GROUP BY next months over N years - sql

Question

I need to aggregate amounts grouped by "horizon" 12 next months over 5 year:
assuming we are 2015-08-15
SUM amount from 0 to 12 next months (from 2015-08-16 to 2016-08-15)
SUM amount from 12 to 24 next months (from 2016-08-16 to 2017-08-15)
SUM amount from 24 to 36 next months ...
SUM amount from 36 to 48 next months
SUM amount from 48 to 60 next months
Here is a fiddled dataset example:
+----+------------+--------+
| id | date | amount |
+----+------------+--------+
| 1 | 2015-09-01 | 10 |
| 2 | 2015-10-01 | 10 |
| 3 | 2016-10-01 | 10 |
| 4 | 2017-06-01 | 10 |
| 5 | 2018-06-01 | 10 |
| 6 | 2019-05-01 | 10 |
| 7 | 2019-04-01 | 10 |
| 8 | 2020-04-01 | 10 |
+----+------------+--------+
Here is the expected result:
+---------+--------+
| horizon | amount |
+---------+--------+
| 1 | 20 |
| 2 | 20 |
| 3 | 10 |
| 4 | 20 |
| 5 | 10 |
+---------+--------+
How can I get these 12 next months grouped "horizons" ?
I tagged PostgreSQL but I'm actually using an ORM so it's just to find the idea. (by the way I don't have access to the date formatting functions)

Answer 1

I would split by 12 months time frame and group by this:
SELECT
FLOOR(
(EXTRACT(EPOCH FROM date) - EXTRACT(EPOCH FROM now()))
/ EXTRACT(EPOCH FROM INTERVAL '12 month')
) + 1 AS "horizon",
SUM(amount) AS "amount"
FROM dataset
GROUP BY horizon
ORDER BY horizon;
SQL Fiddle
Inspired by: Postgresql SQL GROUP BY time interval with arbitrary accuracy (down to milli seconds)

Answer 2

Assuming you need intervals from current date to this day next year and so on, I would query this like this:
SELECT 1 AS horizon, SUM(amount) FROM dataset
WHERE date > now()
AND date < (now() + '12 months'::INTERVAL)
UNION
SELECT 2 AS horizon, SUM(amount) FROM dataset
WHERE date > (now() + '12 months'::INTERVAL)
AND date < (now() + '24 months'::INTERVAL)
UNION
SELECT 3 AS horizon, SUM(amount) FROM dataset
WHERE date > (now() + '24 months'::INTERVAL)
AND date < (now() + '36 months'::INTERVAL)
UNION
SELECT 4 AS horizon, SUM(amount) FROM dataset
WHERE date > (now() + '36 months'::INTERVAL)
AND date < (now() + '48 months'::INTERVAL)
UNION
SELECT 5 AS horizon, SUM(amount) FROM dataset
WHERE date > (now() + '48 months'::INTERVAL)
AND date < (now() + '60 months'::INTERVAL)
ORDER BY horizon;
You can generalize it and make something like this using additional variable:
SELECT number AS horizon, SUM(amount) FROM dataset
WHERE date > (now() + ((number - 1) * '12 months'::INTERVAL))
AND date < (now() + (number * '12 months'::INTERVAL));
Where number is an integer from range [1,5]
Here is what I get from the Fiddle:
| horizon | sum |
|---------|-----|
| 1 | 20 |
| 2 | 20 |
| 3 | 10 |
| 4 | 20 |
| 5 | 10 |

Answer 3

Perhaps CTE?
WITH RECURSIVE grps AS
(
SELECT 1 AS Horizon, (date '2015-08-15') + interval '1' day AS FromDate, (date '2015-08-15') + interval '1' year AS ToDate
UNION ALL
SELECT Horizon + 1, ToDate + interval '1' day AS FromDate, ToDate + interval '1' year
FROM grps WHERE Horizon < 5
)
SELECT
Horizon,
(SELECT SUM(amount) FROM dataset WHERE date BETWEEN g.FromDate AND g.ToDate) AS SumOfAmount
FROM
grps g
SQL fiddle

Answer 4

Rather simply:
SELECT horizon, sum(amount) AS amount
FROM generate_series(1, 5) AS s(horizon)
JOIN dataset ON "date" >= current_date + (horizon - 1) * interval '1 year'
AND "date" < current_date + horizon * interval '1 year'
GROUP BY horizon
ORDER BY horizon;

Answer 5

You need a union and an aggregate function:
select 1 as horizon,
sum(amount) amount
from the_table
where date >= current_date
and date < current_date + interval '12' month
union all
select 2 as horizon,
sum(amount) amount
where date >= current_date + interval '12' month
and date < current_date + interval '24' month
union all
select 3 as horizon,
sum(amount) amount
where date >= current_date + interval '24' month
and date < current_date + interval '36' month
... and so on ...
But I don't know, how to do that with an obfuscation layer (aka ORM) but I'm sure it supports (or it should) aggregation and unions.
This could easily be wrapped up into a PL/PgSQL function where you pass the "horizon" and the SQL is built dynamically so that all you need to call is something like: select * from sum_horizon(5) where 5 indicates the number of years.
Btw: date is a horrible name for a column. For one because it's a reserved word, but more importantly because it doesn't document the meaning of the column. Is it a "release date"? A "due date"? An "order date"?

Answer 6

Try this
select
id,
sum(case when date>=current_date and date<current_date+interval 1 year then amount else 0 end) as year1,
sum(case when date>=current_date+interval 1 year and date<current_date+interval 2 year then amount else 0 end) as year2,
sum(case when date>=current_date+interval 2 year and date<current_date+interval 3 year then amount else 0 end) as year3,
sum(case when date>=current_date+interval 3 year and date<current_date+interval 4 year then amount else 0 end) as year4,
sum(case when date>=current_date+interval 4 year and date<current_date+interval 5 year then amount else 0 end) as year5
from table
group by id