Hi all, I'm a newbie of SQL and influxdb; me and a colleague are trying to
create a montoring system of field data such as temperatures, energy and so
on, in order to work on some real use cases and test the use and learn the
basis of influxdb and grafana.
We are quite satisfied with the basic monitoring so we are going to go
further in learning and we like to use influx SQL to analyze the collected
data and we are experiencing our first "wall".
Use case
we have a field with values only 0/1, that represent, for example, the
presence of a flame in a burner (burner ON/OFF) that is stored every 5 min.
We'd like to find the exact time where the flame was turned ON/OFF so we
have tested this query:
SELECT DIFFERENCE("vieBurnerFlame") as ch FROM "gInfluxTemperatures" WHERE
(time >= now() - 1d)
and the result (frgmer follow) is ok, you cas see ch calculated field as
1/-1 as ON FLAME/OFF FLAME:
time ch
2016-08-29T17:15:00.201Z 0
2016-08-29T17:20:00.185Z 1
2016-08-29T17:25:00.201Z 0
2016-08-29T17:30:00.232Z -1
2016-08-29T17:35:00.216Z 0
Further i've tryed to filter out only the "event", referring to previous
example the idea is to have only the 2 points:
2016-08-29T17:20:00.185Z 1
2016-08-29T17:30:00.232Z -1
so i've used the query:
SELECT DIFFERENCE("vieBurnerFlame") as ch FROM "gInfluxTemperatures" WHERE
(time >= now() - 1d) and ch <> 0
but the results set was the same. The opposite test:
SELECT DIFFERENCE("vieBurnerFlame") as ch FROM "gInfluxTemperatures" WHERE
(time >= now() - 1d) and ch = 0
returns no data (as expected from previous result).
I kindly ask why i'm getting this result and how to achieve the gola.
Thank a lot for support.
f
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