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https://issues.apache.org/jira/browse/DERBY-2998?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12528705
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Thomas Nielsen commented on DERBY-2998:
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You have a valid point Knut.
Further investigation shows that the inner row_number() is executed once for
every outer execution - which is the way one would like to do this. The
following output from a test table with 3 rows illustrate this. Never mind the
bug not distinguishing between the two row_number()s for now, but it clearly
shows the order in which this is executed:
ij> select row_number(),r,a,b from (select row_number() as r, t.* from t) as tr
where r <=3;
row_number() |R |A |B
-----------------------------------------------------------------
2 |1 |1 |9
4 |3 |2 |8
2 rows selected
If the inner resultset was flagged as ordered on R the outer might use that
info to determine when to stop.
> 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-2.diff, row_number_prototype-2.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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