1時間あたりの日時のカウントによるSQLServerグループ？

これはどう？ SQL Server 2008を想定：

SELECT CAST(StartDate as date) AS ForDate,
       DATEPART(hour,StartDate) AS OnHour,
       COUNT(*) AS Totals
FROM #Events
GROUP BY CAST(StartDate as date),
       DATEPART(hour,StartDate)

2008年以前の場合：

SELECT DATEADD(day,datediff(day,0,StartDate),0)   AS ForDate,
       DATEPART(hour,StartDate) AS OnHour,
       COUNT(*) AS Totals
FROM #Events
GROUP BY CAST(StartDate as date),
       DATEPART(hour,StartDate)

これにより、次のようになります：

ForDate                 | OnHour | Totals
-----------------------------------------
2011-08-09 00:00:00.000     12       3