Recid (key) |   ID  |   Date   | Value
1           |   1   | 02.02.11 |   7
2           |   1   | 02.03.12 |   8
3           |   1   | 02.04.13 |   0
4           |   1   | 02.05.14 |   2
5           |   2   | 02.01.12 |   8
6           |   2   | 02.02.13 |   0
7           |   3   | 02.02.13 |   2
8           |   3   | 02.03.14 |   2
9           |   3   | 02.05.14 |   0

SELECT COUNT(*) FROM table t WHERE t.Date = "03.05.13" AND t.Value>0 GROUP BY t.ID

select top 1 count(distinct id) from some_table where date <= @limit group by date order by date desc