Why is the output only the last value? Oracle loop cursor - oracle

Question

I'm trying to output a list of the courses a professor teaches, by receiving the prof's id by parameter to my function, and showing all courses, each separated by a comma. For example, if a Professor teaches Humanities, Science and Math, I want the output to be: 'Humanities, Science, Math'. However, I'm getting just 'Math,'. It only shows the last field that it found that matched with the prof's id.
CREATE OR REPLACE FUNCTION listar_cursos(prof NUMBER) RETURN VARCHAR
IS
CURSOR C1 IS
SELECT subject.name AS name FROM subject
INNER JOIN course_semester
ON subject.id = course_semester.id_subject
WHERE course_semester.id_profesor = prof
ORDER BY subject.name;
test VARCHAR(500);
BEGIN
FOR item IN C1
LOOP
test:= item.name ||',';
END LOOP;
RETURN test;
END;
/
I am aware that listagg exists, however I do not wish to use it.

Answer 1

In your loop, you re-assign to the test variable, instead of appending to it. This is why, at the end of the loop, it will just hold the last value of item.name.
The assignment should instead be something like
test := test || ',' || item.name
Note also that this will leave a comma at the beginning of the string. Instead of returning test, you may want to return ltrim(test, ',').
Note that you don't need to declare a cursor explicitly. The code is easier to read (in my opinion) with an implicit cursor, as shown below. I create sample tables and data to test the function, then I show the function code and how it's used.
create table subject as
select 1 id, 'Humanities' name from dual union all
select 2 , 'Science' from dual union all
select 3 , 'Math' from dual
;
create table course_semester as
select 1 id_subject, 201801 semester, 1002 as id_profesor from dual union all
select 2 , 201702 , 1002 as id_profesor from dual union all
select 3 , 201801 , 1002 as id_profesor from dual
;
CREATE OR REPLACE FUNCTION listar_cursos(prof NUMBER) RETURN VARCHAR IS
test VARCHAR(500);
BEGIN
FOR item IN
(
SELECT subject.name AS name FROM subject
INNER JOIN course_semester
ON subject.id = course_semester.id_subject
WHERE course_semester.id_profesor = prof
ORDER BY subject.name
)
LOOP
test:= test || ',' || item.name;
END LOOP;
RETURN ltrim(test, ',');
END;
/
select listar_cursos(1002) from dual;
LISTAR_CURSOS(1002)
-----------------------
Humanities,Math,Science