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https://issues.apache.org/jira/browse/DERBY-6938?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16045796#comment-16045796
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Bryan Pendleton commented on DERBY-6938:
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I'm not certain I understand the question. I suspect we may have to study the
code, and perform some experiments, to determine the answer.
But we can start by looking at these resources, in addition to the
documentation you mentioned:
* https://wiki.apache.org/db-derby/LanguageOptimize
* http://db.apache.org/derby/papers/optimizer.html
I looked at the explain.txt that you attached, but I'm not certain I am
following your analysis.
I wonder if you might be able to annotate the explain.txt with your own
comments, and point directly at the section of the explain output that is of
particular interest to you, so that I can better understand the question you
are asking.
Note that it is entirely possible that Derby's query optimizer is not as
sophisticated as you think it may be. That is one of the reasons that this
testing is so important: we need to understand where Derby's query optimizer is
not considering all the information that is available to it when it makes its
decisions.
> Obtain cardinality estimates and true estimates for base tables as well as
> for intermediate results for queries involving multiple joins.
> -------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: DERBY-6938
> URL: https://issues.apache.org/jira/browse/DERBY-6938
> Project: Derby
> Issue Type: Sub-task
> Components: SQL
> Reporter: Harshvardhan Gupta
> Assignee: Harshvardhan Gupta
> Attachments: explain.txt
>
>
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