Simple expressions with fields and query editor

I’m using an Influx data source and InfluxQL.
I often display data which is calculated with simple arithmetic expressions from the fields of a measurement, like differences or ratios. A simple example for a difference is

SELECT mean("dtq_50")-mean("dtq_min")
  FROM "TfcMonitor"
  WHERE ("host" =~ /^$host$/) AND $timeFilter
  GROUP BY time($__interval), "host", "oid" fill(null)

which gives combined with an ALIAS BY rule of $tag_host $tag_oid the data I want.

Simple to write down as InfluxQL query.
The math option seems only good for scale factors.
I wonder whether there is a way to generate such expressions with the query editor.