Decimal place require in Oracle - oracle

Question

case 1: SELECT TO_CHAR(12345.6789, '99999D99') FROM dual;
Output: 12345.67
case 2: SELECT TO_CHAR(12345.6789, '999D99') FROM dual;
Output: ######
case 3: SELECT TO_CHAR(12345, '99999D99') FROM dual;
Output: 12345.00
case 4: SELECT TO_CHAR(12345.1, '99999D99') FROM dual;
Output: 12345.10
Here Problem is if we don't know how many digits before decimal then how to manage for correct answer.[only case 1,3,4 can resolved using by TO_CHAR but how to solve for case 2.]

Answer 1

In this case the simplest answer might be to not supply a format model at all, but truncate or round the value to two decimal places:
SELECT TO_CHAR(ROUND(12345.6789, 2)) as rounded,
TO_CHAR(TRUNC(12345.6789, 2)) as truncated
FROM dual;
ROUNDED TRUNCATED
-------- ---------
12345.68 12345.67
From the documentation:
If you omit fmt, then n is converted to a VARCHAR2 value exactly long enough to hold its significant digits.
Otherwise you'd need to supply a format model that allowed for the maximum size of your number; if it's unrestricted you'd need 36 nines, the decimal separator, and two more nines. The result would be padded with spaces so you might also want to trim it, depending on how you'll use the string value.
SELECT TO_CHAR(12345.6789, '999999999999999999999999999999999999D99') as val
FROM dual;
VAL
----------------------------------------
12345.68
You could also do that flexibly by using the length of the truncated value (i.e. once the decimal places have been removed):
SELECT TO_CHAR(12345.6789,
lpad('9', length(trunc(12345.6789)), '9') || 'D99') as val
FROM dual;
VAL
---------
12345.68
But that seems unnecessarily complicated when you can let Oracle work it out for you.
However, if you want the decimals to show trailing zeros then you might need to use that method; but with zeros after the decimal separator:
SELECT TO_CHAR(12345.6, lpad('0', length(trunc(12345.6)), '9') || 'D00') as val
FROM dual;
VAL
---------
12345.60
... which addresses the 3rd and 4th cases you added. I've made it show a leading zero for values less than 1 as well; the generated format model in this case is '99990D00'. The number of nines will still vary depending on the size of your number.
By default Oracle still leaves a space at the start for a potential minus sign. You can avoid that with the FM format modifier:
SELECT TO_CHAR(12345.6, 'FM'
|| lpad('0', length(trunc(12345.6)), '9') || 'D00') as val
FROM dual;
VAL
--------
12345.60

Answer 2

You could always go with the maximum number of digits you expect to be present in the input. If there are fewer digits in the input than your format specifier, it wouldn't affect the outcome in anyway. For instance,
select to_char(12323.5553,'99999D99') from dual
would produce,
123.56

Answer 3

As you said, the length of the input is unknwon. So why would you use a fixed length formater for somthing that is unknown? Does not work. Read your input as String from the beginning and manipulate it as String or even better - BLOB.
Well, to do the rounding correct might be tricky.
So, best check your data if the numbers will realy get so big, because that would mean a lot of work and trouble.
If not more than 38 Digits are needed, you can go with decimal or numeric datatype and (if you insist on a formatter) use the TM formatter for example.
SELECT to_char(cast(1234.456 as decimal( *,2)), 'TM') as a FROM dual
or take the advice that was given above by the other posters.