select * from 
(  SELECT [Year]
         ,[Type]
         ,[Category]
         ,[AnnualCost]
         ,[TimeStamp] as MaxTimeStamp
         ,row_number() over (partition by [Year], [Type], [Category] order by [TimeStamp] desc ) as rn 
     FROM [PromOneSite].[Budgeting].[MISBasePrice]
    where Year = 2016
      and category IN ('Leasing Office Desktop')
      and TimeStamp IS Not Null 
) tt
where tt.rn = 1