Erro:PLS-00428:uma cláusula into é esperada nesta instrução select

create or replace function gettaxmin
            (period_tax_type_id in double precision, tax_range in number) 
    return double precision 
is
     Result double precision;
begin
  SELECT CASE WHEN max(tax_range) is null THEN 0 ELSE max(tax_range) END 
    INTO Result 
    FROM period_tax_rates WHERE (tax_range < 1) AND (period_tax_type_id = 2);
  return Result;
end gettaxmin;