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https://issues.apache.org/jira/browse/CASSANDRA-18085?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17643874#comment-17643874
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Andres de la Peña commented on CASSANDRA-18085:
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Just started a thread on the mail list:
[https://lists.apache.org/thread/nkm04oo9m60o7dcjzyrll7rzdqzzo1gy]
> Add support for singletons on CQL collection functions
> ------------------------------------------------------
>
> Key: CASSANDRA-18085
> URL: https://issues.apache.org/jira/browse/CASSANDRA-18085
> Project: Cassandra
> Issue Type: Improvement
> Components: CQL/Semantics
> Reporter: Andres de la Peña
> Assignee: Andres de la Peña
> Priority: Normal
> Fix For: 4.x
>
> Time Spent: 50m
> Remaining Estimate: 0h
>
> CASSANDRA-18060 has added generic CQL functions to get the min, max, sum, avg
> and number of items in a collection. These functions can only be applied to
> collection values. The functions throw an {{InvalidRequestEception}} when
> applied to not-collection values.
> CASSANDRA-18078 has been pointed out that those functions could be applied
> also to not-collection values, considering that the not-collection argument
> can be considered a collection of a single element. For example:
> * collection_min(7) = collection_min([7]) = collection_min(\{7}) = 7
> * collection_max(7) = collection_max([7]) = collection_max(\{7}) = 7
> * collection_sum(7) = collection_sum([7]) = collection_sum(\{7}) = 7
> * collection_avg(7) = collection_avg([7]) = collection_avg(\{7}) = 7
> * collection_count(7) = collection_count([7]) = collection_count(\{7}) = 1
> This would be particularly useful when used in combination with functions
> such as {{writetime}} and {{{}ttl{}}}. Those functions can return either
> single values or collections of values depending on whether the column passed
> as argument is multicell. Thus, users interested on getting the
> min/max/sum/avg of the writetimes/ttls of a column need to consider the type
> of the column when choosing what functions they should use. With the proposed
> change they could just use, for example,
> {{collection_max(writetime(column))}} regardless of the column type.
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