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https://issues.apache.org/jira/browse/CASSANDRA-7396?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16028127#comment-16028127
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Benjamin Lerer commented on CASSANDRA-7396:
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Forbidding these selectors is, in my opinion, different from what is done for
clustering keys and inequality predicates. Before to {{3.0}} we were preventing
any clustering restrictions after an inequality predicate, simply because we
had not put in place a mechanism to handle those queries. Since {{3.0}}, we
allow them as long as {{ALLOW FILTERING}} is specified.
CQL allow things like {{SELECT v + 1 - 1 FROM myTable}}, even if it is
inefficient. One of the problem of CQL is that it has a lot of corner cases,
that makes the language difficult to use and I have seen a lot of complains
about it. Which is why I am not in favor rejecting some specific mix of
selectors.
Moreover, you do not really want to forbid further operations after a slice as
a query like {{SELECT filterMap(m\[1..\])\[..2\] FROM ...}} can totally make
sense. And blocking a query like {{SELECT m\[1..\]\[..2\] FROM ...}} but not a
query like {{SELECT filterMap(m\[1..\])\[..2\] FROM ...}}, even if the
{{filterMap}} function is not doing any filtering, is also inconsistent.
So, from consistency point of view, I would argue that we should keep the
current behavior and not forbid further restrictions after a slice.
The operations perfomed by the selectors are straight forward:
* {{\[?\]}}: returns a collection element
* {{\[?..?\]}}: returns a slice of the collection
There is no notion of {{inner}} or {{outer}} collections because the selectors
can be used on a collection that does not contains another collection.
> Allow selecting Map key, List index
> -----------------------------------
>
> Key: CASSANDRA-7396
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7396
> Project: Cassandra
> Issue Type: New Feature
> Components: CQL
> Reporter: Jonathan Ellis
> Assignee: Sylvain Lebresne
> Labels: cql, docs-impacting
> Fix For: 4.x
>
> Attachments: 7396_unit_tests.txt
>
>
> Allow "SELECT map['key]" and "SELECT list[index]." (Selecting a UDT subfield
> is already supported.)
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