What is the default Precision and Scale for a Number in Oracle?

Question

When creating a column of type NUMBER in Oracle, you have the option of not specifying a precision or scale. What do these default to if you don't specify them?

Answer 1

I believe the default precision is 38, default scale is zero. However the actual size of an instance of this column, is dynamic. It will take as much space as needed to store the value, or max 21 bytes.

Answer 2

NUMBER (precision, scale)

If a precision is not specified, the column stores values as given. If no scale is specified, the scale is zero.

A lot more info at:

http://download.oracle.com/docs/cd/B28359_01/server.111/b28318/datatype.htm#CNCPT1832

Answer 3

Oracle keeps numbers in following way: 1 byte for power, 1 byte for the first significand digit (that is one before the separator), the rest for the other digits.

By digits here Oracle means centennial digits (i. e. base 100)

SQL> INSERT INTO t_numtest VALUES (LPAD('9', 125, '9'))
  2  /

1 row inserted

SQL> INSERT INTO t_numtest VALUES (LPAD('7', 125, '7'))
  2  /

1 row inserted

SQL> INSERT INTO t_numtest VALUES (LPAD('9', 126, '9'))
  2  /

INSERT INTO t_numtest VALUES (LPAD('9', 126, '9'))

ORA-01426: numeric overflow

SQL> SELECT DUMP(num) FROM t_numtest;

DUMP(NUM)
--------------------------------------------------------------------------------
Typ=2 Len=2: 255,11
Typ=2 Len=21: 255,8,78,78,78,78,78,78,78,78,78,78,78,78,78,78,78,78,78,78,79

As we can see, the maximal number here is 7.(7) * 10^124, and he have 19 centennial digits for precision, or 38 decimal digits.