Id,    Date,        Param1,   Param2,   Norma
1,  "01.01.2010",   15,       100,       0.95
2,  "02.01.2010",   18,       200,       0.97
3,  "02.01.2010",   22,       150,       0.94
4,  "03.01.2010",   19,       200,       1.01
5,  "03.01.2010",   14,       220,       0.95
6,  "05.01.2010",   18,       160,       1.05
7,  "05.01.2010",   24,       400,       1.01
8,  "05.01.2010",   20,       220,       0.98

Id,    Date,        Param1,     Param2, Norma
1,  "01.01.2010",    15,        100,      0.95
2,  "02.01.2010",    18,        200,      0.97
4,  "03.01.2010",    19,        200,      1.01
7,  "05.01.2010",    24,        400,      1.01

select q.id, q.dta, q.tme, q.param1, q.param2, q.norma from
(
  select t.id as id, cast(t.tme as date) as dta, cast(t.tme as time) as tme, t.param1 as param1, t.param2 as param2, t.norma as norma,
  row_number() over (partition by cast(t.tme as date) order by abs(t.norma-1.000)) as r_n
  from tst t
  where t.a_id = 1
) q
where q.r_n = 1

select t1.id as id,  cast(t1.tme as date) as dta, cast(t1.tme as time) as tme, t1.param1 as param1, t1.param2 as param2, t1.norma
from tst t1
join
(
  select cast(t2.tme as date) as dta, min(abs(t2.norma-1.000)) as delta
  from tst t2 where t2.a_id = 1
  group by 1
) j
on cast(t1.tme as date) = j.dta and abs(t1.norma-1.000)=j.delta
where t1.a_id = 1
order by 1