Sowmya Shankark

 UPDATE outputtable,
       (SELECT Sum(total)  SUM,
                Year(date)  year,
                Month(date) month,
                Day(date)   day,
                Hour(date)  hour
         FROM   inputtable
         GROUP  BY Year(date),
                   Month(date),
                   Day(date),
                   Hour(date)) InputT SET    total = InputT.sum WHERE  Year(outputtable.date) = InputT.year
        AND Month(outputtable.date) = InputT.month
        AND Day(outputtable.date) = InputT.day
        AND Hour(outputtable.date) = InputT.hour;