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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-2998) Add support for ROW_NUMBER() window function
Date Mon, 10 Sep 2007 19:17:29 GMT

    [ https://issues.apache.org/jira/browse/DERBY-2998?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12526227
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Bryan Pendleton commented on DERBY-2998:
----------------------------------------

Hi Thomas, thanks for posting the patch! I'll try to have a look at the code soon.

Perhaps we could treat the inability to reference the "AS R" renamed column in the WHERE clause
as a separate issue since, as you observe, it is a problem with all column expressions, not
just row_number() expressions. The most commonly-requested use of row_number() is probably
going to be for limiting the number of rows retried, as in DERBY-581.

If you use the nested select form, to limit the results:

  select * from (select row_number() as rownum, * from t) where runum <= 10

then does the execution logic actually short-circuit the evaluation properly after the first
10 rows have been read? Or does the execution of this query run through the entire table and
then later end up discarding all the rows beyond the first 10?

Since one of the primary goals of DERBY-581 is to efficiently limit the processing to only
a small subset of the rows, we want to make sure that we achieve that result if possible.


> Add support for ROW_NUMBER() window function
> --------------------------------------------
>
>                 Key: DERBY-2998
>                 URL: https://issues.apache.org/jira/browse/DERBY-2998
>             Project: Derby
>          Issue Type: Sub-task
>          Components: SQL
>            Reporter: Thomas Nielsen
>            Assignee: Thomas Nielsen
>            Priority: Minor
>         Attachments: row_number_prototype.diff, row_number_prototype.stat
>
>
> As part of implementing the overall OLAP Operations features of SQL (DERBY-581), implement
the ROW_NUMBER() window function.
> More information about this feature is available at http://wiki.apache.org/db-derby/OLAPRowNumber

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