Use sum of three influxdb measurements as new measurement for query

I’m trying to calculate current power consumption and I need to use the integral function on the sum of three phases of current.

I’ve tried using the following query but it returned nothing.

SELECT mean(“cc1”) + mean(“cc2”) + mean(“cc3”) FROM (SELECT “value” AS “cc1” FROM “CC1”),
(SELECT “value” AS “cc2” FROM “device_frmpayload_data_CC2”),
(SELECT “value” AS “cc3” FROM “device_frmpayload_data_CC3”)
GROUP BY time(15s) fill(null)

Is there a way to get the sum from the three measurements and use the result in a query.

(Grafana 8.3.4)