Influx - Help to choose in between Tag and Field
You can take a call considering below two scenarios.


If you need to run a GROUPBY clause on a particular column/field, then you need to create it as Tag, otherwise you won't be able to use GROUPBY clause.
Indexing: Fields cannot be indexed in influxdb. Tag are automatically indexed.


Also, influx by default creates a 'time' tag, so it's better while inserting you pass the value to 'time' instead of adding an extra column called 'datetime'