Re: cumulative count

2008/12/4 Carson Farmer <carson(dot)farmer(at)gmail(dot)com>:
> Hi list,
>
> This is my first post to pgsql, so hopefully I'm not asking something that
> has been answered a thousand time before. I've looked online, and through
> the archives, but I haven't found anything that answers my question
> specifically:
>
> Say I have a table like this:
>
> date | user
> ------------------+---------------------
> 20050201 | Bill
> 20050210 | Steve
> 20050224 | Sally
> 20050311 | Martha
> 20050316 | Ryan
> 20050322 | Phil
> 20050330 | William
> 20050415 | Mary
> 20050428 | Susan
> 20050503 | Jim
>
> and I want to run a query that returns a *count* of the number of users
> *each month*, ordered by year and *month*, with an additional column that is
> a *running total of the count*, as in:
>
> year | month | count | run_count
> -------------------+----------------+----------------+-----------------
> 2005 | 02 | 3 | 3 2005
> | 03 | 4 | 7
> 2005 | 04 | 2 | 9
> 2005 | 05 | 1 | 10
>
> I can get almost everything I want with:
>
> SELECT a.year, a.month, a.count, a.month_name, sum(b.count) AS total
> FROM (SELECT EXTRACT(year from added_date) AS year,
> EXTRACT(month FROM added_date) AS month,
> TO_CHAR(added_date, 'Month') AS month_name,
> COUNT(*) AS count FROM users_table GROUP BY 1, 2, 3) AS a,
> (SELECT EXTRACT(year FROM added_date) AS year,
> EXTRACT(month FROM added_date) AS month,
> TO_CHAR(added_date, 'Month') AS month_name,
> COUNT(*) AS count
> FROM users_table GROUP BY 1, 2, 3) AS b
> WHERE a.year >= b.year AND a.month >= b.month
> GROUP BY 1, 2, 3, 4
> ORDER BY a.year, a.month asc;
>
> but I can't quite figure out the running total of the count. The above
> example works right up to the end of the first year, then the values no
> longer make sense. My guess is it's something to do with my WHERE clause,
> but I can't think of a better way to do things.
>
> Any ideas?
>

hate selfjoins. It is really slow for any bigger datasets. Write SRF
function (stored function that returns table).

Regards
Pavel Stehule

> Cheers,
>
> Carson
>
>
>
>
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