每月的累计值总和，填写缺少的月份

Question

我有此数据表，我想知道是否有可能创建一个查询，以考虑 到当前月份的所有月份 按月累积的总和。

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

我需要这样的结果：

Jan|0
Feb|0
Mar|0
Apr|5
May|7
Jun|7
Jul|9
Aug|15

Answer 1

这与其他问题非常相似，但是最佳查询仍然很棘手。

基本查询 以快速获取运行总和：

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);

棘手的部分是 填写缺少的月份 ：

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;

该隐含CROSS JOINLATERAL需要的Postgres 9.3+。从表中的第一个月开始。
要 开始一个特定的月份 ：

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;

SQL提琴。

将不同年份的月份间隔数月。您并没有要求，但是您很可能会想要它。