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From "Daniel John Debrunner (JIRA)" <derby-...@db.apache.org>
Subject [jira] Updated: (DERBY-681) Eliminate the parser's rewriting of the abstract syntax tree for queries with GROUP BY and/or HAVING clauses
Date Thu, 03 Nov 2005 21:10:59 GMT
     [ http://issues.apache.org/jira/browse/DERBY-681?page=all ]

Daniel John Debrunner updated DERBY-681:
----------------------------------------

    type: Improvement  (was: Bug)

Seems more like an improvement than a bug fix.

> Eliminate the parser's rewriting of the abstract syntax tree for queries with GROUP BY
and/or HAVING clauses
> ------------------------------------------------------------------------------------------------------------
>
>          Key: DERBY-681
>          URL: http://issues.apache.org/jira/browse/DERBY-681
>      Project: Derby
>         Type: Improvement
>     Reporter: Rick Hillegas

>
> 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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