select *
from tb t
where exists (select 1 from tb where 往来单位=t.往来单位 and 物料=t.物料 and 单价<>t.单价)

------解决方案--------------------
SQL code
select * from tb t where
 exists (select 1 from tb where 往来单位=t.往来单位 and 物料=t.物料 having count(1)>1)

------解决方案--------------------
SQL code

select * from tb t where
 exists (select 1 from tb where 往来单位=t.往来单位 and 物料=t.物料 group by 往来单位,物料 having count(1)>1)