请帮忙优化一下sql语句
SELECT   folio.xcode,
              folio.type,
              count(folio.fcode),
              sum(folio.fbprc),
              sum(folio.fser)
    FROM   folio
  WHERE   (folio.fdt   > =   to_date( '2005-02-21 ', 'yyyy-mm-dd '))
      AND   (folio.fdt   <=   to_date( '2005-03-20 ', 'yyyy-mm-dd '))
      AND   (folio.xcode   IN   (SELECT   temp_deparmt.xcode   FROM   temp_deparmt))
  GROUP   BY   folio.xcode,   folio.type
  Order   By   folio.xcode   Asc,   folio.Type   Asc;

其中folio表中有500万条数据，上面的语句执行起来要花费1~2分钟，希望高手们帮忙优化一下。

------解决方案--------------------
folio.type,
count(folio.fcode),
sum(folio.fbprc),
sum(folio.fser)
FROM folio inner join temp_deparmt on folio.xcode=temp_deparmt.xcode
WHERE (folio.fdt > = to_date( '2005-02-21 ', 'yyyy-mm-dd '))
AND (folio.fdt <= to_date( '2005-03-20 ', 'yyyy-mm-dd '))
GROUP BY folio.xcode, folio.type
Order By folio.xcode Asc, folio.Type Asc;
------解决方案--------------------
pl/sql developer里面的右上角的new－> explain plan window窗口

或者后台看执行计划
示例：

SQL> @?/rdbms/admin/utlxplan.sql;

Table created.


SQL> alter session set "_always_semi_join "=off;

Session altered.

SQL> explain plan for
2 select q.id as questionid, q.text as questiontext, q.is_deleted, q.create_date, q.created_by, q.last_update_date, q.last_updated_by, q.image_url, q.image_location, q.category_id, q.allow_html, q.site_id, qbq.question_bank_id, qbq.question_id as qstid
from ilearn.question q,ilearn.question_bank_question qbq,ilearn.response_type rt
where exists
(select 'x '
from ilearn.response_value
where response_value.response_type_id = rt.id and response_value.is_deleted != 'y ') and
q.id = qbq.question_id and
rt.question_id = q.id and
rt.is_deleted != 'y ' and
q.is_deleted != 'y ' and
qbq.question_bank_id = :1 3 4 5 6 7 8 9 10 11 12
13 /

Explained.

SQL> @?/rdbms/admin/utlxpls.sql;

PLAN_TABLE_OUTPUT
----------------------------------------------------------

--------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost |
--------------------------------------------------------
| 0 | SELECT STATEMENT | | 6 | 810 | 142 |
|* 1 | FILTER | | | | |
|* 2 | HASH JOIN | | 6 | 810 | 130 |
| 3 | NESTED LOOPS | | 118 | 14278 | 86 |
|* 4 | TABLE ACCESS FULL | QUESTION | 51988 | 5533K| 86 |
|* 5 | INDEX UNIQUE SCAN | QUESTION_BANK_QUESTION_PK | 1 | 12 | |
|* 6 | TABLE ACCESS FULL | RESPONSE_TYPE | 2599 | 36386 | 43 |