SELECT 5 most recent SQL Server

Question

I have a table with records like this:

id        timestamp               dose             drug_id
1     2012-10-04 09:10:54          05                 2
1     2012-10-04 09:12:34          15                 2
1     2012-10-04 09:15:12          20                 2
1     2012-10-04 09:35:32          25                 2
1     2012-10-04 09:37:34          25                 2
1     2012-10-04 09:39:24          25                 2
1     2012-10-04 09:42:16          35                 2
1     2012-10-04 09:43:07          35                 2

What I want to do is select the last 5 used dose values for a given drug, so in this case the query should return 35, 25, 20, 15, 05.

I know I can use TOP and ORDER BY to get the latest 5 entries, but in this case it would return duplicates (35, 35, 25, 25, 25).

What should I use to get the output I want?

Answer 1

I don't have access to my server to test this, but should not

SELECT TOP 5 dose 
FROM table_id 
GROUP BY dose 
ORDER BY max(time) desc;

work?

EDIT: Tested on http://sqlfiddle.com/#!6/610c4/2, note that I haven't used timestamp merely time. Fix appropriately.