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Explain Utility

 
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Prabha
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Joined: 05 Dec 2005
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PostPosted: Fri Jul 09, 2010 2:43 pm    Post subject: Explain Utility
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Hi,

could you pleae let me know the usage of EXPLAIN utility and where we are handling?

Regards,
Prabha
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dbzTHEdinosauer

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Joined: 20 Oct 2006
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PostPosted: Fri Jul 09, 2010 2:52 pm    Post subject:
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5.58 EXPLAIN SQL REFERENCE

6.4 Chapter 6-4. Using EXPLAIN to improve SQL performance SQL Appl Programmers guide

also, talk to your db2 support to determine what facilities already exist.
it may be that your site has VISUAL Explain.
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LearningDb2

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PostPosted: Fri Jul 09, 2010 5:31 pm    Post subject:
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Hi Prabha,

We use Explain to collect the information abt the access path used by the optimizer for the statement which is explainable.
Suppose you have a stored procedure having hundred's of SQL statements.Then u can use Explain for the sql's whose access path u want to see.Eg:- whether the predicates that u have specified in the select clause are using proper indexes or not.

We assign a query number through which we identify that statement in user created PLAN_TABLE.

Eg-: exlpain all set query number = nn for select.......(explainable statement)

All the informations derived by the Explain are stored in PLAN_TABLE.
Usually GroupID.PLAN_TABLE.

For the description of the columns of Plan_table you can hv a look at SQL reference(Statements-Explain).

Hope this Helps.

Thanks
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