mysql procedure-关于mysql5.6存储与游标的问题

如下是我的过程,不解的是当我把从游标里的任何一列当做判断结束游标条件时，无论何时它都为空,但它确确实实可以循环完，百思不得其解。
例如 while ( type is not null ) 。 这里的type永远都为空。
再如果我将任意一列 , event_value 当做while 条件 event_value 同样为空。
在此跪求大鸟解答了。
delimiter $$
create procedure test( in event_value_name varchar(20) , in datestr varchar(20) , in start_date datetime , in end_date datetime )
begin
declare temp varchar(10) default "";
declare temps varchar(200) default "";
declare report_tim varchar(100) default "";
declare type varchar(50);
declare event_value varchar(50);
declare source varchar(50);
declare event_name varchar(50);
declare cot varchar(50);
declare allrow cursor for select tev.event_value,tev.source,tev.event_name,count(*) as cot,tev.type,date_format(tev.report_time,'%y-%m-%d') report_tim from ts_event_value tev

where tev.name=event_value_name and tev.report_time between start_date and end_date
group by tev.event_value,tev.source,tev.event_name,tev.type,report_tim order by cot desc limit 15 ;
declare continue handler for not found set type = null;
open allrow;
/*allrowloop:loop*/
fetch allrow into event_value,source,event_name,cot,type,report_tim;
if datestr = "all" then

        WHILE ( TYPE IS NOT NULL ) DO            SELECT s.name INTO temp FROM statistical s WHERE s.name = event_value_name AND s.source = source AND s.event_name = event_name AND s.event_value = event_value AND s.zt = "all";                IF temp = "" OR temp IS NULL THEN                    INSERT INTO statistical VALUES (source,event_name,event_value,COT,event_value_name,report_tim,"all");                ELSE                    UPDATE statistical s SET s.cot = s.cot + COT WHERE s.name = event_value_name AND s.source = source AND s.event_name = event_name AND s.event_value = event_value AND s.zt = "all";                END IF;            FETCH allrow INTO event_value,source,event_name,COT,TYPE,report_tim;        END WHILE;    END IF;     COMMIT;    SELECT event_value,source,event_name,COT,temp;    /*SELECT temps;*/    /*END LOOP allrowloop;*/CLOSE allrow;

END;
$$
DELIMITER ;