Oracle 18c

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CREATE OR REPLACE FUNCTION LISTNATION(N_NAME in VARCHAR2, R_NAME IN VARCHAR2, R_REGIONKEY IN NUMBER)
RETURN VARCHAR2 IS
R_REGIONKEY NUMBER(3);
R_NAME VARCHAR2(50)
N_NAME VARCHAR2(50);

BEGIN
select r_regionkey, r_name, n_name
from region
inner join nation
on r_regionkey = n_regionkey;

dbms_output.put_line = (R_REGIONKEY || " " || R_NAME || ":" || N_NAME || ",";

RETURN test;
END;
/
ORA-24344: success with compilation error

select * from user_errors;


NAME
TYPE
SEQUENCE
LINE
POSITION
TEXT
ATTRIBUTE
MESSAGE_NUMBER


LISTNATION
FUNCTION
1
5
1
PLS-00103: Encountered the symbol "N_NAME" when expecting one of the following:

   := ; not null default character

ERROR
103


create table region (r_regionkey, r_name) as
select 1, 'EMEA' from dual
union all
select 2, 'APAC' from dual
2 rows affected

create table nation (n_regionkey, n_name) as
select 1, 'FRANCE' from dual
union all
select 1, 'UNITED KINGDOM' from dual
union all
select 2, 'CHINA' from dual
3 rows affected

CREATE OR REPLACE FUNCTION LISTNATION(P_R_REGIONKEY IN NUMBER)
RETURN VARCHAR2 IS
  L_R_NAME REGION.R_NAME%TYPE;
  L_N_NAME NATION.N_NAME%TYPE;

BEGIN
  FOR l_row IN (
    select r.r_name, n.n_name
    from region r
    inner join nation n
    on r.r_regionkey = n.n_regionkey
    where r.r_regionkey = p_r_regionkey
  ) LOOP

    dbms_output.put_line (P_R_REGIONKEY || ' ' || l_row.R_NAME || ':' || l_row.N_NAME);

  END LOOP;

  RETURN 'test';
END;
/
declare
  l_result varchar2(50);
begin
  l_result := listnation(1);
  dbms_output.put_line('result: ' || l_result);
end;
/
1 rows affected

dbms_output:
1 EMEA:FRANCE
1 EMEA:UNITED KINGDOM
result: test