Storing multiple parameters into one variable Oracle 11G - oracle

Question

I am working on an assignment. What I want to do is store two parameter values into one variable value. My code at the moment is this:
create or replace function generateISIN(
countryCode Country.Code%type,
universityCode University.Code%type,
studentNumber varchar2)
return varchar2
as
v_numbers varchar2(9);
newStudentNumber varchar2(50) := '';
begin
select co.code, un.code
into newStudentNumber
from country co, university un
where v_numbers = studentNumber;
dbms_output.put_line('implementeer deze functie verder...');
return newStudentNumber;
end;
/
The meaning of this program/code is to get the country code (US, NL, AUS, etc..) and the university code (RUS, TUE, TIU, etc..) into one variable. So in the end I will get a ISIN
International Student Identification Number
For example: NL 1234 5678 944 TUE
Any idea how to combine the country code and university code with a number?

Answer 1

Assuming your variable is big enough to hold the result, you can simply concatenate the columns using the string concatenation operator ||:
select co.code || un.code
into newStudentNumber
from country co, university un
where v_numbers = studentNumber;

Answer 2

You could simply concatenate the column values using the concatenate operator || or the CONCAT function.
For example,
select co.code ||' '|| un.code
into newStudentNumber
from country co, university un
where v_numbers = studentNumber;
I have used a space in between just to make sure that the output is clear and each code is separated by a space.
Update You need to correct your query:
select co.code, un.code
into newStudentNumber
from country co, university un
where v_numbers = studentNumber;
You have a Cartesian join since the filter predicate has no real column(s)
On both sides of the operator you have used the local variable, makes no sense. Usually, you would do a comparison in a IF-ELSE construct based on the business logic.
dbms_output.put_line('implementeer deze functie verder...');
DBMS_OUTPUT is a good help while testing your code, however, make sure you don't carry it on production environment.
Also, remember, if you could do something in SQL, then you should not use PL/SQL unless there is a business need. Your entire code could be replaced with a single SQL statement.