[ 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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