Mysql Rank based on Avg - mysql

Question

I have a table with these columns
-----------------------------------------------------------------------
|id | deviceId | totalMethaneInGrams | totalFeedInMinutes | date |
-----------------------------------------------------------------------
|1 |141 | 402 |305 |2020-10-13 |
|2 |141 | 410 |368 |2020-10-13 |
|3 |145 | 361 |300 |2020-10-13 |
-----------------------------------------------------------------------
Now i want to calculate an average of totalMethaneInGrams and totalFeedInMinutes for a subset of devices. where date is less than some day. Group them by devicedId, order them by avg(totalMethaneInGrams) and get a global rank of those devices based on avg(totalMethaneInGrams).
This what i have up until now,
SELECT
deviceId,
ROUND(avg(totalFeedInMinutes),2) as methane,
ROUND(avg(totalMethaneInGrams)) as feed
FROM sensor_data
WHERE
deviceId IN (141,123,145) AND date < '2020-10-14'
GROUP BY deviceId
ORDER BY methane
Now what i don't understand is how to calculate global rank. My understanding is we need to calculate rank of all devices in the table. Then i can just search for the devices in the returned global dataset. Can it be done in a single query ?

Answer 1

mysql does not do rank over multiple columns well (eg feed within methane) a workaround is to do separately and join
SELECT t.deviceId,
ROUND(avg(totalMethaneInGrams),2) methane,
rank() over (order by ROUND(avg(totalMethaneInGrams),2 ) desc) as rankmethane,
max(feed) feed,
max(rankfeed) rankfeed
fROM t
join
(SELECT
deviceId,
ROUND(avg(totalFeedInMinutes)) as feed,
rank() over (order by ROUND(avg(totalFeedInMinutes),2 ) desc) as rankfeed
fROM t
WHERE deviceId IN (141,123,145) AND date < '2020-10-14'
group by deviceid) s
on s.deviceid = t.deviceid
WHERE t.deviceId IN (141,123,145) AND date < '2020-10-14'
GROUP BY t.deviceId ;
+----------+---------+-------------+------+----------+
| deviceId | methane | rankmethane | feed | rankfeed |
+----------+---------+-------------+------+----------+
| 141 | 406.00 | 1 | 337 | 2 |
| 145 | 361.00 | 2 | 400 | 1 |
+----------+---------+-------------+------+----------+
2 rows in set (0.002 sec)