oracle使用索引和不使用索引时的性能对比

SELECT *

  FROM (SELECT ROW_.*, ROWNUM ROWNUM_

          FROM (SELECT *

                  FROM KQS_SQ_INFO i 

                 ORDER BY i.EMP_ID desc ) ROW_

         WHERE ROWNUM <= 20)

 WHERE ROWNUM_ >= 10;

explain plan for SELECT *

  FROM (SELECT ROW_.*, ROWNUM ROWNUM_

          FROM (SELECT *

                  FROM KQS_SQ_INFO i 

                 ORDER BY i.EMP_ID desc ) ROW_

         WHERE ROWNUM <= 20)

 WHERE ROWNUM_ >= 10;

select * from TABLE(dbms_xplan.display);打印出性能分析表