ORA-06502 use TO_NUMBER and TO_CHAR

Question

Hi,
Oracle Database 10g 10.2.0.5.0.
I have mistake in this code:
nSuper_ NUMBER(6,2);
dbms_output.put_line('Super: ' ||  TO_NUMBER(nSuper_,'FM9G990D90'));
...I should use "TO_CHAR"...but my test is not failure, why?:
--a)
SET SERVEROUTPUT ON
DECLARE
  nSuper_ NUMBER(6,2);
BEGIN
  nSuper_ := 666.12;
  dbms_output.put_line('Super: ' ||  TO_NUMBER(nSuper_,'FM9G990D90'));
END;
Super: 666,12
--b)
SET SERVEROUTPUT ON
DECLARE
  nSuper_ NUMBER(6,2);
BEGIN
  nSuper_ := 6666.12;
  dbms_output.put_line('Super: ' ||  TO_NUMBER(nSuper_,'FM9G990D90'));
END;
DECLARE
ERROR en línea 1:
ORA-06502: PL/SQL: error  numérico o de valor
ORA-06512: en línea 5
--c)
SET SERVEROUTPUT ON
DECLARE
  nSuper_ NUMBER(6,2);
BEGIN
  nSuper_ := 6666.12;
  dbms_output.put_line('Super: ' ||  TO_CHAR(nSuper_,'FM9G990D90'));
END;
Super: 6.666,12Why "a" not fail and "b" if it fails?

Answer 1

Hi,
jortri wrote:
Why "a" not fail and "b" if it fails?Because Oracle RDBMS is (too) kind to you for "simple" conversion like that (but that doesn't mean you won't get errors...).
The to_number function takes as input <b>string</b>.
You're sending to it a <b>number</b>, so Oracle does this : +"Ok this guy is sending a number into a TO_NUMBER function when it should be a string, let's do an implicit conversion for him transparently"+.
Your to_number(my_number_variable,'FM9G990D90') actually becomes this :to_number( to_char(my_number_variable) ,'FM9G990D90')But, as you can notice, the to_char function is not given any format, so it uses your session default which could be way different from the mask you're providing to the to_number function.
Please execute this to understand what your failing to_number function is receiving as input :select 6666.12 number_implicitly_converted from dual;By default, on my machine it displays this :Scott@my11g SQL>select 6666.12 number_implicitly_converted from dual;
NUMBER_IMPLICITLY_CONVERTED
                    6666.12Now if I use it as input of your to_number function with your format mask :Scott@my11g SQL>select TO_NUMBER('6666.12','FM9G990D90') back_to_number from dual;
select TO_NUMBER('6666.12','FM9G990D90') back_to_number from dual
ERROR at line 1:
ORA-01722: invalid numberTadammm !
Conclusion : Don't mess up the use of to_number/to_char/to_date functions.
:-)