"Safe" TO_NUMBER()

SELECT TO_NUMBER('*') FROM DUAL

This obviously gives me an exception:

ORA-01722: invalid number

Is there a way to "skip" it and get 0 or NULL instead?

The whole issue: I have NVARCHAR2 field, which contains numbers and not almost ;-) (like *) and I need to select the biggest number from the column.

Yes, I know it is a terrible design, but this is what I need now... :-S

UPD:

For myself I've solved this issue with

COALESCE(TO_NUMBER(REGEXP_SUBSTR(field, '^\d+')), 0)

Solution 1:

From Oracle Database 12c Release 2 you could use TO_NUMBER with DEFAULT ... ON CONVERSION ERROR:

SELECT TO_NUMBER('*' DEFAULT 0 ON CONVERSION ERROR) AS "Value"
FROM DUAL;

Or CAST:

SELECT CAST('*' AS NUMBER DEFAULT 0 ON CONVERSION ERROR) AS "Value"
FROM DUAL;

db<>fiddle demo

Solution 2:

COALESCE(TO_NUMBER(REGEXP_SUBSTR(field, '^\d+(\.\d+)?')), 0) 

will also get numbers with scale > 0 (digits to the right of the decimal point).

Solution 3:

I couldn't find anything better than this:

function safe_to_number(p varchar2) return number is
    v number;
  begin
    v := to_number(p);
    return v;
  exception when others then return 0;
end;

Solution 4:

select COALESCE(TO_NUMBER(REGEXP_SUBSTR( field, '^(-|+)?\d+(\.|,)?(\d+)?$')), 0) from dual;

It will convert 123 to 123, but 123a or 12a3 to 0.