Most used or executed SQL Queries ( Last 20 )

Q: How can i see most used or executed SQL Queries ?

SELECT *
  FROM (  SELECT ss.sql_text,
                 a.SQL_ID,
                 SUM (CPU_TIME_DELTA),
                 SUM (DISK_READS_DELTA),
                 COUNT (*)
            FROM DBA_HIST_SQLSTAT a, dba_hist_snapshot s, v$sql ss
           WHERE     s.snap_id = a.snap_id
                 AND a.sql_id = ss.sql_id
                 AND s.begin_interval_time > SYSDATE - 1
        GROUP BY ss.sql_text, a.SQL_ID
        ORDER BY SUM (CPU_TIME_DELTA) DESC)
 WHERE ROWNUM <= 20;