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Improve the performance of SELECT query

 
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rahul_desai29

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Joined: 15 Mar 2006
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PostPosted: Tue Mar 21, 2006 11:55 am    Post subject: Improve the performance of SELECT query
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SELECT * it is running very slow,how you will make it faster?
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priyesh.agrawal

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Joined: 28 Mar 2005
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PostPosted: Tue Mar 21, 2006 12:58 pm    Post subject: Re: Improve the performance of SELECT query
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SELECT * it is running very slow,how you will make it faster?

By coding only your columns of interest.

Regards,
Priyesh.
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KS

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PostPosted: Wed Mar 22, 2006 12:14 pm    Post subject:
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Hi,
It is not the correct standard to give a select a query with *.This statement will result in excessive I/O overhead.
1. Instead of '*' , give the column names on which u need to select
2. Give necessary where clause
3. If u r tring to fetch rows from a larger db , thenuse FETCH FIRST 100 ROWS ONLY;
ex-
SELECT TRANS_NO , ST_DATE FROM EMPLOYEE.TABLE1
WHERE TRANS_NO = 7458959
ORDER BY TRANS_NO DESC
FETCH FIRST 100 ROWS ONLY ;

Thanks,
Ks
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Gautam512

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Joined: 05 Oct 2005
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PostPosted: Wed Mar 22, 2006 3:47 pm    Post subject: Re: Improve the performance of SELECT query
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i totally accept what KuttiSatha said,

Select * always increases the I/O overhead.

Better to give the required column names.

One more important thing which increases the efficiency is,

for every column in a table there will be assigned indices (order of preference) if u use the same order for the column selected in the select query u'll surely increase the efficiency.
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priyesh.agrawal

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Joined: 28 Mar 2005
Posts: 1452
Location: Chicago, IL

PostPosted: Wed Mar 22, 2006 4:15 pm    Post subject: Re: Improve the performance of SELECT query
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You may also want to code "FOR FETCH ONLY" to improve preformance, in case your query is read-only.

Regards,
Priyesh.
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