DateTime group by date and hour

Question

I have a datetime called activity_dt and the data looks like this:

2/5/2013 9:24:00 AM
2/7/2013 7:17:00 AM

How do i group

Answer 1

SELECT [activity_dt], COUNT(*) as [Count]
  FROM 
 (SELECT dateadd(hh, datediff(hh, '20010101', [activity_dt]), '20010101') as [activity_dt]
    FROM table) abc
 GROUP BY [activity_dt]