How to reuse a result column in an expression for another result column

Question

Example:

SELECT
   (SELECT SUM(...) FROM ...) as turnover,
   (SELECT SUM(...) FROM ...) as cost,
   turnover - cost as profit

Sure this is

Answer 1

Perhaps the sql "with" clause could help, as presented here http://orafaq.com/node/1879 (other databases such as Postgres do it as well, not just oracle).