select avg for specific values of date - sql

Question

I have this table 'meteorecords' with date, temperature, rh and the meteo station which made the record.
rerowid date temp rh meteostid
1 2019-09-9 28.8 55.6 AITNIA2
2 2019-09-10 30.3 51.3 AITNIA2
3 2019-09-11 28.6 49.0 AITNIA2
4 2019-09-12 26.7 51.9 AITNIA2
5 2019-09-13 25.3 48.1 AITNIA2
6 2019-09-14 25.3 38.5 AITNIA2
7 2019-09-15 25.0 42.2 AITNIA2
8 2019-09-16 24.1 52.1 AITNIA2
9 2019-09-17 23.3 65.2 AITNIA2
10 2019-09-18 22.7 72.2 AITNIA2
11 2019-09-19 23.4 73.9 AITNIA2
12 2019-09-20 23.1 76.7 AITNIA2
13 2019-09-21 22.5 60.3 AITNIA2
14 2019-09-22 20.9 61.6 AITNIA2
15 2019-09-23 21.9 73.9 AITNIA2
16 2019-09-24 23.2 79.6 AITNIA2
17 2019-09-25 21.8 73.6 AITNIA2
18 2019-09-26 22.2 77.6 AITNIA2
19 2019-09-27 22.9 77.1 AITNIA2
20 2019-09-28 22.8 68.4 AITNIA2
21 2019-09-29 22.6 75.5 AITNIA2
...........................
I want to select all the fields plus the average temperature of the last 3 days.
I'm using postgresql because I have some geometric and spatial data in the db.
I tried this with no luck:
SELECT rerowid,redate,retemp,rerh,meteostid,
(SELECT AVG(retemp)
FROM meteorecords m
WHERE meteostid = m.meteostid AND m.redate BETWEEN redate-2 AND redate)
FROM meteorecords
which returns a result like this:
rerowid date temp rh meteostid AVG_Last_3_Days
1 2019-09-09 28.8 55.6 AITNIA2 22.2824
2 2019-09-10 30.3 51.3 AITNIA2 22.2824
3 2019-09-11 28.6 49.0 AITNIA2 22.2824
4 2019-09-12 26.7 51.9 AITNIA2 22.2824
5 2019-09-13 25.3 48.1 AITNIA2 22.2824
6 2019-09-14 25.3 38.5 AITNIA2 22.2824
7 2019-09-15 25.1 42.2 AITNIA2 22.2824
..................
But I want a result like this:
rerowid date temp rh meteostid AVG_Last_3_Days
1 2019-09-09 28.8 55.6 AITNIA2 28.8
2 2019-09-10 30.3 51.3 AITNIA2 29.5
3 2019-09-11 28.6 49.0 AITNIA2 29.2
4 2019-09-12 26.7 51.9 AITNIA2 28.5
5 2019-09-13 25.3 48.1 AITNIA2 26.9
6 2019-09-14 25.3 38.5 AITNIA2 25.8
7 2019-09-15 25.1 42.2 AITNIA2 25.2
..................

Answer 1

Use window functions. If you have one row per date or you want the previous three dates *in the data):
SELECT rerowid, redate, retemp, rerh, meteostid,
AVG(retemp) OVER (PARTITION BY meteostid ORDER BY redate ROWS BETWEEN 2 PRECEDING AND CURRENT ROW) as avg_retemp_3
FROM meteorecords;
If you want 3 chronological days, use RANGE:
SELECT rerowid, redate, retemp, rerh, meteostid,
AVG(retemp) OVER (PARTITION BY meteostid
ORDER BY redate
RANGE BETWEEN '2 DAY' PRECEDING AND CURRENT ROW) as avg_retemp_3
FROM meteorecords;