cassandra composite index and compact storages - cassandra

Question

I am new in cassandra, have not run it yet, but my business logic requires to create such table.
CREATE TABLE Index(
user_id uuid,
keyword text,
score text,
fID int,
PRIMARY KEY (user_id, keyword, score); )
WITH CLUSTERING ORDER BY (score DESC) and COMPACT STORAGE;
Is it possible or not? I have only one column(fID) which is not part of my composite index, so i hope I will be able to apply compact_storage setting. Pay attention thet I ordered by third column of my composite index, not second. I need to compact the storage as well, so the keywords will not be repeated for each fID.

Answer 1

A few things initially about your CREATE TABLE statement:
It will error on the semicolon (;) after your PRIMARY KEY definition.
You will need to pick a new name, as Index is a reserved word.
Pay attention thet I ordered by third column of my composite index, not second.
You cannot skip a clustering key when you specify CLUSTERING ORDER.
However, I do see an option here. Depending on your query requirements, you could simply re-order keyword and score in your PRIMARY KEY definition, and then it would work:
CREATE TABLE giveMeABetterName(
user_id uuid,
keyword text,
score text,
fID int,
PRIMARY KEY (user_id, score, keyword)
) WITH CLUSTERING ORDER BY (score DESC) and COMPACT STORAGE;
That way, you could query by user_id and your rows (keywords?) for that user would be ordered by score:
SELECT * FROM giveMeABetterName WHERE `user_id`=1b325b66-8ae5-4a2e-a33d-ee9b5ad464b4;
If that won't work for your business logic, then you might have to retouch your data model. But it is not possible to skip a clustering key when specifying CLUSTERING ORDER.
Edit
But re-ordering of columns does not work for me. Can I do something like this WITH CLUSTERING ORDER BY (keyword asc, score desc)
Let's look at some options here. I created a table with your original PRIMARY KEY, but with this CLUSTERING ORDER. That will technically work, but look at how it treats my sample data (video game keywords):
aploetz#cqlsh:stackoverflow> SELECT * FROM givemeabettername WHERE user_id=dbeddd12-40c9-4f84-8c41-162dfb93a69f;
user_id | keyword | score | fid
--------------------------------------+------------------+-------+-----
dbeddd12-40c9-4f84-8c41-162dfb93a69f | Assassin's creed | 87 | 0
dbeddd12-40c9-4f84-8c41-162dfb93a69f | Battlefield 4 | 9 | 0
dbeddd12-40c9-4f84-8c41-162dfb93a69f | Uncharted 2 | 91 | 0
(3 rows)
On the other hand, if I alter the PRIMARY KEY to cluster on score first (and adjust CLUSTERING ORDER accordingly), the same query returns this:
user_id | score | keyword | fid
--------------------------------------+-------+------------------+-----
dbeddd12-40c9-4f84-8c41-162dfb93a69f | 91 | Uncharted 2 | 0
dbeddd12-40c9-4f84-8c41-162dfb93a69f | 87 | Assassin's creed | 0
dbeddd12-40c9-4f84-8c41-162dfb93a69f | 9 | Battlefield 4 | 0
Note that you'll want to change the data type of score from TEXT to a numeric (int/bigint) to avoid ASCII-betical sorting, like this:
user_id | score | keyword | fid
--------------------------------------+-------+------------------+-----
dbeddd12-40c9-4f84-8c41-162dfb93a69f | 91 | Uncharted 2 | 0
dbeddd12-40c9-4f84-8c41-162dfb93a69f | 9 | Battlefield 4 | 0
dbeddd12-40c9-4f84-8c41-162dfb93a69f | 87 | Assassin's creed | 0
Something that might help you, is to read through this DataStax doc on Compound Keys and Clustering.