Hi,
I am currently trying to display difference of results from 2 sensors in a Grafana panel.
In my InfluxDB database I have a measurement that holds values of both sensors:
> SELECT * FROM "Vergleich" WHERE time>now()-2m
name: Vergleich
time rh_dht22 rh_tfa temp_dht22 temp_tfa tp_dht22 tp_tfa
---- -------- ------ ---------- -------- -------- ------
1611407400000000000 45 21.883333333333333 9.40611175608533
1611407433000000000 47 21.3 9.5
1611407460000000000 45 21.833333333333332 9.360802312324173
1611407493000000000 47 21.2 9.4
For both sensors (DHT22 and some TFA device) I have stored 3 values each. They are not provided with identical timestamp but that should not be a problem.
I want to calculate the difference to see how well the various sensors provide similar data.
I am able to get some useful data out of influx:
> SELECT mean("temp_dht22") - mean("temp_tfa") AS "d_temp_dht22" FROM "Vergleich" WHERE time>now()-5m GROUP BY time(60s) fill(null)
name: Vergleich
time d_temp_dht22
---- ------------
1611407220000000000
1611407280000000000 -0.6000000000000014
1611407340000000000 -0.6000000000000014
1611407400000000000 -0.5833333333333321
1611407460000000000 -0.6333333333333329
1611407520000000000
I got this query string from Calculate difference between two measurements and [VERY NEWBIE ] Show difference between two graphs values
Unfortunately I am not able to add this to my Grafana panel.
If I add a query and enter this code
SELECT mean("temp_dht22") - mean("temp_tfa") AS "d_temp_dht22" FROM "Vergleich" WHERE $timeFilter GROUP BY time($__interval) fill(null)
it is automatically changed to
SELECT "temp_dht22" -, "temp_tfa" AS "d_temp_dht22" FROM "Vergleich" WHERE $timeFilter GROUP BY time($__interval) fill(null)
and the graph only shows “No data”.
My Grafana version is “v7.3.7 (1e261642f4)” and I run it on a Raspberry 3+ with RaspiOS Buster (Image from 2020-12-02).
Any hints how to insert the query into the fields of my panel is welcome.