Working with InfluxDB tags

[bibek687]

Requirement

I'd like to display a stacked bar chart of monthly overviews of no. of devices.
The InfluxDB schema is that we have tag for the month (not directly a "time" type, but a string from the script). Example is MonYear = SEP2020
There are Main device categories, and device subcategories, both stored as tag as well (e.g. MainDevice, SubDevice).
We have a field called value, which is 1 when there is a new addition and we sum/ count the value to get the total.
So, I'd like a chart which shows the number of devices in SubDevices of a particular MainDevice over each month.

Currently

My query is
SELECT sum("value") FROM "measurement" WHERE ("MainDevice" = 'External Device') AND $timeFilter GROUP BY "SubDevice", "MonYear"

With this, I just get the following. When I just use one group by tag, it works fine though.