在线等一个sql语句的优化问题
select info_information.id,info_title,class_b,mode, 'price '=case when price=0 then '面谈 ' when price <> 0 then price+ '元 ' end,city,pubdate,scannums from info_information,info_class_b,info_mode where info_class_b.id=class_bid and info_mode.id=modeid and class_bid in (select id from info_class_b where class_aid=@class_aid ) and modeid=@modeid order by istop desc,pubdate desc
数据表中有20万条数据，查询性能很差，希望高手们能给出优化的建议，还有怎么样建立索引能提高查询速度？

[解决办法]
select info_information.id,
info_title,
class_b,
mode,
'price '=case when isnull(price,0)=0 then '面谈 ' else price+ '元 ' end,--改为else就可以判断了
city,pubdate,
scannums
from info_information,info_class_b,info_mode
where info_class_b.id=class_bid
and info_mode.id=modeid
--这句去掉,加在下面where中了
--and class_bid in (select id from info_class_b where class_aid=@class_aid )
and modeid=@modeid
and info_class_b.class_aid=@class_aid
order by istop desc,pubdate desc
[解决办法]
把各字段所属的表标明一下，总的来说感觉用
select ..from
info_class_b as tb1
inner join
info_class_b as tb2
on tb1.class_aid=@class_aid
and tb1.id=tb2.class_bid
..