Establishing Relationships - Learning Apache Cassandra - page 105

Unfollowing users
It's conceivable that bob may end up posting too many funny cat pictures for alice 's
taste, in which case, she may decide to unfollow him. For alice to do that, we'll need to
remove the rows representing the follow relationship from both the inbound and outbound
follow tables:
DELETE FROM "user_outbound_follows"
WHERE "follower_username" = 'alice'
AND "followed_username" = 'bob';
DELETE FROM "user_inbound_follows"
WHERE "followed_username" = 'bob'
AND "follower_username" = 'alice';
This is our first encounter with CQL's DELETE statement, although it should look quite fa-
miliar to anyone who's worked with SQL. To delete a row, we specify the full primary key
of the row, which is to say both the partition key(s) and the clustering column(s). The
WHERE…AND syntax is the same as that used in SELECT queries, introduced in Chapter 3 ,
Organizing Related Data .
To check the effects of the deletion, we can query again for the list of users alice fol-
lows:
SELECT "followed_username"
FROM "user_outbound_follows"
WHERE "follower_username" = 'alice';
As expected, alice no longer follows bob :
Were we to check the user_inbound_follows table for bob , we would find that he
no longer has any followers.