InfluxDB 2.x: Error: Unsupported input type for mean aggregate (string to integer)

THIS ERROR HAS NO SOLUTION RIGHT NOW, MORE INFORMATION IN THE GITHUB ISSUE: https://github.com/influxdata/influxdb/issues/20980

My InfluxDB 2.x downsampling tasks could not run because of following error.

Error

Could not execute task run; Err: unsupported input type for mean aggregate: string: unsupported input type for mean aggregate: string
Unsupported input type for mean aggregate: string

Cause

This error occurs because of type conflicts in the same fields respectively in the value of it.

Solution / Workaround

Unfortunately InfluxDB 2.x has no solution for this (or I don't know about them).
That's why we have to convert the type of the "_value" fields and rewrite this in a new measurement.

• Optionally: Create a new bucket (I called them "typeconversion")
• Write a query that selects your measurement, convert the values to integer and rewrite the data to your new bucket:

datatoconvert = from(bucket: "telegraf")
  |> range(start: v.timeRangeStart, stop: v.timeRangeStop)
  |> filter(fn: (r) => r._measurement == "asset_vm_cmdb")
  |> toInt()

datatoconvert
  |> filter(fn: (r) => exists r._value)
  |> to(bucket: "typeconversion", org: "<YOUR_ORG>")

• Remove the old measurement