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From "Robert Stupp (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9767) Allow the selection of columns together with aggregates
Date Thu, 16 Jul 2015 20:09:04 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9767?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14630242#comment-14630242
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Robert Stupp commented on CASSANDRA-9767:
-----------------------------------------

OK - then go ahead with the {{isSet}}. First row may make sense for C* - at least when aggregates
are used on a single column. I guess it would also be fine to document this behavior as intended
- as long as the aggregation query is restricted to a single partition; so the values are
taken from the first row in that partition according to the table definition/clustering key.

Out of curiosity, do you remember what the problem was?

Ah - forgot that: can you check {{CQL.textile}} and add some notes about the new behavior/possibilities
with aggregations and count?

> Allow the selection of columns together with aggregates
> -------------------------------------------------------
>
>                 Key: CASSANDRA-9767
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9767
>             Project: Cassandra
>          Issue Type: Wish
>          Components: Core
>         Environment: Cassandra 2.0.16
> Ubuntu 15.04
>            Reporter: Ajay
>            Assignee: Benjamin Lerer
>            Priority: Minor
>
> Lets assume we have a column family as below:
> create table sample ( track_id int, user_id int, country varchar, primary key ((track_id),
user_id));
> where track_id is the partition key.
> Now to aggregate the number of rows for a single track_id, we can query using CQL as
below:
> select count(*) where track_id = 1 and user_id = 1;
> But that will return only the count. If we need the other columns along with the count,
we cannot query as below as it throws error:
>  select count(*), country  from sample where track_id = 1 and user_id = 1;
> Bad Request: line 1:15 mismatched input ',' expecting K_FROM.
> In this case, all rows for a given track_id and user_id will have the same value for
country. So we should be able to query as above.  Also in SQL, it is possible to select columns
along with aggregate functions.
> Though I know that Cassandra is not analytics (unlike Hadoop and Spark), we need some
basic aggregate functions like min, max, avg etc....Though performance wise it might not be
efficient, but it is better done in the cassandra side (as it uses native protocol) than we
getting all rows in the client and doing the basic aggregation.  It cannot used just as a
data store (as garbage-in garbage-out). In that context, currently CQL is pretty limited.
Just for getting data out of cassandra, we will have to spark though we will not be doing
much analytics on it.



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