Running/cumulative count using windows

From: Oliver Kohll - Mailing Lists <oliver(dot)lists(at)gtwm(dot)co(dot)uk>
To: pgsql-general(at)postgresql(dot)org
Subject: Running/cumulative count using windows
Date: 2010-03-30 11:06:16
Message-ID: DF46540C-2F08-40F0-BD8D-492E7C1461C2@gtwm.co.uk
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-general

Hello,

I'm still reasonably new to windowing functions, having used a few since 8.4 came out. I wonder if anyone can help with this one.

I've got a table of email addresses in a CRM system similar to the following:

CREATE TABLE test(
signup_date timestamp,
email_address varchar(1000)
);
INSERT INTO test(signup_date, email_address) VALUES(now(), 'test(at)test(dot)com');
INSERT INTO test(signup_date, email_address) VALUES(now(), 'test(at)test1(dot)com');
INSERT INTO test(signup_date, email_address) VALUES(now() - '1 month'::interval, 'test(at)test2(dot)com');

I'd like a running count, or cumulative count of the number of signups per month. I'm pretty sure a window function would do it but I can't work it out.

So a plain count by month would be

SELECT date_part('year',signup_date) as year, date_part('month',signup_date) as month, count(*)
FROM test
GROUP BY year, month
ORDER BY year, month;

giving

year | month | count
------+-------+-------
2010 | 2 | 1
2010 | 3 | 2

How would you make the count a cumulative one? The output should then be

year | month | count
------+-------+-------
2010 | 2 | 1
2010 | 3 | 3

Regards
Oliver Kohll

oliver(at)agilebase(dot)co(dot)uk / +44(0)845 456 1810 / skype:okohll
www.agilebase.co.uk - software
www.gtwm.co.uk - company

Responses

Browse pgsql-general by date

  From Date Subject
Next Message A. Kretschmer 2010-03-30 11:26:29 Re: Running/cumulative count using windows
Previous Message dipti shah 2010-03-30 11:05:27 Get the list of permissions on schema for current user