with t1 as(
select 1 x from dual  union all
select -2 x from dual  union all
select 5 x from dual  union all
select 0 x from dual 
)
select x, case when x=0 then x
               when x>0 and x<5 then x*x
               when x<0 or x>5  then x*x*x
               else null
           end as result_s
from t1      

select x, case when x=0 then x
               when x>0 and x<5 then x*x
               when x<0 or x>5  then x*x*x
               else null
           end as result_s
from t1      

select x, case
               when x=>0 and x<5 then x*x
               when x<0 or x>5  then x*x*x
               else null
           end as result_s
from t1      

select x, decode(x,5,null, decode(sign(x)*sign(x-5),1,x*x*x,x*x)) result_s
from t1      

select x, case w when 5 then null
                       else Power(x,2+sign(sign(x)*sign(x-5)+1))
            end result_s
from t1