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https://issues.apache.org/jira/browse/CASSANDRA-2474?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13173487#comment-13173487
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Jonathan Ellis commented on CASSANDRA-2474:
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bq. you simply can't represent slices of wide, composite rows sanely that way
without something like transposition to expose the structure "hidden"
underneath.
Put another way: we've always said the "right" way to model is to have one
"atom" of data per CF -- that is, data that is queried together should go in
the same CF. But, we haven't enforced this in the API. From my perspective,
that's a bug, not a feature. If we *do* have a single type of data (or type of
record) per CF, then we can make relational-style resultsets out of it; the
only question is, how do we expose that in the query language. And the
conclusion I'm coming to is that we shouldn't have to change the language;
CQL-modeled-on-SQL is already good at describing sets of a given type of data.
So the right thing to do is to provide hints in the DDL that tell Cassandra how
to represent it at definition time, rather than at query time.
"Document" data doesn't change this, it's just an expansion of what we consider
a "record" or "atom". Should we be able to have wide rows of documents? Yes.
(E.g., by having a column type "json.") But I don't think we need to boil that
ocean here.
TLDR: I am totally fine with having some constructs technically representable
using composite columns, that we don't actually allow building from the API.
Total schema-freedom is not a design goal.
> CQL support for compound columns
> --------------------------------
>
> Key: CASSANDRA-2474
> URL: https://issues.apache.org/jira/browse/CASSANDRA-2474
> Project: Cassandra
> Issue Type: New Feature
> Components: API, Core
> Reporter: Eric Evans
> Assignee: Pavel Yaskevich
> Labels: cql
> Fix For: 1.1
>
> Attachments: 2474-transposed-1.PNG, 2474-transposed-raw.PNG,
> 2474-transposed-select-no-sparse.PNG, 2474-transposed-select.PNG,
> raw_composite.txt, screenshot-1.jpg, screenshot-2.jpg
>
>
> For the most part, this boils down to supporting the specification of
> compound column names (the CQL syntax is colon-delimted terms), and then
> teaching the decoders (drivers) to create structures from the results.
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