how to find column as exception cause in oracle - oracle

Question

i have a table that the content of it:
ID A B
--- --- ----
1 123 &%df
2 587 364
A function was written to find invalid number(below script)
CREATE OR REPLACE FUNCTION is_number RETURN number IS
A_var number(15);
B_var number(15);
BEGIN
for u in (select id,
A,
B,
from TABLE_NAME) LOOP
BEGIN
select
to_number(u.A),
to_number(u.B),
into A_var , B_var
from dual;
EXCEPTION
WHEN others THEN
update TABLE_NAME set ?????? = null where id = u.id;
END;
END LOOP;
return -1;
END is_number;
the top script I want to replace ?????? to name of column as invalid number that in this example name of column is B
after excution top script,content of table is:
ID A B
--- --- ----
1 123
2 587 364

Answer 1

What if number conversion errors will be in both columns?
Try this:
create or replace function is_number return number is
a_var number(15);
b_var number(15);
function custom_to_number(v varchar2) return number is
result number;
begin
result:=to_number(v);
return result;
exception when others then
if(sqlcode = -6502) then
return null;
end if;
raise;
end;
begin
for u in (select id
,a
,b
from table_name)
loop
a_var:=custom_to_number(u.a);
b_var:=custom_to_number(u.b);
if((u.a is not null and a_var is null) or (u.b is not null and b_var is null)) then
update table_name
set a = case when a_var is null then null else a end
,b = case when b_var is null then null else b end
where id = u.id;
end if;
end loop;
return -1;
end is_number;

Answer 2

If your Intend is to replace the columns which contains alphanuneric data to NULL in the table, then you could use a Trigger to acheive this.
CREATE OR REPLACE TRIGGER trigger_Name BEFORE INSERT OR UPDATE OF
A_var, B_var ON TABLE_NAME
FOR EACH ROW
BEGIN
IF NOT((regexp_like (:NEW.A_var,'^[[:digit:]]+$'))) THEN
:NEW.A_var := NULL;
END IF;
IF NOT((regexp_like (:NEW.B_var,'^[[:digit:]]+$'))) THEN
:NEW.B_var := NULL;
END IF;
INSERT INTO TABLE_NAME(A_var, B_var) Values(:NEW.A_var, :NEW.B_var);
END;