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https://issues.apache.org/jira/browse/DERBY-6004?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13503794#comment-13503794
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Rick Hillegas commented on DERBY-6004:
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One issue we would want to consider is what to do if the table function lies.
With restricted table functions, the restriction is redundantly applied by
Derby outside the table function, so Derby returns correct results even when
the table function lies. However, part of what we want to achieve with ordered
results is to eliminate unnecessary sort nodes.
One solution to this problem would be to attach a filter to the result stream
of the table function. The filter would raise an exception if it encountered an
out-of-order tuple.
> Make it possible for table functions to declare that they return sorted
> results and make the optimizer exploit this information.
> --------------------------------------------------------------------------------------------------------------------------------
>
> Key: DERBY-6004
> URL: https://issues.apache.org/jira/browse/DERBY-6004
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 10.10.0.0
> Reporter: Rick Hillegas
>
> A derby-dev discussion has highlighted the need for table functions to return
> sorted results which the optimizer can exploit. See
> http://old.nabble.com/Have-Derby-Network-Server-having-an-out-of-memory-%28PermGen%29-to34704415.html#a34706722
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