The problem is in your column references. You do not need to prefix columns with the schema, just with the alias. Also, your subquery does not have the field "value"; I think you may have transposed fields. Try this:
INSERT INTO db.my_new_table
SELECT a.id,
a.factor * b.value AS myValue
FROM (
SELECT id, SUM(value) AS factor
FROM db.table0
GROUP by id
) AS a
JOIN db.table2 AS b
ON a.id = b.id;