select t.real_ammeter, t.eng_region_id,a.region_name, b.device_name,t.occur_time,b.eng_device_id,b.eng_type_id
from ammeter t
inner join eng_region a on a.eng_region_id =t.eng_region_id
inner join eng_device b on b.eng_region_id =t.eng_region_id
--这里的查询条件应该用where
where b.eng_type_id =109
and to_char (t.occur_time,'yyyy-mm-dd')='2011-06-02'
order by t.real_ammeter desc;
也有可能是t里面的一条记录对应多条a或b的记录,所以相同的t的信息有多条