oracle统计无记录时，写默认值

select  nvl(max(t1.packagesize),0)  

from (

        select decode(count(t.per_bus_code),0,'1') per_bus_code,decode(count(t.buss_code),0,'1') buss_code,decode(count(t.per_code),0,'1') per_code 

           from t_tybook_back_pers_business t

           where t.per_code = 'TY-00000106' 

           and t.end_date > sysdate 

           and t.start_date<=sysdate ) t

left join t_tybook_before_business t1 on t.buss_code = t1.code 

group by t.per_code;