The First Table - Learning Apache Cassandra - page 37

Partial inserts
You are not, of course, required to provide values for all columns—other than primary key
columns—when inserting a row. If, for instance, we decide to allow users to register
without providing an email, we may issue this perfectly valid query:
INSERT INTO "users"
("username", "encrypted_password")
VALUES (
'bob',
0x10920941a69549d33aaee6116ed1f47e19b8e713
);
In the above query, we only insert values for the username and encryp-
ted_password fields; the row will have no value in the email field.
Note
Do empty columns take up space?
Only columns with values take up storage space in Cassandra. This is in contrast to rela-
tional databases in which every row has space allocated for every column, whether or not
that column has a value. So, there's little downside to defining columns in Cassandra that
you expect to rarely populate; they'll only take up space where they have values.
For a full reference on the INSERT statement in CQL, consult the DataStax CQL docu-
mentation at http://www.datastax.com/documentation/cql/3.1/cql/cql_reference/in-
sert_r.html . We haven't explored all of the possibilities for INSERT statements yet, but
we'll cover many of them in future chapters.