PL/SQL : i have a function but there is an error : "in a procedure,RETURN can not contain an expression" - oracle

Question

Here is my code:
CREATE OR REPLACE FUNCTION customer_city_function(city_in IN VARCHAR2)
RETURN NUMBER
AS
number_cus NUMBER := 0;
CURSOR cus_cur IS
SELECT COUNT(*)
FROM customer
WHERE customer_city = city_in;
BEGIN
IF city_in IS NOT NULL THEN
OPEN cus_cur;
FETCH cus_cur INTO number_cus;
CLOSE cus_cur;
END IF;
RETURN number_cus;
END;
/
and here is warnings:
Error starting at line : 1 in command -
CREATE OR REPLACE FUNCTION customer_city_function(city_in IN VARCHAR2)
RETURN NUMBER
AS
number_cus NUMBER := 0
Error report -
SQL Command: functıon CUSTOMER_CITY_FUNCTION
Failed: Warning: executing is completed with a warning
Error starting at line : 5 in command -
CURSOR cur_cur IS
Error report -
Unknown Command
Error starting at line : 6 in command -
SELECT COUNT(*)
FROM costumer
WHERE customer_city=city_in
Error at Command Line : 8 Column : 25
Error report -
SQL Error: ORA-00904: "CITY_IN": undefined variable
00904. 00000 - "%s: invalid identifier"
*Cause:
*Action:
Error starting at line : 9 in command -
BEGIN
IF city_in IS NOT NULL
THEN
OPEN cus_cur;
FETCH cus_cur INTO number_cus;
CLOSE cus_cur;
END IF;
RETURN (number_cus);
END;
Error report -
ORA-06550: row 2, column 6:
PLS-00201: 'CITY_IN' variable should been defined
ORA-06550: row 2, column 3:
PL/SQL: Statement ignored
ORA-06550: row 8, column 1:
PLS-00372: in a procedure, RETURN can not contain an expression
ORA-06550: row 8, column 1:
PL/SQL: Statement ignored
06550. 00000 - "line %s, column %s:\n%s"
*Cause: Usually a PL/SQL compilation error.
*Action:
Where is my mistake? I can't find it, it doesn't make any sense.
(I translated this warning message from my language. I hope I did it right.)
I have just tried it in Command Window and it works. Why doensn't it work in Oracle SQL Developer sql worksheet?

Answer 1

There is nothing wrong with your posted code. The issue might be with your client or the way you are compiling the code.
As you have mentioned PL/SQL Developer in the tags, it might be possible that you have some extra characters in the SQL Worksheet and you are compiling the function as a script, thus the compiler finds it erroneous.
Here is a demo in SQL*Plus, and there is no error:
SQL> CREATE OR REPLACE FUNCTION customer_city_function(i_deptno IN number)
2 RETURN NUMBER
3 AS
4 number_cus NUMBER := 0;
5 CURSOR cus_cur IS
6 SELECT COUNT(*)
7 FROM emp
8 WHERE deptno=i_deptno;
9 BEGIN
10 IF i_deptno IS NOT NULL
11 THEN
12 OPEN cus_cur;
13 FETCH cus_cur INTO number_cus;
14 CLOSE cus_cur;
15 END IF;
16 RETURN number_cus;
17 END;
18 /
Function created.
SQL> sho err
No errors.
SQL> SELECT customer_city_function(10) FROM DUAL;
CUSTOMER_CITY_FUNCTION(10)
--------------------------
3
SQL>
The only difference in my code is that I have used EMP table instead of CUSTOMERS table and the input parameter is DEPTNO instead of CITY_IN. Rest everything is same and function compiles and executes without any errors.