ORACLE分组取第一条记录

select 查询内容 from
(
select row_number() over(partition by 分组字段 order by 排序字段) as rn , 查询字a,查询字段b..
from  表1,表2 where 条件
) where rn = 1 ;

select 查询内容 from
(
select row_number() over(partition by 分组字段 order by 排序字段) as xuhao , 查询字a,查询字段b..
from  表1 left join 表2 on 条件
) where xuhao = 1 ;