SQL selecting average score over range of dates - mysql

Question

I have 3 tables:
doctors (id, name) -> has_many:
patients (id, doctor_id, name) -> has_many:
health_conditions (id, patient_id, note, created_at)
Every day each patient gets added a health condition with a note from 1 to 10 where 10 is a good health (full recovery if you may).
What I want to extract is the following 3 statistics for the last 30 days (month):
- how many patients got better
- how many patients got worst
- how many patients remained the same
These statistics are global so I don't care right now of statistics per doctor which I could extract given the right query.
The trick is that the query needs to extract the current health_condition note and compare with the average of past days (this month without today) so one needs to extract today's note and an average of the other days excluding this one.
I don't think the query needs to define who went up/down/same since I can loop and decide that. Just today vs. rest of the month will be sufficient I guess.
Here's what I have so far which obv. doesn't work because it only returns one result due to the limit applied:
SELECT
p.id,
p.name,
hc.latest,
hcc.average
FROM
pacients p
INNER JOIN (
SELECT
id,
pacient_id,
note as LATEST
FROM
health_conditions
GROUP BY pacient_id, id
ORDER BY created_at DESC
LIMIT 1
) hc ON(hc.pacient_id=p.id)
INNER JOIN (
SELECT
id,
pacient_id,
avg(note) AS average
FROM
health_conditions
GROUP BY pacient_id, id
) hcc ON(hcc.pacient_id=p.id AND hcc.id!=hc.id)
WHERE
date_part('epoch',date_trunc('day', hcc.created_at))
BETWEEN
(date_part('epoch',date_trunc('day', hc.created_at)) - (30 * 86400))
AND
date_part('epoch',date_trunc('day', hc.created_at))
The query has all the logic it needs to distinguish between what is latest and average but that limit kills everything. I need that limit to extract the latest result which is used to compare with past results.

Answer 1

Something like this assuming created_at is of type date
select p.name,
hc.note as current_note,
av.avg_note
from patients p
join health_conditions hc on hc.patient_id = p.id
join (
select patient_id,
avg(note) as avg_note
from health_conditions hc2
where created_at between current_date - 30 and current_date - 1
group by patient_id
) avg on t.patient_id = hc.patient_id
where hc.created_at = current_date;
This is PostgreSQL syntax. I'm not sure if MySQL supports date arithmetics the same way.
Edit:
This should get you the most recent note for each patient, plus the average for the last 30 days:
select p.name,
hc.created_at as last_note_date
hc.note as current_note,
t.avg_note
from patients p
join health_conditions hc
on hc.patient_id = p.id
and hc.created_at = (select max(created_at)
from health_conditions hc2
where hc2.patient_id = hc.patient_id)
join (
select patient_id,
avg(note) as avg_note
from health_conditions hc3
where created_at between current_date - 30 and current_date - 1
group by patient_id
) t on t.patient_id = hc.patient_id

Answer 2

SELECT SUM(delta < 0) AS worsened,
SUM(delta = 0) AS no_change,
SUM(delta > 0) AS improved
FROM (
SELECT patient_id,
SUM(IF(DATE(created_at) = CURDATE(),note,NULL))
- AVG(IF(DATE(created_at) < CURDATE(),note,NULL)) AS delta
FROM health_conditions
WHERE DATE(created_at) BETWEEN CURDATE() - INTERVAL 1 MONTH AND CURDATE()
GROUP BY patient_id
) t