UPDATE @EntityDateTimes SET EventID=(SELECT TOP 1 EventID FROM tkEntityHistory ) WHERE EntityID=@EntityDateTimes.EntityID AND [DateTime]=@EntityDateTimes.[DateTime])
UPDATE @EntityDateTimes SET EventID=(SELECT TOP 1 EventID FROM tkEntityHistory WHERE EntityID=E.EntityID AND [DateTime]=E.[DateTime])FROM @EntityDateTimes E
UPDATE @EntityDateTimes SET EventID=(SELECT TOP 1 EventID FROM tkEntityHistory WHERE EntityID=@EntityDateTimes.EntityID AND [DateTime]=@EntityDateTimes.[DateTime])
UPDATE @EntityDateTimes SET EventID= EH.EventID FROM @EntityDateTimes E INNER JOIN tkEntityHistory EH ON E.EntityID=EH.EntityID AND E.[DateTime]=EH.[DateTime]