AWRから待機イベントクラス別DB時間を時系列グラフ化

AWR(DBA_HIST*)から待機イベントクラス別のDB時間を抽出して時系列グラフにしたときのSQL。
かなり力技・・・

SELECT  runtime     ,
        e.wait_class,
        SUM(e.time_waited)
FROM
        (
                SELECT  e1.snap_id        ,
                        e1.dbid           ,
                        e1.instance_number,
                        e1.EVENT_NAME     ,
                        e1.wait_class     ,
                        (e1.TIME_WAITED_MICRO-e2.time_waited_micro)/1000000 "TIME_WAITED"
                FROM    dba_hist_system_event e1,
                        dba_hist_system_event e2
                WHERE   e1.snap_id            =e2.snap_id+1
                        AND e1.dbid           =e2.dbid
                        AND e1.instance_number=e2.instance_number
                        AND e1.event_id       =e2.EVENT_ID
                        AND e1.DBID           =:dbid
                        AND e1.wait_class    !='Idle'
        ) e,
        (
                SELECT  snap_id        ,
                        dbid           ,
                        instance_number,
                        TO_CHAR(BEGIN_INTERVAL_TIME, 'YY-MM-DD HH24:MI:SS') runtime
                FROM    dba_hist_snapshot
                WHERE   DBID                    =:dbid
                        AND begin_interval_time > :start_time
                        AND begin_interval_time < :end_time
                ORDER BY snap_id DESC
        ) s
WHERE   e.snap_id            =s.snap_id
        AND e.dbid           =s.dbid
        AND e.instance_number=s.instance_number
GROUP BY runtime,
        wait_class
ORDER BY runtime