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https://issues.apache.org/jira/browse/DERBY-2998?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12536670
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Thomas Nielsen commented on DERBY-2998:
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Here's how it seems to work for indexes for the following simple query on table
t where column a is the primary key.
select * from t where a <= 2;
During parsing we add a CursorNode and an IndexToBaseRowNode to the QueryTree
since we have an index on 'a'.
Based on the IndexToBaseRowNode we create the accompanying
IndexRowToBaseRowResultSet and feed any restrictions to its constructor.
In my case the restriction is generated code for '<='.
On opening the IndexRowToBaseRowResultSet we also call its "source" .openCore()
method BulkTableScanResultSet.openCore().
BulkTableScanResultSet does just that, it reads a base table or an index in
bulk (chunks) from Store.
The execution then does a do-while loop that calls .getNextRowCore(). For each
pass it invokes the restriction code it got its the constructor with
restriction.invoke(). In my case this ends up invoking
SQLInteger.lessOrEqual(). The do-while loop exits once the restriction is met.
The key seems to be the three calls to openCore(), getNextRowCore() and
closeCore(), and overrides of these in the ResultSet subclasses.
> 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-2c.diff,
> row_number_prototype-2c.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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