mysql触发器的使用

语法：

create trigger 触发器名 before(或者after) update（或者delete或者insert）on 数据库表名
for each row(固定结构)
begin
　　sql语句
end 

实例：

  create trigger calculate_fileSize after update on dps_task

　for each row

BEGIN
IF new.is_finish = 1 and new.doc_type = 379 THEN
           UPDATE dps_resource SET filesize = (SELECT SUM(filesize) 
           from dps_resource_associate dra WHERE dra.resource_id = 
           new.resource_id and dra.uri like "%/pic/%") WHERE 
           dps_resource.id = new.resource_id;
ELSEIF new.is_finish = 1 and new.doc_type <> 51 THEN
           UPDATE dps_resource SET filesize = (SELECT SUM(filesize) 
           from dps_resource_associate dra WHERE dra.resource_id = 
           new.resource_id and dra.uri like "%/origpic/%") WHERE 
           dps_resource.id = new.resource_id;
END IF;
END;        

new: 指的是sql中更新后的那条数据

old：指的是sql中更新前的那条数据

如果事件是delete，则只有old没有new。如果事件是insert, 则只有new没有old，否则会报错。