1.查看事件是否开启
show variables like '%sche%';2off的话，则开启事件
set global event_scheduler =1;3创建存储过程
CREATE PROCEDURE book ()
update car_space SET start_time =null , space_status=0 WHERE minute(timediff(now(),start_time))>15 and space_status=1;
4创建事件event ，解释：每30s执行一次存储过程book预定，对car_space表中的已经超过预定时间15min的数据进行恢复。
create event if not exists e_book
on schedule every 30 second
on completion preserve
do call book(); 5关闭event
alter event e_book ON
COMPLETION PRESERVE DISABLE; 6开启事件
alter event e_book ON
COMPLETION PRESERVE ENABLE;
