想监控Bugzilla数据库中几个重要的表，如果它们发生了任何改变（增、删、改），都希望能够记录下来，以便后面再写程序来分析。很自然，就想到使用MySQL的触发器（Trigger）了，学习了一会，记录如下：
1. 先建立一个新的表用于记录我需要的变化：
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CREATE TABLE `bugzilla_log` ( `id` INT UNSIGNED NOT NULL, `table` varchar(80) NOT NULL, `action` ENUM('insert','update','delete'), `ts` TIMESTAMP ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='logging some important changes in bugzilla DB'; |
2. 针对需要监控的表，创建触发器：
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CREATE TRIGGER `classifications_insert` AFTER INSERT ON classifications FOR EACH ROW INSERT INTO `bugzilla_log` (`id`, `table`, `action`, `ts`) VALUES (NEW.id, 'classifications', 'insert', NOW()); CREATE TRIGGER `classifications_update` AFTER UPDATE ON classifications FOR EACH ROW INSERT INTO `bugzilla_log` (`id`, `table`, `action`, `ts`) VALUES (NEW.id, 'classifications', 'update', NOW()); CREATE TRIGGER `classifications_delete` BEFORE DELETE ON classifications FOR EACH ROW INSERT INTO `bugzilla_log` (`id`, `table`, `action`, `ts`) VALUES (OLD.id, 'classifications', 'delete', NOW()); |
请注意其中AFTER和BEFORE，以及OLD和NEW的使用。
Within the trigger body, you can refer to columns in the subject table (the table associated with the trigger) by using the aliases OLD and NEW. OLD.col_name refers to a column of an existing row before it is updated or deleted. NEW.col_name refers to the column of a new row to be inserted or an existing row after it is updated.
3. 查看当前数据库中的触发器：
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SHOW TRIGGERS; |
参考资料：
http://dev.mysql.com/doc/refman/5.5/en/create-trigger.html
http://www.jicdesign.com/blog/web-development/how-to-use-mysql-triggers-to-log-table-changes.html