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MySQL的计划任务创建
实际项目中只想将最近7天的记录保存在MySQL数据库中，使用程序通过SQL指令的方式删除比较麻烦且效率低，用Mysql 提供的事件调度器（event scheduler)可轻松实现。
具体步骤如下：
1：超级用户方式登陆MySQL console
# mysql -uroot
2：打开event_scheduler(默认是关掉的）
mysql> set global event_scheduler = ON;
3：创建我们的事件（本例中命名为delete_old_record)
mysql> CREATE EVENT delete_old_record
ON SCHEDULE EVERY 1 DAY STARTS NOW()
DO
-- delete the old records of demo_1_table
DELETE FROM demo_1_table WHERE datediff(NOW(),log_timestamp)>=7;
-- delete the old records of puma_2_table
DELETE FROM demo_2_table WHERE datediff(NOW(),log_timestamp)>=7;
-- delete the old records of puma_3_table
DELETE FROM demo_3_table WHERE datediff(NOW(),log_timestamp)>=7;
-- delete the old records of puma_4_table
DELETE FROM demo_4_table WHERE datediff(NOW(),log_timestamp)>=7;
4：启动创建的事件
mysql> ALTER EVENT delete_old_record ENABLE;
这样以后，数据库就会每天执行DO后面的作业，删除各个table中7天之前的记录。
附录：CREATE EVENT的格式如下：
CREATE
[DEFINER = { user | CURRENT_USER }]
EVENT
[IF NOT EXISTS]
event_name
ON SCHEDULE schedule
[ON COMPLETION [NOT] PRESERVE]
[ENABLE | DISABLE | DISABLE ON SLAVE]
[COMMENT 'comment']
DO event_body;
schedule:
AT timestamp [+ INTERVAL interval] ...
| EVERY interval
[STARTS timestamp [+ INTERVAL interval] ...]
[ENDS timestamp [+ INTERVAL interval] ...]
interval:
quantity {YEAR | QUARTER | MONTH | DAY | HOUR | MINUTE |
WEEK | SECOND | YEAR_MONTH | DAY_HOUR | DAY_MINUTE |
DAY_SECOND | HOUR_MINUTE | HOUR_SECOND | MINUTE_SECOND}
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