List all tags with missing values for a certain field, in Flux

Fluxlang
, ,
1

In Influx 2.x, using Flux, is there a way to report all distinct tags which have missing (null) data in certain fields?

Simply put, I want to list all ‘hardware_id’ keys which don’t have a value for field ‘heading’.

In plain old SQL, and perhaps Influx QL in v1.x, it would be the equivalent of something like this in pseudo code:

	# omited time range for brevity
	SELECT device_id
	FROM measurement 
	WHERE field = 'heading'
	AND _value is null;

I’ve tried fill()-ing it, to no avail:

from(bucket: "sandbox")
    |> range(start: v.timeRangeStart, stop: v.timeRangeStop)
    |> filter(fn: (r) => r["_measurement"] == "metrics")
    |> filter(fn: (r) => r["_field"] == "heading")
	
    // fill empty records with an arbitrary value
    |> fill(column: "_value", value: -999.0)

    // attempt to filter on these empty records
    |> filter(fn: (r) => r["_value"] == -999.0)

And I’ve also noticed the exists operation, but the documentation part is unclear for me on how this can be applicable:

from(bucket: "sandbox")
    |> range(start: v.timeRangeStart, stop: v.timeRangeStop)
    |> filter(fn: (r) => r["_measurement"] == "metrics")
    |> filter(fn: (r) => r["_field"] == "heading")
    |> filter(fn: (r) => ({
	      r with
	      human_readable:

	      	// does not work, not sure if this even makes sense?
	        if exists r._value then r["foo"] = true
	        else r["foo"] = false
    }))

Any help would be very much appreciated.

2

Hello @moriarty,
I believe you can just do:

|> from(bucket: "my bucket")
|> filter(fn: (r) =>  r._measurement == "measurement")
|> filter(fn: (r) =>  r._field == "heading")
|> filter(fn: (r) =>  not exists r._value)
|> group()
|> unique(column: "device_id")
3

I am searching for a suitable predicate to delete data where a specific tag (here: “item”) doesnt exist.
I can query the data with the not exists operator but i can not delete it with

curl --request POST http://.../api/v2/delete\?org\=...\&bucket\=... \
  --header 'Authorization: Token ...' \
  --header 'Content-Type: application/json' \
  --data '{
    "start": "2019-01-01T00:00:00Z",
    "stop": "2024-01-01T00:00:00Z",
    "predicate": "_measurement=\"name\" AND not exists item"
  }'

but i didnt find a documentation how to do this with the CLI approach. Can you give a hint?