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MySQL计划任务(事件调度器)(Event Scheduler)
 
 
修改时间:[2012/08/21 19:26]    阅读次数:[706]    发表者:[沩筱]
 

MySQL5.1.x版本中引入了一项新特性EVENT,顾名思义就是事件、定时任务机制,在指定的时间单元内执行特定的任务,因此今后一些对数据定时性操作不再依赖外部程序,而直接使用数据库本身提供的功能。要查看当前是否已开启事件调度器,可执行如下SQL:SHOW VARIABLES LIKE 'event_scheduler';
或SELECT @@event_scheduler;
或SHOW PROCESSLIST;
若显示:

+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| event_scheduler | OFF   |
+-----------------+-------+
则可执行SET GLOBAL event_scheduler = 1;
或SET GLOBAL event_scheduler = ON;
来开启,也可以直接在启动命令加上“–event_scheduler=1”,例如:mysqld ... --event_scheduler=1my.ini or my.cnf 中的
[mysqld]
添加 event_scheduler=ON创建事件(CREATE EVENT)
先来看一下它的语法:CREATE EVENT [IF NOT EXISTS] event_name
ON SCHEDULE schedule
[ON COMPLETION [NOT] PRESERVE]
[ENABLE | DISABLE]
[COMMENT 'comment']
DO sql_statement;schedule:
AT TIMESTAMP [+ INTERVAL INTERVAL]
| EVERY INTERVAL [STARTS TIMESTAMP] [ENDS TIMESTAMP]INTERVAL:
quantity {YEAR | QUARTER | MONTH | DAY | HOUR | MINUTE |
           WEEK | SECOND | YEAR_MONTH | DAY_HOUR | DAY_MINUTE |
           DAY_SECOND | HOUR_MINUTE | HOUR_SECOND | MINUTE_SECOND}1)首先来看一个简单的例子来演示每秒插入一条记录到数据表USE test;
CREATE TABLE aaa (timeline TIMESTAMP);
CREATE EVENT e_test_insert
ON SCHEDULE EVERY 1 SECOND
DO INSERT INTO test.aaa VALUES (CURRENT_TIMESTAMP);
等待3秒钟后,再执行查询成功。2) 5天后清空test表:CREATE EVENT e_test
ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 5 DAY
DO TRUNCATE TABLE test.aaa;
3) 2007年7月20日12点整清空test表:CREATE EVENT e_test
ON SCHEDULE AT TIMESTAMP '2007-07-20 12:00:00'
DO TRUNCATE TABLE test.aaa;
4) 每天定时清空test表:CREATE EVENT e_test
ON SCHEDULE EVERY 1 DAY
DO TRUNCATE TABLE test.aaa;
5) 5天后开启每天定时清空test表:CREATE EVENT e_test
ON SCHEDULE EVERY 1 DAY
STARTS CURRENT_TIMESTAMP + INTERVAL 5 DAY
DO TRUNCATE TABLE test.aaa;
6) 每天定时清空test表,5天后停止执行:CREATE EVENT e_test
ON SCHEDULE EVERY 1 DAY
ENDS CURRENT_TIMESTAMP + INTERVAL 5 DAY
DO TRUNCATE TABLE test.aaa;
7) 5天后开启每天定时清空test表,一个月后停止执行:CREATE EVENT e_test
ON SCHEDULE EVERY 1 DAY
STARTS CURRENT_TIMESTAMP + INTERVAL 5 DAY
ENDS CURRENT_TIMESTAMP + INTERVAL 1 MONTH
DO TRUNCATE TABLE test.aaa;
[ON COMPLETION [NOT] PRESERVE]可以设置这个事件是执行一次还是持久执行,默认为NOT PRESERVE。
8) 每天定时清空test表(只执行一次,任务完成后就终止该事件):CREATE EVENT e_test
ON SCHEDULE EVERY 1 DAY
ON COMPLETION NOT PRESERVE
DO TRUNCATE TABLE test.aaa;
[ENABLE | DISABLE]可是设置该事件创建后状态是否开启或关闭,默认为ENABLE。
[COMMENT ‘comment’]可以给该事件加上注释。修改事件(ALTER EVENT)
ALTER EVENT event_name
[ON SCHEDULE schedule]
[RENAME TO new_event_name]
[ON COMPLETION [NOT] PRESERVE]
[COMMENT 'comment']
[ENABLE | DISABLE]
[DO sql_statement]
1) 临时关闭事件ALTER EVENT e_test DISABLE;
2) 开启事件ALTER EVENT e_test ENABLE;
3) 将每天清空test表改为5天清空一次:ALTER EVENT e_test
ON SCHEDULE EVERY 5 DAY;删除事件(DROP EVENT)
语法很简单,如下所示:DROP EVENT [IF EXISTS] event_name
例如删除前面创建的e_test事件DROP EVENT e_test;
当然前提是这个事件存在,否则会产生ERROR 1513 (HY000): Unknown event错误,因此最好加上IF EXISTSDROP EVENT IF EXISTS e_test;