# Declaration for the sake of euler_table()
create or replace function cooling(x,y) as NULL;

# Euler method assuming cooling/2 is available
create or replace function euler_table(x_start, y_start, x2, h) as table (
  with recursive cte as (
    select x_start::DOUBLE as x, y_start::DOUBLE as y
    union all
    select x + h as x,
           y + h*cooling(x, y)
    from cte
    where (x < x2 and x_start < x2) or
          (x > x2 and x_start > x2)
  )
  from cte
);

create or replace function euler(x_start, y_start, x2, h) as (
  select last(y order by x) from euler_method(x_start, y_start, x2, h)
);

## Example:
create or replace function cooling(x,y) as
  -0.07 * (y - 20);

select h, euler(0,100, 100, h) from unnest([1,2,5,10,20]) _(h);