SELECT top(1) [ACTIVITIES.StartDateTime]
	,ACTIVITIES.CategoryId
        ,ACTIVITIES.Id 
	
  FROM [Activities]

order by [ACTIVITIES.StartDateTime] desc

DECLARE @tDUMMY TABLE (
  StartDate DATE,
  Activity VARCHAR(100),
  CategoryID INT
);

INSERT INTO @tDUMMY

SELECT CONVERT(DATE, '1876-01-01'), 'Action in 1876', 1 UNION ALL
SELECT CONVERT(DATE, '1945-01-01'), 'Action in 1945', 1 UNION ALL
SELECT CONVERT(DATE, '2000-01-01'), 'Chaos', 2 UNION ALL
SELECT CONVERT(DATE, '2010-10-15'), 'Stare at wall', 3 UNION ALL
SELECT CONVERT(DATE, '2010-10-16'), 'Unknown', 3 UNION ALL
SELECT CONVERT(DATE, '2012-01-01'), '????', 4 UNION ALL
SELECT CONVERT(DATE, '4712-01-01'), 'Faraway', 4

;


SELECT StartDate, Activity, CategoryID FROM
(
   SELECT StartDate, Activity, CategoryID, 
   ROW_NUMBER() over (partition by CategoryID ORDER BY StartDate DESC)ORDERING FROM @tDUMMY
) tmp
WHERE tmp.ORDERING = 1 ORDER BY 1