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From "Kathey Marsden (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-681) Eliminate the parser's rewriting of the abstract syntax tree for queries with GROUP BY and/or HAVING clauses
Date Tue, 19 May 2009 00:24:45 GMT

    [ https://issues.apache.org/jira/browse/DERBY-681?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12710557#action_12710557
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Kathey Marsden commented on DERBY-681:
--------------------------------------

DERBY-4230 is a regression related to this issue.  If the links are correct, this is our 12th
regression related to this issue. The reports have trickled in over the past two years and
have had a wide variety of symptoms.

I wonder if anyone has any ideas for a testing plan that we might be able to use to pop any
additional issues related to this change? 

> Eliminate the parser's rewriting of the abstract syntax tree for queries with GROUP BY
and/or HAVING clauses
> ------------------------------------------------------------------------------------------------------------
>
>                 Key: DERBY-681
>                 URL: https://issues.apache.org/jira/browse/DERBY-681
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>            Reporter: Rick Hillegas
>            Assignee: Manish Khettry
>             Fix For: 10.3.1.4
>
>         Attachments: 681.patch.txt, 681.patch2.txt, 681.patch3.txt, followup.patch.txt,
notes.txt
>
>
> If a query contains a GROUP BY or HAVING clause, the parser rewrites the abstract syntax
tree, putting aggregates into a subselect and treating the HAVING clause as the WHERE clause
of a fabricated outer select from the subquery. This allows the compiler to re-use some machinery
since the HAVING clause operates on the grouped result the way that the WHERE clause operates
on the from list. Unfortunately, this rewriting creates an explosion of special cases in the
compiler after parsing is done. The rewriting is not systematically handled later on in the
compiler. This gives rise to defects like bug 280. We need to eliminate this special rewriting
and handle the HAVING clause in a straightforward way. This is not a small bugfix but is a
medium sized project.

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