Let's say, I have events and users. I want to group events by properties of
users. In SQL it looks like this:
SELECT u.gender,
u.age,
u.nfr,
u.nafr,
e.event_id,
COUNT(e.id) ecount,
SUM(e.event_value) esum
FROM sn_users u
JOIN daily_events e on e.sn_user_id = u.sn_id
GROUP BY u.gender, u.age, u.nfr, u.nafr, e.event_id;
I understand that link walking with mapreduce may help me with this.
However, all examples of link walking I've seen so far substitute the
original document. That is, if I were to link-walk event document I'd get a
bunch of users, without events.
How it ideally should be (in my imagination).
- Links are walked on event documents and corresponding users are embedded
into events.
- Map function now acts on a "joined" document and can emit appropriate
values.
- Reduce - nothing fancy here.
Is it possible at all?
--
Best regards,
Sergei Tulentsev
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