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CBO Query re-write [message #540322]

Sat, 21 January 2012 23:56

manubatham20
Messages: 566
Registered: September 2010
Location: Seattle, WA, USA

Senior Member

Hi,

My question is regarding the working of CBO.

While executing a query, CBO generates an explain/execution plan for the query. Does CBO does the work of query re-write to optimize it? If yes, can I get the query re-written by CBO?

Thanks!!
Manu

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Re: CBO Query re-write [message #540327 is a reply to message #540322]

Sun, 22 January 2012 00:38

Michel Cadot
Messages: 68641
Registered: March 2007
Location: Nanterre, France, http://...

Senior Member
Account Moderator

Quote:

Does CBO does the work of query re-write to optimize it?

Yes.

Quote:

If yes, can I get the query re-written by CBO?

You can't. It may rewrite it in a way that is not in the SQL syntax and is stored in any place (in clear, it is stored in a binary format as the execution plan).

Regards
Michel

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Re: CBO Query re-write [message #540328 is a reply to message #540327]

Sun, 22 January 2012 00:40

Michel Cadot
Messages: 68641
Registered: March 2007
Location: Nanterre, France, http://...

Senior Member
Account Moderator

You may read:
Database Performance Tuning Guide
Chapter 13 The Query Optimizer
Section 13.4 Understanding the Query Optimizer

Regards
Michel

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