[jira] [Commented] (CASSANDRA-18060) Add aggregation scalar functions on collections

["Benedict Elliott Smith (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-18060?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17642544#comment-17642544 ] 

Benedict Elliott Smith commented on CASSANDRA-18060:
----------------------------------------------------

Did you reject using the same function names as their simple aggregation variants for implementation reasons, or for semantic reasons?

> Add aggregation scalar functions on collections
> -----------------------------------------------
>
>                 Key: CASSANDRA-18060
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-18060
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: CQL/Semantics
>            Reporter: Andres de la Peña
>            Assignee: Andres de la Peña
>            Priority: Normal
>             Fix For: 4.2
>
>          Time Spent: 1h 40m
>  Remaining Estimate: 0h
>
> The new mechanism for dynamically building native functions introduced by CASSANDRA-17811 can be used to provide within-collection aggregation functions. We can use that mechanism to add new CQL functions to get:
>  * The number of items in a collection.
>  * The max/min items of a collection.
>  * The sum/avg of the items of a numeric collection.
>  * The keys or the values of a map.
> For example:
> {code:java}
> CREATE TABLE k.t (k int PRIMARY KEY, l list<int>, m map<int, int>);
> INSERT INTO t(k, l, m) VALUES (0, [1, 2, 3], {1:10, 2:20, 3:30});
> > SELECT map_keys(m), map_values(m) FROM t;
>  system.map_keys(m) | system.map_values(m)
> --------------------+----------------------
>           {1, 2, 3} |         [10, 20, 30]
> > SELECT collection_count(m), collection_count(l) FROM t;
>  system.collection_count(m) | system.collection_count(l)
> ----------------------------+----------------------------
>                           3 |                          3
> > SELECT collection_min(l), collection_max(l) FROM t;
>  system.collection_min(l) | system.collection_max(l)
> --------------------------+--------------------------
>                         1 |                        3
> > SELECT collection_sum(l), collection_avg(l) FROM t;
>  system.collection_sum(l) | system.collection_avg(l)
> --------------------------+--------------------------
>                         6 |                        2
> {code}
> Note that this type of aggregation is different from the kind of aggregation provided by {{min}}, {{max}}, {{sum}} and {{avg}}, which aggregate entire collections across rows. Here we only aggregate the items of a collection row per row.



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