how to conditionally select variables?

I have a table with 2 variables - X and Y. I wish to conditionally select X OR Y, depending on the month, as such:

DATA test ;
    SET work.Final_union ;
    IF 1 <= MONTH(TODAY()) <= 5
    THEN output  ;
    IF 6 <= MONTH(TODAY()) <= 12
    THEN output ;
RUN ;

where do I put the selected variables?