Mysql group by while using 3 data points while skipping first entry - mysql

Question

Im trying to write query to select data from table and group it by date and calculate average. It gets a bit complicated because i dont want to calculate average for all the data for certain date but only the 3 entries in descending order and also skip the first one.
I manage to write query for single date
select datum,datum_aladin,veter from napovedt where datum='2023-01-30' and spot='19' order by datum_aladin desc limit 1,3
which gives me returns:
datum |datum_aladin|veter|
----------+------------+-----+
2023-01-30| 2023013000| 4.0|
2023-01-30| 2023012918| 4.0|
2023-01-30| 2023012912| 4.5|
Now how do i get average for "veter" and write query to get this average value for all the dates in database ?

Answer 1

With MySQL 8 you might try:
Schema (MySQL v8.0)
CREATE TABLE napovedt
(`datum` datetime, `datum_aladin` int, `veter` decimal(8,3))
;
INSERT INTO napovedt
(`datum`, `datum_aladin`, `veter`)
VALUES
('2023-01-30 00:00:00', 2023013100, 2.0),
('2023-01-30 00:00:00', 2023013000, 4.0),
('2023-01-30 00:00:00', 2023012918, 4.0),
('2023-01-30 00:00:00', 2023012912, 4.5),
('2023-01-30 00:00:00', 1023013000, 3.0),
('2023-01-31 00:00:00', 2023013100, 5.0),
('2023-01-31 00:00:00', 2023013000, 4.0),
('2023-01-31 00:00:00', 2023012918, 2.0),
('2023-01-31 00:00:00', 2023012912, 1.5),
('2023-01-31 00:00:00', 1023013000, 3.0)
;
Query #1
with sq as (
select n.datum, n.veter, row_number () over (
partition by datum
order by datum_aladin desc
) rn
from napovedt n
)
select sq.datum, avg(sq.veter) from sq
where sq.rn between 2 and 4
group by sq.datum
order by sq.datum;
datum
avg(sq.veter)
2023-01-30 00:00:00
4.1666667
2023-01-31 00:00:00
2.5000000
View on DB Fiddle
If you do not have MySQL 8, you can then emulate PARTITION OVER with the following:
select sq.datum, avg(sq.veter) from (
select *, if(#prev <> datum, #rn:=0, #rn), #prev:=datum, #rn:=#rn+1 as rn
from napovedt, (select #rn:=0) as rn, (select #prev:='') as prev
order BY datum, datum_aladin desc
) sq
where sq.rn between 2 and 4
group by sq.datum
order by sq.datum;
datum
avg(sq.veter)
2023-01-30 00:00:00
4.1666667
2023-01-31 00:00:00
2.5000000
View on DB Fiddle