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https://issues.apache.org/jira/browse/DERBY-4331?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12738424#action_12738424
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Kathey Marsden commented on DERBY-4331:
---------------------------------------
One thing I don't understand about this regression is the description of the
fix for DERBY-3926 made it sound like it was making sort avoidance less likely.
" The decision for avoiding sorting should also include relationship between
the optimizables in a given join order "
so how did that cause a new sort avoidance problem?
The comments also say:
"I think this patch is also improving the existing queries to include a better
path than what it was picking up before."
Is it a change in plan that is causing the regression, perhaps choosing a plan
that had always ordered incorrectly?
> Join returns results in wrong order
> -----------------------------------
>
> Key: DERBY-4331
> URL: https://issues.apache.org/jira/browse/DERBY-4331
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.1.3.3, 10.2.2.1, 10.3.3.1, 10.4.2.1, 10.5.2.0,
> 10.6.0.0
> Reporter: Knut Anders Hatlen
> Attachments: repro.sql
>
>
> In Derby 10.5.2.0, the query below started returning results in wrong order
> (note the ORDER BY clause). Derby 10.5.1.1 gives the expected ordering.
> ij> SELECT CS.ID
> FROM
> CHANGESETS CS, FILECHANGES FC, REPOSITORIES R, FILES F, AUTHORS A
> WHERE
> R.PATH = '/var/tmp/source5923202038296723704opengrok/mercurial' AND
> F.REPOSITORY = R.ID AND A.REPOSITORY = R.ID AND
> CS.REPOSITORY = R.ID AND CS.ID = FC.CHANGESET AND F.ID = FC.FILE AND
> A.ID = CS.AUTHOR AND
> EXISTS (
> SELECT 1
> FROM FILES F2
> WHERE
> F2.ID = FC.FILE AND F2.REPOSITORY = R.ID AND
> F2.PATH LIKE '/%' ESCAPE '#')
> ORDER BY CS.ID DESC;
> ID
> -----------
> 1
> 2
> 3
> 2
> 2
> 3
> 6 rows selected
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