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Sylvain Lebresne commented on CASSANDRA-4914:
---------------------------------------------
The last patch looks almost good to go (provided it's rebased) for me but there
seems to be some confusion around the {{reset}} method for {{Selection}}.
You've removed the abstract one in {{Selection}} itself, but both
{{SimpleSelection}} and {{SelectionWithFunctions}} still have a {{reset}}
method which, as far as I can tell, is never called. And while the one in
{{SimpleSelection}} does nothing, the one in {{SelectionWithFunctions}} seems
to do something. I think what you'd want is add back the {{reset}} method to
{{Selection}} but actually call it in {{ResultSetBuilder.newRow/build}} (as a
nit, you can then move the {{current = null}} in {{SimpleSelection}} in the
{{reset}} method for consistency).
bq. Postgres's approach to user-defined aggregation functions is almost
exactly this: http://www.postgresql.org/docs/8.3/static/sql-createaggregate.html
I agree that it's where we want to go (there was some discussion around this at
the bootcamp that ended up with the same conclusion but it sound like I forgot
to update JIRA with said conclusions). That said, this ticket is mostly about
the internal interface for aggregation functions and as far as I can tell,
nothing in the attached patch limit us from going with a "reduce-style"
approach for UDF (it will be in fact rather simple). So let's maybe leave the
discussion on UDF in CASSANDRA-8053.
> Aggregation functions in CQL
> ----------------------------
>
> Key: CASSANDRA-4914
> URL: https://issues.apache.org/jira/browse/CASSANDRA-4914
> Project: Cassandra
> Issue Type: New Feature
> Reporter: Vijay
> Assignee: Benjamin Lerer
> Labels: cql, docs
> Fix For: 3.0
>
> Attachments: CASSANDRA-4914-V2.txt, CASSANDRA-4914-V3.txt,
> CASSANDRA-4914-V4.txt, CASSANDRA-4914.txt
>
>
> The requirement is to do aggregation of data in Cassandra (Wide row of column
> values of int, double, float etc).
> With some basic agree gate functions like AVG, SUM, Mean, Min, Max, etc (for
> the columns within a row).
> Example:
> SELECT * FROM emp WHERE empID IN (130) ORDER BY deptID DESC;
>
> empid | deptid | first_name | last_name | salary
> -------+--------+------------+-----------+--------
> 130 | 3 | joe | doe | 10.1
> 130 | 2 | joe | doe | 100
> 130 | 1 | joe | doe | 1e+03
>
> SELECT sum(salary), empid FROM emp WHERE empID IN (130);
>
> sum(salary) | empid
> -------------+--------
> 1110.1 | 130
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