use test;

delimiter //

drop function if exists test_fcn;
create function test_fcn(p_id bigint unsigned)
returns text
begin
	declare done boolean default false;
	declare first boolean default true;
	declare return_value text default '';
	declare id_ bigint unsigned default null;
	declare product_ varchar(255);	
	declare cursor_ cursor for select id, product from test.tbl where id < p_id order by id limit 100;
	declare continue handler for sqlstate '02000' set done = true;

	open cursor_;

		lp: loop
			fetch cursor_ into id_, product_;

			if done then 
				leave lp;
			end if;

			if first then
				# PROBLEM LINE
				set return_value = product_; #A
				#set return_value = concat(return_value, product_); #B
				set first = false;
			else		
				set return_value = concat(return_value, '|', product_);
			end if;
		end loop;

	close cursor_;

	return return_value;
end; //

delimiter ;