From: | David G Johnston <david(dot)g(dot)johnston(at)gmail(dot)com> |
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To: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Not able to understand how to write group by |
Date: | 2014-07-02 19:18:23 |
Message-ID: | 1404328703594-5810279.post@n5.nabble.com |
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Lists: | pgsql-general |
afonit wrote
>> gender participants answer1_avg answer2_avg
>> n 3 12 3
>> m 5 4 12
>> f 7 15 23
Are you sure this is what you want?
Since there are two columns you will have to either use a CASE or a
sub-select to facilitate calculating the values for each of the columns.
SELECT gender, answer1_avg, answer2_avg
FROM (SELECT DISTINCT gender FROM ...) gn
LEFT JOIN (SELECT gender, answer1_avg FROM ...) ans1 USING (gender)
LEFT JOIN (SELECT gender, answer2_avg FROM ...) ans2 USING (gender)
You could also try learning "crosstab" from the "tablefunc" extension:
http://www.postgresql.org/docs/9.3/interactive/tablefunc.html
I do not see how a single "participant count" column will provide a
meaningful piece of data...
David J.
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