declare @t table (id int identity(1,1),d date,t varchar(10));
insert into @t select '2012-07-01','aa' union all
select '2012-07-01','bb' union all
select '2012-07-02','cc' union all
select '2012-07-01','dd' union all
select '2012-07-20','xx';

select * from (
    select rn=ROW_NUMBER() over(partition by d order by id),* from @t 
) x where x.rn in (1,2)
/*
rn                   id          d          t
-------------------- ----------- ---------- ----------
1                    1           2012-07-01 aa
2                    2           2012-07-01 bb
1                    3           2012-07-02 cc
1                    5           2012-07-20 xx
*/
--你看是不是要这种，每一天前两条。

------解决方案--------------------
SQL code
;with cte as(
  SELECT *
  FROM xingzheng_daiban_shixiang 
  WHERE (DATEPART(yy, riqi) = '2012') AND (DATEPART(mm, riqi) = '7')
)

SELECT id, CONVERT(varchar, DATEPART(dd, riqi)) AS nDay, biaoti,riqi
FROM cte T
WHERE id IN (SELECT top 2 id FROM cte WHERE riqi=T.riqi order by id) 
ORDER BY riqi