Collections, Tuples, and User-defined Types - Learning Apache Cassandra - page 175

Defining collection columns
Given the limitations of the serialized approach, let's drop our text column and replace it
with a collection column of the same name. Cassandra offers three flavors of collec-
tions: lists, sets, and maps. We'll explore all three in this chapter, starting with a set column,
which is the most appropriate for our starred_by_users column:
ALTER TABLE "user_status_updates"
DROP "starred_by_users";
ALTER TABLE "user_status_updates"
ADD "starred_by_users" SET<text>;
The last line introduces a new syntax to define a collection column type. The new column
that we have created is a collection column using the SET data structure; the values it con-
tains have type text . Like normal scalar data columns, collection columns must define the
type of their values, and any type is permitted.
As the name suggests, set columns contain collections of values with the following proper-
ties:
• Values are not in a defined order
• Values are unique within the collection
This is just what we want for our starred_by_users column: a user can only star a
status update once, and we don't care about the order in which users starred an update.