Hello @cyclohexan,
Oof you are so right. Sorry, I should have double checked. I believe you want to use a sub query to calculate the mult value at each timestamp/row and then sum them together to get one sum value:
SELECT sum("mult") from ( SELECT "usage_system"*"usage_user" AS "mult" FROM "telegraf"."autogen"."cpu" WHERE time > :dashboardTime: AND "cpu"='cpu0')
