Looking up rows by partition

The core reading experience of the MyStatus application will be an interface to read a given user's status updates. In order to do this, we need to be able to retrieve status updates for a given user from the user_status_updates table. As you might expect, this follows naturally from the CQL syntax we've seen in previous chapters:

SELECT * FROM "user_status_updates"
WHERE "username" = 'alice';

Previously, we've used the WHERE keyword to specify an exact value for a full primary key. In the preceding query, we only specify the partition key part of the primary key, which allows us to retrieve only those rows that we've asked for the partition:

In the results, we only see the rows whose username is alice. To emphasize what we discussed in the previous chapter, in the Looking up a specific status update section, this is a very efficient query. Cassandra stores all of alice's status updates together, already in order; so returning this view of the table is quite inexpensive.