Sort multiple fields consumes more CPU time and RAM

Hello everybody,

I have a little problem with some queries using multiple ORDER BY ...
ASC/DESC and they are really slow. I was thinking to do some mathematical
calculation in order to calculate the best ratio that will keep the order of
all my fields as if it was done with an usual multiple ORDER BY... sql
query.

The idea is to calculate that ratio in the SELECT query; and sort ONLY ONCE
the result of my query.

The ratio can be calculated from the LENGTH() of some VARCHAR fields, and
some other INT fiealds

Can somebody help with some maths please :)