create or replace function f_test(type_in in varchar2,startdate_in in varchar2)
return int is 
  i_num int;
begin
  execute immediate 'select sum(total) from table where type='''||type_in||
                    ''' and '||startdate_in into i_num;
  return i_num;
end;

------解决方案--------------------
type这列的值是什么？
下面这句：select sum(total) from 表 where type=type_in || startdate_in  
应该是这样的吧：
select sum(total) from 表 where type=type_in and startdate_in  
对吧？

------解决方案--------------------
2楼的动态SQL很好用：
探讨

SQL code

create or replace function f_test(type_in in varchar2,startdate_in in varchar2)
return int is 
  i_num int;
begin
  execute immediate 'select sum(total) from table where type='''||type……


------解决方案--------------------
SQL code

CREATE OR REPLACE FUNCTION get_sql(type_in VARCHAR2,startdate_in VARCHAR2)
RETURN NUMBER IS res NUMBER(10,2);
BEGIN
       out_sql:='select sum(total) from tab where type ='||type_in||' and '|| startdate_in;
       EXECUTE IMMEDIATE out_sql INTO  res;
       RETURN res;
END