Need Function to return CHAR(2) datatype -

Question

I've created the following function. It needs to return a CHAR(2) datatype, but this code always returns VARCHAR2(4000). If I change it to numeric, I do get a number.
Is there some obvious reason why I am not able to return a 2-byte character value
from this code (I have tried substring and cast, but have not been able to transform
the result.)?
CREATE OR REPLACE function bal_fy_mon_seq (sysdate IN date)
RETURN CHAR
IS
bal_fy_mon_seq CHAR(2);
BEGIN
SELECT
DECODE
(TO_CHAR(SYSDATE,'MM'),'01','11',
'02','12',
'03','01',
'04','02',
'05','03',
'06','04',
'07','05',
'08','06',
'09','07',
'10','08',
'11','09',
'10' )
     INTO bal_fy_mon_seq
from dual;
RETURN (bal_fy_mon_seq);
END;
/

Answer 1

That works nicely as documentation, but it does not actually restrict the length of the return value from the function:
SQL> CREATE PACKAGE my_pkg AS
  2     SUBTYPE char_2 IS CHAR(2);
  3  END;
  4  /
Package created.
SQL> CREATE FUNCTION my_funct
  2     RETURN my_pkg.char_2 is
  3  BEGIN
  4     RETURN 'aaaa';
  5  END;
  6  /
Function created.
SQL> SELECT LENGTH(my_funct) FROM dual;
LENGTH(MY_FUNCT)
               4The only way to enforce a length limit on the return value of a function is to check in the function itself. Alternatively, if you declare the variable that receives the return value correctly (i.e. as whatever you want the return limited to), you will get an error if the length is not correct:
SQL> DECLARE
  2     l_v CHAR(2);
  3  BEGIN
  4     l_v := my_funct;
  5  END;
  6  /
DECLARE
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error: character string buffer too small
ORA-06512: at line 4Now, just trap the error and take whatever action seems appropriate.
TTFN
John