row_number() over(partition by '分组' order by '日期')

实例1

create table gao (id int ,date1 datetime,zhi NUMERIC(12,3))

---drop table gao

insert into gao values(1,'2016-5-3 00:12:00',60.2)

insert into gao values(2,'2016-4-3 00:12:00',90.2)

insert into gao values(3,'2016-3-3 00:12:00',70.2)

insert into gao values(3,'2016-6-3 00:12:00',60.2)

insert into gao values(4,'2016-7-3 00:12:00',30.2)

insert into gao values(4,'2016-8-3 00:12:00',30.2)

select id,date1,zhi,rownum from (

select row_number() over(partition by id order by date1 ) as rownum, * from gao

) t where t.rownum=1

----------------------

select * from

(

select row_number() over(partition by '分组' order by '日期') as rownum -- 排序并分组

, * -- 所需显示的字段

from 表

) as T

where T.rownum = 1

对每组的数据按日期排序并加上行号

取出时只取行号为1，也就是第一条数据。