Calculating values from the same table but a different period - sql

Question

I have a readings table with the following definition.
Column | Type | Collation | Nullable | Default
------------+-----------------------------+-----------+----------+--------------------------------------
id | integer | | not null | nextval('readings_id_seq'::regclass)
created_at | timestamp without time zone | | not null |
type | character varying(50) | | not null |
device | character varying(100) | | not null |
value | numeric | | not null |
It has data such as:
id | created_at | type | device | value
----+---------------------+--------+--------+-------
1 | 2021-05-11 04:00:00 | weight | 1 | 100
2 | 2021-05-10 03:00:00 | weight | 2 | 120
3 | 2021-05-10 04:00:00 | weight | 1 | 120
4 | 2021-05-10 03:00:00 | weight | 1 | 124
5 | 2021-05-01 22:43:47 | weight | 1 | 130
6 | 2021-05-01 15:00:48 | weight | 1 | 140
7 | 2021-05-01 13:00:48 | weight | 2 | 160
Desired Output
Given a device and a type, I would like the max and min value from the past 7 days for each matched row (active row ignored). If there's nothing in the past 7 days, then it should be 0.
id | created_at | type | device | value | min | max
----+---------------------+--------+--------+-------+-----+-----
1 | 2021-05-11 03:09:47 | weight | 1 | 100 | 120 | 124
3 | 2021-05-10 04:00:00 | weight | 1 | 120 | 124 | 124
4 | 2021-05-10 03:00:00 | weight | 1 | 124 | 0 | 0
5 | 2021-05-01 22:43:47 | weight | 1 | 130 | 140 | 140
6 | 2021-05-01 15:00:48 | weight | 1 | 140 | 0 | 0
I have created a db-fiddle.

Answer 1

You can use lateral left join for your requirement like below:
select
t1.id,
t1.created_at,
t1.type,
t1.device,
t1.value,
min(coalesce(t2.value,0)),
max(coalesce(t2.value,0))
from
readings t1
left join lateral
( select *
from readings
where id!=t1.id and created_at between t1.created_at- interval '7 day' and t1.created_at and device=t1.device and t1.type=type
) t2 on true
where t1.device='1' -- Change the device
and t1.type='weight' -- Change the type
group by 1,2,3,4,5
order by 1
DEMO

Answer 2

Considering the comments, here is your PSQL:
select readings.id, readings.type, readings.device, readings.created_at, readings.value,
min(COALESCE(m_readings.value,0)) min, max(COALESCE(m_readings.value,0)) max
from readings LEFT JOIN readings m_readings
ON m_readings.type =readings.type
AND m_readings.device =readings.device
AND m_readings.id > readings.id
AND date( m_readings.created_at) between (date(readings.created_at)-7) and date(readings.created_at)
group by readings.id, readings.type, readings.device, readings.created_at, readings.value
order by readings.id;
Explanations: We make a LEFT junction between each records of readings and the others records of readings which are of the same type and device but not the same id, keeping only the last 7 days records. Then for each type/devicewe are grouping to get max and min valueon this 7 days.

Answer 3

You should be using window functions for this!
select r.*,
max(value) over (partition by device, type
order by created_at
range between interval '7 day' preceding and interval '1 second' preceding
),
min(value) over (partition by device, type
order by created_at
range between interval '7 day' preceding and interval '1 second' preceding
)
from readings r;
The above returns NULL values when there are no values -- and that makes more sense to me than 0. But if you really want 0, just use COALESCE():
select r.*,
coalesce(max(value) over (partition by device, type
order by created_at
range between interval '7 day' preceding and interval '1 second' preceding
), 0),
coalesce(min(value) over (partition by device, type
order by created_at
range between interval '7 day' preceding and interval '1 second' preceding
), 0)
from readings r;
In addition to being more concise, this is easier to read and should have better performance than other methods.