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Time taken for execution of SQL Query in DB2 program

 
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arultm

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Joined: 03 Dec 2007
Posts: 7
Location: Mumbai

PostPosted: Mon Dec 03, 2007 4:35 pm    Post subject: Time taken for execution of SQL Query in DB2 program
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Hi,



If we use more conditions in WHERE clause to restrict number of rows to be fetched, will the execution of query take more time?



For ex.



1.)SELECT data1

FROM table

WHERE data2 = ‘V’

AND data3 = ‘101’



2.) SELECT data1

FROM table

WHERE data2 = ‘v’

AND data3 = ‘101’

AND data4 = ‘k’



While executing both the queries in a program using cursor, will 2nd query takes more time for execution when compared to 1st query?

Please clarify….
And please give some tips to use SQL query efficiently in the program...
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dick scherrer

Site Director


Joined: 23 Nov 2006
Posts: 19270
Location: Inside the Matrix

PostPosted: Mon Dec 03, 2007 8:58 pm    Post subject:
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Hello arultm and welcome to the forums,

Quote:
If we use more conditions in WHERE clause to restrict number of rows to be fetched, will the execution of query take more time?

It should not take more time.

Quote:
While executing both the queries in a program using cursor, will 2nd query takes more time for execution when compared to 1st query?

No.

Quote:
And please give some tips to use SQL query efficiently in the program...

Whenever possible, use columns that are indexed. Dependig on the type of queries, it is often necessary to add additional indexes to support the queries.
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Craq Giegerich

Senior Member


Joined: 19 May 2007
Posts: 1512
Location: Virginia, USA

PostPosted: Mon Dec 03, 2007 9:19 pm    Post subject: Re: Time taken for execution of SQL Query in DB2 program
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arultm wrote:
Hi,

1.)SELECT data1
FROM table
WHERE data2 = ‘V’
AND data3 = ‘101’


2.) SELECT data1
FROM table
WHERE data2 = ‘v’
AND data3 = ‘101’
AND data4 = ‘k’



While executing both the queries in a program using cursor, will 2nd query takes more time for execution when compared to 1st query?

Please clarify….


I am assuming that with the first cursor your program is checking data4, so what you have done is move some of the processing from your program to DB2.
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TG Murphy

Active User


Joined: 23 Mar 2007
Posts: 149
Location: Ottawa Canada

PostPosted: Mon Dec 03, 2007 9:42 pm    Post subject:
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If your first query returns 10,000 rows and your second query reduces this to 500 rows then your second query should execute faster. Your COBOL program will do 500 fetches instead of 10,000.

The DBAs always answer these questions with "It all depends..."
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Gnanas N

Active Member


Joined: 06 Sep 2007
Posts: 788
Location: Chennai, India

PostPosted: Mon Dec 03, 2007 9:49 pm    Post subject:
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I think 2nd query will run faster than first query. Because in 2nd query DATA2, DATA3 and DATA4 are colunms used for restricting the fetching. And I assume those 3 colums are indexes.

You can use EXPLAIN PLAN to get the details for Execution.

You please visit this link for DB2 tuning.

http://www.ibm.com/developerworks/db2/library/techarticle/dm-0404mcarthur/index.html

Correct me if I am wrong.
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arultm

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Joined: 03 Dec 2007
Posts: 7
Location: Mumbai

PostPosted: Tue Dec 04, 2007 9:37 am    Post subject: Reply to: Time taken for execution of SQL Query in DB2 progr
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Hi
Thank you very much..
It is really helpful and will let you know how it is working after executing it..
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