Why doesn't throw my function an exception??

Question

Ive written following function which converts dates into numbers represeting weekdays.
I want the function to throw an exception if a wrong value is given but whatever I try instead of an exception the only output by a wrong input is:
SQL> select day_calc('bla') from dual;
select day_calc('bla') from dual
ERROR at line 1:
ORA-01858: a non-numeric character was found where a numeric was expected
Anybody who knows why??
thx

Answer 1

If you want the function to accept the parameter and handle the exception, then you need to make your a_date varchar2.
You are missing "when others" after exception.
Your line "zahl := 3/0;" will always raise an exception. I assume that was added to try to force an exception for testing.
Please see the example below.
scott@ORA92> CREATE OR REPLACE FUNCTION day_calc
  2    (a_date     VARCHAR2)
  3    RETURN     NUMBER
  4  IS
  5    ergebnis NUMBER;
  6  BEGIN
  7    ergebnis := TO_NUMBER (TO_CHAR (TO_DATE (a_date, 'DD.MM.RRRR'), 'D')) - 1;
  8  --  zahl := 3/0;
  9    RETURN ergebnis;
10  EXCEPTION
11    WHEN OTHERS THEN RETURN -1;
12  END day_calc;
13  /
Function created.
scott@ORA92> SELECT day_calc ('bla') FROM DUAL
  2  /
DAY_CALC('BLA')
             -1
scott@ORA92> SELECT day_calc ('20.11.2004') FROM DUAL
  2  /
DAY_CALC('20.11.2004')
                     6
scott@ORA92>