Exception PL/SQL - oracle

Question

Caution my english is horrible.
No one answers in the spanish forum.
doubts :
¿How can I control the exception of a empty entry? (Explanation following)
¿What value is saved in the variable if there's an empty entry?
I created this variable:
DECLARE
v_input NUMBER(8) := &entry;
I don't give a value, I mean in the pop up I accept directly without writing anything.
POPUP IMG
when I read the error code ( that I will leave at the end), I came across this line.
PLS-00103: Encountered the symbol ' ; ' when expecting one of the following :
So I guess the variable default value if you do a empty entry is -> ;
then I thought of controling the exception creating a IF, this if compares my variable (with empty entry/value) to ' ; ' you can see below.
BEGIN
DBMS_OUTPUT.PUT_LINE(v_codigo);
IF(v_codigo = ';')THEN
RAISE v_excepcion;
END IF;
EXCEPTION
when v_excepcion then
DBMS_OUTPUT.PUTLINE('No has insertado un valor válido');
END;
ERROR CODE
Informe de error -
ORA-06550: línea 2, columna 32:
PLS-00103: Se ha encontrado el símbolo ";" cuando se esperaba uno de los siguientes:
( - + case mod new not null <an identifier>
<a double-quoted delimited-identifier> <a bind variable>
continue avg count current exists max min prior sql stddev
sum variance execute forall merge time timestamp interval
date <a string literal with character set specification>
<a number> <a single-quoted SQL string> pipe
<an alternatively-quoted string literal with character set specification>
<an al
06550. 00000 - "line %s, column %s:\n%s"
*Cause: Usually a PL/SQL compilation error.
*Action:
sorry for my grammar mistakes, If it does not clear I will follow the post for give you more information.
thx

Answer 1

Exception handlers are for exceptions (errors) encountered during execution of your function or procedure or anonymous block. They don't handle syntax errors - where the function or procedure won't even compile.
You are using a substitution variable - one that is "substituted" (replaced) by your editor BEFORE the code is ever presented to the PL/SQL parser. THAT kind of error can't be anticipated and handled in the code - if you return nothing (an empty string) when prompted, the code itself will receive "nothing" in that place, and the syntax of your function or procedure will be incorrect, so you will get the syntax error you received. Your code looks exactly like this after the substitution:
v_input NUMBER(8) := ;
resulting exactly in the syntax error you have seen.
The correct way to pass in a value at run time is to use parameters (for functions or procedures), or bind variables in an anonymous block. The variable must be declared and initialized before executing the block (in a command line environment like SQL*Plus); or, in a GUI like Toad or SQL Developer, you will be prompted for a value for the bind variable. If you press Enter without giving a value, that is interpreted as NULL, which is perfectly valid. (Whether it is what you want or not, that's a different question.)
The code would have to look something like this:
declare
v_input number(8) := :entry; -- notice the leading colon :
begin
dbms_output.put_line(v_input);
end;
/
If you want to handle the case of NULL input, you would do it in code:
declare
v_input number(8) := :entry;
begin
if v_input is null then
-- handle it here
else
dbms_output.put_line(v_input); -- or whatever else you need to do
end if;
end;
/

Answer 2

You don't need exception to handle that; you could dbms_output.put_line (note that you used putline, which is wrong) within IF, or even raise_application_error if you want to stop execution. For example (valid value first):
SQL> declare
2 v_codigo varchar2(20) := '&entry';
3 begin
4 if v_codigo = ';' or v_codigo is null then
5 raise_application_Error(-20000, 'Invalid value');
6 else
7 dbms_output.put_line('You entered ' || v_codigo);
8 end if;
9 end;
10 /
Enter value for entry: Littlefoot
You entered Littlefoot
PL/SQL procedure successfully completed.
Invalid values: empty string and ;;
SQL> /
Enter value for entry:
declare
*
ERROR at line 1:
ORA-20000: Invalid value
ORA-06512: at line 5
SQL> /
Enter value for entry: ;
declare
*
ERROR at line 1:
ORA-20000: Invalid value
ORA-06512: at line 5
SQL>
Or, to reuse your own code: declare the exception first (line #3), then use it:
SQL> declare
2 v_codigo varchar2(20) := '&entry';
3 v_excepcion exception;
4 BEGIN
5 DBMS_OUTPUT.PUT_LINE(v_codigo);
6 IF(v_codigo = ';' or v_codigo is null) THEN
7 RAISE v_excepcion;
8 END IF;
9
10 EXCEPTION
11 when v_excepcion then
12 DBMS_OUTPUT.PUT_LINE('No has insertado un valor válido');
13 END;
14 /
Enter value for entry: Littlefoot
Littlefoot
PL/SQL procedure successfully completed.
SQL> /
Enter value for entry:
No has insertado un valor válido
PL/SQL procedure successfully completed.
SQL> /
Enter value for entry: ;
;
No has insertado un valor válido
PL/SQL procedure successfully completed.
SQL>