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Re: Explain the order of query
Posted by: Jørgen Løland
Date: March 28, 2012 05:06AM

Hi Jongse,

From the information you have provided it's not possible to say in which order these tables are accessed/subqueries executed. The only thing that is certain is that T1 is accessed before T2 because of the relative order within the query block (i.e., same id=1).

Depending on the query, query blocks 2, 3 and 4 may be executed before T2 is joined with T1. Thus, not only "1-1-2-3-4" and "1-1-4-2-3" is possible, but maybe even "1-2-3-4-1" and all similar permutations.

I believe you have these choices at the moment:
* provide the information Rick has requested (SHOW CREATE TABLE, the query etc)
and thus give us an opportunity to answer
* download MySQL 5.6 and use optimizer tracing to see the actual execution order
* get a support deal and provide them with the info you have
* accept that you won't get an answer to this :-(

For optimizer tracing, see here

Hope this helps,
Jørgen Løland
Software Engineer, MySQL, Oracle
jorgenloland.blogspot.com

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