Combine (sum) 2 items (values) in InfluxDB to new item

Add-ons Persistence Services
1

I have 2 different items (electricity-use in day + electricity-use at night) with are persisted in InfluxDB (for a long time alread).

Now I want to create a new item (electricity-use) which would be the sum of both items. I can do this via a rule for newly created values, but I would also like to do this for the historical values.

Any advice on how to do this?

2

IMHO this is the task that can be done using openHAB. IMHO your desired task i outside the scipe of opnHAB

3

I’m also reading a lot in the difference influxdb forums. But didn’t find the answer yet.

Should I first create the new item in OH + the rule, and then ‘fill in’ the old data? Or the other way around?