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
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}