SQL语句优化求助 - MS-SQL Server / 疑难问题

我这有一段语句:  
select a.aaid,amount,b.exit_amount  
from (select id,object_id,amount,price,date1 from AA where date1 BETWEEN '20100401' AND '20100430' ) a 
  LEFT JOIN
  (SELECT aa_id, isnull(SUM(exit_amount), 0) AS exit_amount from AA_Exit GROUP BY aa_id) b ON a.id = b.yz_id

   
现在有个问题:
AA这个表有40万条数据,现在我用左连接,语句如上,这样执行要15秒时间.但如果改成如下语句,就只要1秒钟.
select a.aaid,amount
from (select id,object_id,amount,price,date1 from AA where date1 BETWEEN '20100401' AND '20100430' ) a 
  LEFT JOIN
  (SELECT aa_id, isnull(SUM(exit_amount), 0) AS exit_amount from AA_Exit GROUP BY aa_id) b ON a.id = b.yz_id

但我现在必须要用上面这条语句执行.该如何优化.

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一样？》

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create index ix_aa_id on AA_Exit(aa_id)建索引 试一下

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第二次1秒是因为直接从BUFFER CACHE取的原因吧,没有理由两个相差这么大.
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