------+
| make_hash | INSERT | newsgroups | BEGIN
set new.hash = md5(new.newsgroup);
END | BEFORE | NULL | | root@localhost | utf8 | utf8_general_ci | latin1_swedish_ci |
+-----------+--------+------------+-----------------------------------------------------+--------+---------+----------+----------------+----------------------+----------------------+--------------------+
1 row in set (0.00 sec)
mysql> show create trigger make_hash;
+-----------+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
| Trigger | sql_mode | SQL Original Statement | character_set_client | collation_connection | Database Collation |
+-----------+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
| make_hash | | CREATE DEFINER=`root`@`localhost` TRIGGER `nntp`.`make_hash`
BEFORE INSERT ON `nntp`.`newsgroups`
FOR EACH ROW
BEGIN
set new.hash = md5(new.newsgroup);
END | utf8 | utf8_general_ci | latin1_swedish_ci |
+-----------+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
1 row in set (0.00 sec)
mysql>
mysql> DELIMITER $$
mysql>
mysql> USE `nntp`$$
Database changed
mysql> CREATE
-> TRIGGER `nntp`.`make_hash_update`
-> BEFORE UPDATE ON `nntp`.`newsgroups`
-> FOR EACH ROW
-> BEGIN
-> set new.hash = md5(new.newsgroup);
-> END$$
Query OK, 0 rows affected (0.19 sec)
mysql>
mysql> show triggers;
-> ^CCtrl-C -- exit!
Aborted
thufir@dur:~$
关于mysql - before update 触发器生成哈希的语法，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/11707511/