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https://issues.apache.org/jira/browse/DERBY-886?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mamta A. Satoor updated DERBY-886:
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Urgency: Low
Labels: derby_triage10_11 (was: )
> allow system to use 2 different access paths for 2 different columns in a
> select list.
> --------------------------------------------------------------------------------------
>
> Key: DERBY-886
> URL: https://issues.apache.org/jira/browse/DERBY-886
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Reporter: Mike Matrigali
> Priority: Minor
> Labels: derby_triage10_11
>
> "SELECT MIN(Id) FROM Customer" and "SELECT MAX(Id) FROM Customer" are both
> fast, but "SELECT MIN(Id), MAX(Id) FROM Customer" is slow, taking 5 seconds.
> Derby knows how to use an index to quickly find a minimum or a maximum (by
> traversing down one side of the B-tree or the other). It doesn't know how to
> do both in the same query, which would take two traversals. There may be a
> few other cases in Derby where special access paths are used to return
> function results (I think there is some magic for finding if a null exists,
> but not sure).
> Some notes from discussion on the development list:
> >
> > Is the work to fix this the same as making IN list use multiple probes,
> > and/or makeing OR lists do multiple probes? There are existing JIRA
> > items for those, or is it different enough to have a separate JIRA?
> I believe they're different. While each case would use multiple probes, in
> the MIN/MAX case one of the probes would go down the right side of the BTree,
> while in the IN/OR case it would do "normal" scans. Also, the MIN/MAX case
> and the IN/OR case would require different logic to recognize when the
> optimizations are possible. The costing logic in the optimizer would be
> different, too. It's possible the two cases could share some execution code,
> but the rest of it would require different implementations.
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