MySQL：如何每小时对数据进行分组并获得最新的小时数

SELECT  f.*
FROM    (
        SELECT  MAX(UNIX_TIMESTAMP(date_created)) AS mts
        FROM  user_accounts 
        GROUP BY HOUR(date_created)
        ) s
JOIN    user_accounts  f
ON      UNIX_TIMESTAMP(date_created) = s.mts
WHERE  DATE(date_created) = \'2009-10-27\'

SELECT userid, username, date_created
FROM user_accounts 
WHERE userid IN (
  SELECT MAX(userid)
  FROM user_accounts 
  WHERE date_created >= \'2009-10-27 00:00:00\' AND date_created < \'2009-10-27 23:59:59\'
  GROUP BY HOUR(date_created)
)

select STRAIGHT_JOIN
       ui.userid,
       ui.username,
       ui.date_created
   from 
       ( select
               date( date_created ),
               hour( date_created ),
               max( date_created ) as LastPerHour
            from
               user_accounts
            where
               date( date_created ) = \'2009-10-27\'
            group by
               date( date_created), 
               hour( date_created )) PreQuery
      join user_accounts ui
         on PreQuery.LastPerHour = ui.date_created

SELECT userid, username, date_created
FROM user_accounts 
WHERE HOUR(date_created) = (SELECT HOUR(date_created) FROM user_accounts ORDER BY date_created DESC LIMIT 1);

select date(PROCESS_DATE),hour(PROCESS_DATE),EVENT,COUNT(*) from statistics group by EVENT,date(PROCESS_DATE),time(PROCESS_TIME) order by 1 desc, 2 desc limit 1;