The explanation for Composite columns is muddied by verbage depending on
whether you are talking about the thrift interface which tends to talk
about things in low terms, or cql which tends to talk about things in
higher level terms.
At a thrift/low level, a composite column, really now called a composite
cell, is just a cell that has a name which contains multiple parts
packed into a ByteBuffer. These multiple parts are understood by
cassandra for validation, sorting and slicing purposes.
At a CQL level, there are really just compound keys, where the first
part of a compound key is the partition key, it alone decides where the
data lives (what node). The rest of the keys are clustering keys, and
effect cql row sorting.
In CQL, then, columns that exist after columns which are part of the
clustering keys, are grouped by those clustering keys. Under the cover
these extra columns have names that are prefixed by the
multipart-clustering name.
As for using column names as data, again it depends on the interface
thrift/cql as to how to look at it. For instance with thrift you can
slice columns that start from some value and end with some value, and
find column names between. What shows up as columns probably means
something to you.
HTH,
dave
On 10/17/2013 07:51 PM, Hartzman, Leslie wrote:
Hi,
I'm looking for clarification on composite keys and composite columns.
From what I've read with regards to composite keys, you have a
collection of columns where of 'n' columns, the first n-1 form the
composite primary key and the last column is the data for that
composite key. Do I have this right?
What I've just read about composite columns is that there are static
and dynamic composite column names, but dynamic should be avoided. If
the column names can be created programmatically, what does the schema
definition look like for this, or is it omitted since they're
programmatically created? I'm assuming that these are the dynamic
composite columns. So how are the static composite columns defined in
the schema?
Also, if a column name is used as the value as well (composite or
non-composite columns), how do you query that? If the value is empty
and the column name IS the value, is the knowledge of what you're
querying in the business logic due to the construct of that particular
column family?
Thanks.
Les
[CONFIDENTIALITY AND PRIVACY NOTICE] Information transmitted by this
email is proprietary to Medtronic and is intended for use only by the
individual or entity to which it is addressed, and may contain
information that is private, privileged, confidential or exempt from
disclosure under applicable law. If you are not the intended recipient
or it appears that this mail has been forwarded to you without proper
authority, you are notified that any use or dissemination of this
information in any manner is strictly prohibited. In such cases,
please delete this mail from your records. To view this notice in
other languages you can either select the following link or manually
copy and paste the link into the address bar of a web browser:
http://emaildisclaimer.medtronic.com
