select v.aid,d.name,mrn,pn,ptime,opponame,v.note,op, sum(quan*pri)as 进价,sum(quan*prr)as 售价,sum((prr-pri)*quan) as 差价 from 

vw_mr_ou v

inner join tb_pub_dept d on d.aid=v.aid and d.id=v.mrn and d.typ=8

INNER JOIN tbl_id_item i on i.item=v.sty

where v.aid=${aid} and mrn in (${mrn})

and ptime>='${bdt}' and ptime<'${edt}' and ( '${oppo}'='' or (v.oppo<>'' and v.oppo  in ('${oppo}')))and ('${drugtyp}'=''or (v.sty<>'' and v.sty in ('${drugtyp}')))

group by  v.aid,mrn,pn,ptime,opponame,op,v.note,d.name

在这个语句中，${oppo}和${drugtyp}会返回多个结果，但是如果把下拉框中的条件全部选中，查询结果为空，如果全部不选，就可以正常出结果，这是为什么？