oracle top 10 sql

--top 10 sql
SELECT   *
    FROM (SELECT   b.username username,
                     a.disk_reads
                   / DECODE (a.executions, 0, 1, a.executions) rds_exec_ratio,
                   a.sql_text STATEMENT
              FROM v$sqlarea a, dba_users b
             WHERE a.parsing_user_id = b.user_id AND b.username = 'ZYK'
          ORDER BY rds_exec_ratio DESC)
   WHERE ROWNUM < 11
ORDER BY rds_exec_ratio DESC