Evaluate only one CASE WHEN in a select

Hi everybody,

I'm implementing something like this:

SELECT
    CASE WHEN add_numbers(t1.main_number,t2.main_number)>100
        THEN t1.description1
        ELSE t2.description1
    END AS number_description1,
    CASE WHEN add_numbers(t1.main_number,t2.main_number)>100
        THEN t1.description2
        ELSE t2.description2
    END AS number_description2
FROM table1 t1, table2 t2;

Is there a way to evaluate the 'CASE WHEN' only once?

Thanks

Daniel