Question

This article discusses possible ways CQL 3 could be used for creating composite columns in Cassandra 1.1. They are just ideas. Nothing is official, and the Datastax documentation doesn’t cover this (only composite keys).

As I understand it, composite columns are a number of columns that together have only one value.

How do you create them with CQL?

EDIT

I will be using C# to interface into Cassandra. CQL looks straightforward to use, which is why I want to use it.

Answer 1

You’ve got a couple concepts confused, I think. Quite possibly this is the fault of the Datastax documentation; if you have any good suggestions for making it clearer after you have a better picture, I’ll be glad to send them on.

The “composite keys” stuff in the Datastax docs is actually talking about composite Cassandra columns. The reason for the confusion is that rows in CQL 3 do not map directly to storage engine rows (what you work with when you use the thrift interface). “Composite key” in the context of a CQL table just means a primary key which consists of multiple columns, which is implemented by composite columns at the storage layer.

This article is one of the better explanations as to how the mapping happens and why the CQL model is generally easier to think about.

With this sort of use, the first CQL column becomes being the storage engine partition key.

As of Cassandra 1.2 (in development), it’s also possible to create composite storage engine keys using CQL, by putting extra parentheses in the PRIMARY KEY definition around the CQL columns that will be stored in the partition key (see CASSANDRA-4179), but that’s probably going to be the exception, not the rule.