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

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?

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

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?