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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3002) Add support for GROUP BY ROLLUP
Date Fri, 29 May 2009 18:26:45 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3002?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12714542#action_12714542
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Knut Anders Hatlen commented on DERBY-3002:
-------------------------------------------

I think the results in your examples without rollup are correct. At least I see the same same
results when I try the statements in PostgreSQL. When you have GROUP BY and no rows in the
table, there are no groups, so the result should be empty.

The wiki page says that a rollup query is semantically equivalent to a union where the last
subquery in the union has no group by. I think this means that this query

  SELECT a, count(*) FROM T GROUP BY ROLLUP(a)

should be equivalent to

  SELECT a, COUNT(*) FROM T GROUP BY (a)
    UNION
  SELECT NULL, COUNT(*) FROM T

Since SELECT NULL, COUNT(*) FROM T always returns one row, the union query should always return
at least one row.

> 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, prototypeChangeNoTests.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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