Hi all,
I trying to run a query where, after doing a UNION on two different
SELECTs, I need to sort the result by username and log_date fields, and
then grab the last entry for each username ('last' as determined by the
ordering of the log_date field, which is a datetime).
GROUP BY seems like an obvious choice; 'GROUP BY username', to be
exact. However, this seems to produce not the last row's values, but
ones from a random row in the group.
I don't think the fact that I am doing this on a subquery is relevant,
but just in case, I am including this info.
Here is what the query looks like, abridged:
SELECT id,username,log_date,event_type
FROM (SELECT * FROM a
UNION
SELECT * from b) as h
GROUP BY username
Basically, what I need is the chronologically last event_type value for
each user. I can achieve something similar by doing SELECT
MAX(event_type) -- but I need the equivalent of SELECT LAST(event_type);
last row instead of max-field-value row.
I keep having a feeling that I am making this way more complicated than
it has to be, and that there's a very simple way to return only the last
row for each username; but i am at a loss as to how to do it.
--
Victor Danilchenko
Senior Software Engineer, AskOnline.net
[EMAIL PROTECTED] - 617-273-0119
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