请各位大虾帮忙看看这条指令有没有优化的空间~

现在执行一次大概要1秒，生产环境每次执行需要循环传值，大概循环执行几百次..

数据量说明：a表60万  b表180万  e表260万

SELECT cucy,up,qty,signdat 

FROM 

  (

    select 

    nvl(a.cucy,a.qpcucy) cucy, 

    nvl(b.ytxup,b.qpytxup) up ,

    NVL(b.cprqty,b.caqqty) qty,

    a.signdat,a.vndno 

    from txf000hfc21 a,txf000hfc22 b,txf000hba32 e

    where a.purco=b.purco and a.purshno= b.purshno and a.vndno=b.vndno AND a.purco=e.purco AND a.purshno=e.purshno AND b.puritm=e.puritm

    and  a.purco='5' and Nvl(b.ordhmat,e.mtno)='A2P1P34400019WA7'  AND a.rckmk='Y'

    ORDER BY a.signdat desc, up,qty

  ) 

WHERE ROWNUM=1;





执行计划：

Plan hash value: 3415185491                                                                                 

                                                                                                            

------------------------------------------------------------------------------------------------------------

| Id  | Operation                       | Name             | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |

------------------------------------------------------------------------------------------------------------

|   0 | SELECT STATEMENT                |                  |     1 |    38 |       |  8428   (1)| 00:01:42 |

|*  1 |  COUNT STOPKEY                  |                  |       |       |       |            |          |

|   2 |   VIEW