Som så:
SELECT
turnover,
cost,
turnover - cost as profit
from (
(SELECT SUM(...) FROM ...) as turnover,
(SELECT SUM(...) FROM ...) as cost
) as partial_sums
Som så:
SELECT
turnover,
cost,
turnover - cost as profit
from (
(SELECT SUM(...) FROM ...) as turnover,
(SELECT SUM(...) FROM ...) as cost
) as partial_sums