create or replace function fib(n) as (
  if ( n < 0, error('negative arguments not allowed'),
  (with recursive fib(i,e,f) as (
     select 1, 1, 1
     union all
     select i+1, e+f, e from fib
     where i <= n)
   select last(f order by i)
   from fib)
  )
);