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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3002) Add support for GROUP BY ROLLUP
Date Tue, 23 Jun 2009 14:41:07 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3002?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12723093#action_12723093
] 

Knut Anders Hatlen commented on DERBY-3002:
-------------------------------------------

Hi Bryan,

Thanks for adding all the test cases. I haven't dived into the details of the latest patch,
but I have a couple of questions:

The patch changes how we compute aggregates for the non-rollup case as well, and a comment
in the patch says that the old technique was efficient. Have you planned to run tests to verify
that we don't introduce any performance regressions for non-rollup group bys?

Some of the run-time statistics for existing queries have changed, returning more rows from
the sorts. Is that expected?

What are the memory requirements for the in-memory hash table? Does it hold one copy of every
unique value in the table/query? Can it run out of memory if the query accesses a very large
table?

> Add support for GROUP BY ROLLUP
> -------------------------------
>
>                 Key: DERBY-3002
>                 URL: https://issues.apache.org/jira/browse/DERBY-3002
>             Project: Derby
>          Issue Type: New Feature
>          Components: SQL
>    Affects Versions: 10.4.1.3
>            Reporter: Bryan Pendleton
>            Assignee: Bryan Pendleton
>            Priority: Minor
>         Attachments: fixWhiteSpace.diff, IncludesASimpleTest.diff, passesRegressionTests.diff,
prototypeChangeNoTests.diff, rewriteGroupByRS.diff, rollupNullability.diff, useLookahead.diff
>
>
> Provide an implementation of the ROLLUP form of multi-dimensional grouping according
to the SQL standard.
> See http://wiki.apache.org/db-derby/OLAPRollupLists for some more detailed information
about this aspect of the SQL standard.

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