Suppose I had this table.
CREATE TABLE keyspace.user_event (
user_name varchar,
user_email varchar,
event_type int,
event_time timestamp,
a varchar,
b varchar,
c varchar
PRIMARY KEY ((user_name, user_email), event_type, event_time)
) WITH CLUSTERING ORDER BY (event_type ASC, event_time DESC);
I am interested in finding the most recent user_event for every unique event_type given a user_name an user_email and a subset of event_types. A composed query would look like this, as an example.
SELECT user_name,
user_email,
event_type,
max(event_time) AS event_time,
a,
b,
c
FROM user_event
WHERE user_name = 'user_name3'
AND user_email = 'user_email3'
AND event_type IN ( 301, 219, 206, 226 )
GROUP BY event_type;
Will this cassandra query behave the way I'd expect it to? If not, how might I reformulate the query? I want columns a, b, and c to match with the max row returned with the aggregate, max(event_time).
Now, as per https://docs.datastax.com/en/dse/5.1/cql/cql/cql_reference/cqlAggregates.html, cassandra will default to the first row of a non aggregate column. Because I specified the partition key in full, I am expecting a single partition to get searched, and therefore the ordering of the clustering keys to be consistent within that partition.
With local testing on a few rows, I haven't been able to break the query yet, but I want to ensure that I am not missing any unexpected behavior.
An an example, suppose we had the following data.
|user_email |user_name |event_type|a |b |c |event_time |
|-----------|-----------|----------|---|---|---|-------------------------|
|user_email2| user_name2|219 |a1 |b1 |c1 | 2019-10-01 18:50:25.653Z|
|user_email3| user_name3|219 |a2 |b2 |c2 | 2019-10-01 18:50:25.665Z|
|user_email3| user_name3|226 |a3 |b3 |c3 | 2019-10-01 21:37:05.663Z|
|user_email3| user_name3|301 |a4 |b4 |c4 | 2019-10-01 18:50:35.658Z|
|user_email3| user_name3|301 |a5 |b5 |c5 | 2019-10-01 18:50:25.660Z|
|user_email3| user_name3|301 |a6 |b6 |c6 | 2019-10-01 18:50:25.656Z|
|user_email1| user_name1|206 |a7 |b7 |c7 | 2019-10-01 18:50:25.604Z|
The expected output for the above query would be.
event_type | a,b,c |
-----------|------------|
226 | a3, b3, c3 |
219 | a2, b2, c2 |
301 | a4, b4, c4 |