I have this data table and I'm wondering if is possible create a query that get a cumulative sum by month considering all months until the current month.
date_added | qty
------------------------------------
2015-08-04 22:28:24.633784-03 | 1
2015-05-20 20:22:29.458541-03 | 1
2015-04-08 14:16:09.844229-03 | 1
2015-04-07 23:10:42.325081-03 | 1
2015-07-06 18:50:30.164932-03 | 1
2015-08-22 15:01:54.03697-03 | 1
2015-08-06 18:25:07.57763-03 | 1
2015-04-07 23:12:20.850783-03 | 1
2015-07-23 17:45:29.456034-03 | 1
2015-04-28 20:12:48.110922-03 | 1
2015-04-28 13:26:04.770365-03 | 1
2015-05-19 13:30:08.186289-03 | 1
2015-08-06 18:26:46.448608-03 | 1
2015-08-27 16:43:06.561005-03 | 1
2015-08-07 12:15:29.242067-03 | 1
I need a result like that:
Jan|0
Feb|0
Mar|0
Apr|5
May|7
Jun|7
Jul|9
Aug|15
This is very similar to other questions, but the best query is still tricky.
Basic query to get the running sum quickly:
SELECT to_char(date_trunc('month', date_added), 'Mon YYYY') AS mon_text
, sum(sum(qty)) OVER (ORDER BY date_trunc('month', date_added)) AS running_sum
FROM tbl
GROUP BY date_trunc('month', date_added)
ORDER BY date_trunc('month', date_added);
The tricky part is to fill in for missing months:
WITH cte AS (
SELECT date_trunc('month', date_added) AS mon, sum(qty) AS mon_sum
FROM tbl
GROUP BY 1
)
SELECT to_char(mon, 'Mon YYYY') AS mon_text
, sum(c.mon_sum) OVER (ORDER BY mon) AS running_sum
FROM (SELECT min(mon) AS min_mon FROM cte) init
, generate_series(init.min_mon, now(), interval '1 month') mon
LEFT JOIN cte c USING (mon)
ORDER BY mon;
The implicit CROSS JOIN LATERAL
requires Postgres 9.3+. This starts with the first month in the table.
To start with a given month:
WITH cte AS (
SELECT date_trunc('month', date_added) AS mon, sum(qty) AS mon_sum
FROM tbl
GROUP BY 1
)
SELECT to_char(mon, 'Mon YYYY') AS mon_text
, COALESCE(sum(c.mon_sum) OVER (ORDER BY mon), 0) AS running_sum
FROM generate_series('2015-01-01'::date, now(), interval '1 month') mon
LEFT JOIN cte c USING (mon)
ORDER BY mon;
Keeping months from different years apart. You did not ask for that, but you'll most likely want it.
Note that the "month" to some degree depends on the time zone setting of the current session! Details:
Related: