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From "Jonathan Ellis (Commented) (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-2474) CQL support for compound columns
Date Wed, 28 Dec 2011 19:00:31 GMT


Jonathan Ellis commented on CASSANDRA-2474:

The more I think about it the less happy I am with omitting support for sparse columns.  Remember
that dense composites may only be inserted and deleted, not updated, since they are just a
tuple of values with "column names" determined by schema and/or convention.

I think we can support sparse columns well in a way that improves the conceptual integrity
for the dense composites as well:

-- "column" and "value" are sparse; a transposed row will be stored as
-- two columns of (user_id, posted_at, 'column': string) and (user_id, posted_at, 'value':
CREATE TABLE timeline (
    user_id int,
    posted_at uuid,
    column string,
    value blob,    
    PRIMARY KEY(user_id, posted_at)

-- entire transposed row is stored as a single dense composite column
-- (series, ts1, cat, subcat, 1337, 92d21d0a-...: []).  Note that the
-- composite column's value is unused in this case.
    series text,
    ts1 int,
    cat text,
    subcat text,
    "1337" uuid,
    "92d21d0a-d6cb-437c-9d3f-b67aa733a19f" bigint,
    PRIMARY KEY(series, ts1, cat, subcat, "1337", "92d21d0a-d6cb-437c-9d3f-b67aa733a19f")
) TRANSPOSED WITH COLUMN NAMES ("1337" int, "92d21d0a-d6cb-437c-9d3f-b67aa733a19f" uuid);

Thus, columns included in the (transposed) primary key will be "dense," and not updateable,
which conforms to our existing practice that keys are not updateable.  Remaining columns will
be updateable since they will each map to a separate physical column.
> CQL support for compound columns
> --------------------------------
>                 Key: CASSANDRA-2474
>                 URL:
>             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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